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Application of hydraulic, components of hydraulic system, troubleshooting of hydraulic system.
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- 1. Hydraulic System Presented By; Bhavesh Solanki
- 2. Content • Introduction • Hydraulic System • Components of Hydraulic System ▪ Reservoir ▪ Filters ▪ Control Valves ▪ Hydraulic Pump ▪ Accumulators ▪ Actuators • Hydraulic Truck Unloader • Hydraulic Chain Drive • Troubleshooting
- 3. Power Transmission • Power transmission is the movement of energy from its place of generation to a location where it is applied to perform useful work. • In the industry we use three methods for transmitting power from one point to another. • Mechanical transmission is through shafts, gears, couplings, chains, belts, etc. • Electrical transmission is through wires, transformers, rectifiers, etc. • Fluid power is through liquids or gas in a confined space.
- 4. Fluid Power • Fluid power is the method of using pressurized fluid to transmit energy. • Liquid or Gas is referred to as a fluid. • Accordingly, there are two branches of fluid power; Pneumatics, and Hydraulics. • Hydraulic systems use pressurized liquid such as water or other liquids to transfer Power from one point to another. • Pneumatic systems use pressurized air or other gases to transfer Power from one point to another.
- 5. Hydraulic • Two Greek word, hudro (Water) + aulos (Pipe) → hudraulikos • hudraulikos (Greek) → hydraulic (Latin) early 17th century • Hydraulics is the science of forces and movements transmitted by means of liquids. • Pressurized liquid act as a medium of power transmission. • Hydraulic fluids are incompressible. These fluids doesn’t change to smaller size when squeezing forces are applied.
- 6. Application of Hydraulic • Hydraulic systems are commonly used where mechanisms require large forces and precise control. • Hydraulics plays an important role in many industries; there are a lot of hydraulic applications in manufacturing, transportation, and construction sectors. • Examples include vehicle power steering and brakes, hydraulic jacks, hydraulic elevators, Weapons systems (loading & launching), and heavy earth moving machines. • Heavy duty presses for bulk metal formation such as sheet metal bending, forging, punching etc.
- 7. Hydrostatics • A hydrostatic system uses fluid pressure to transmit power. • The system creates high pressure, and through a transmission line and a control element, this pressure drives an actuator (linear or rotational). • Hydrostatic transmission: Small Flow rate & Large Pressure Head • The pump used in hydrostatic systems is a positive displacement pump. • An example of pure hydrostatics is the transfer of force in hydraulics. • Linear movement against large force, Linear movement and stopping in exact position : hydrostatics
- 8. Pressure • Pressure is the magnitude F of a force acting perpendicular to a surface divided by the area S of the surface over which the force acts. P = 𝐹 𝐴 (SI unit Τ𝑁 𝑚2 or Pascal) 0 10 20 30 40 50 60 0 2 4 6 Force(N) Area (m^2) 0 100 200 300 400 500 600 0 20 40 60 Pressure Area For Given Pressure Force 𝜶 Area For Given Force Pressure 𝜶 1/Area 0 5 10 15 20 25 30 0 20 40 60 Pressure(Pa) Force (N) For Given Area Pressure 𝜶 Force
- 9. Hydrostatic Pressure • The pressure at a point in a liquid in static equilibrium depends only on the depth at that point 𝑷 = 𝑷 𝟎 + 𝝆·g·H • Where 𝑷 𝟎 is the external pressure on the surface of the liquid, H is the depth, g is the gravity acceleration and 𝝆 is the liquid density • Hydrostatic pressure inside the water in a dam or a swimming pool increases with depth • That is the reason of the trapezoidal shape of walls in dams and swimming pools
- 10. Pascal’s Principle • Any change in the pressure applied to a completely enclosed fluid is transmitted equally in all directions and walls of enclose without any loss. • French scientist pascal discovered this law in the 17th century. • When the syringe is filled with water, pushing the plunger water comes out from all nozzles with equal speed perpendicularly to the surface of the container
- 11. Pascal’s Law • P = 𝐹1 𝐴1 • 𝐹2 = P x 𝐴2 • Magnitude of force transferred is in direct proportion to the surface area (F = P*A) 𝐹1 𝐹2 Small Area 𝐴1 Large Area 𝐴2 Pressure P
- 12. Pascal’s Law application
- 13. Law of Conservation of Energy • Energy can neither be created nor destroyed. what is gained by force is sacrificed in the distance moved.
- 14. Archimedes’ Principle • Buoyancy: Buoyancy is an upward force exerted by a fluid that opposes the weight of a partially or completely immersed object. • Archimedes' principle states that the upward buoyant force that is exerted on a body immersed in a fluid, whether fully or partially submerged, is equal to the weight of the fluid that the body displaces and acts in the upward direction at the center of mass of the displaced fluid • Buoyant force = Fluid Density x g x Volume of displaced fluid 𝑭𝑩 = 𝒅𝒇 ∙ 𝒈 ∙ 𝑽𝒇 • If object density < Fluid density → object will Float • If object density > Fluid density → object will Sinks
- 15. Hydrodynamic • Hydrodynamic systems use fluid motion to transmit power. Power is transmitted by the kinetic energy of the fluid. Hydrodynamics deals with the mechanics of moving fluid and uses flow theory. • Hydrodynamic transmission: Large Flow rate & Small Pressure Head • An example of pure hydrodynamics is the conversion of flow energy in turbines in hydroelectric power plants. The pump used in hydrodynamic systems is a non-positive displacement pump.
- 16. Continuity Equation: • Mass enter in tube = Mass exit from tube (for given time) • ∆𝑚1 = ∆𝑚2 • 𝜌 ∆𝑉1 = 𝜌 ∆𝑉2 • 𝐴1 ∆𝑋1 = 𝐴2 ∆𝑋2 (Incompressible Fluid) 𝐴1 𝑣1 = 𝐴2 𝑣2 • 𝐴1 𝑣1∆𝑡 = 𝐴2 𝑣2 ∆𝑡 Bernoulli’s Equation ∆𝑈 = Q + W (Thermodynamics' First Law or Energy Conservation) 1 2 𝑀𝑣1 2 - 1 2 𝑀𝑣2 2 +𝑀 𝑔 𝑦1 - 𝑀 𝑔 𝑦2 = (𝑃2 −𝑃1)∆𝑉 (𝑚1 = 𝑚2 = M) 1 2 𝜌 ∆𝑉 𝑣1 2 - 1 2 𝜌 ∆𝑉 𝑣2 2 + 𝜌 ∆𝑉 𝑔 𝑦1 - 𝜌 ∆𝑉 𝑔 𝑦2 = (𝑃2 −𝑃1)∆𝑉 𝑃1 + 1 2 𝜌 𝑣1 2 + 𝜌 𝑔 𝑦1 = 𝑃2 + 1 2 𝜌 𝑣2 2 + 𝜌 𝑔 𝑦2 𝑃1 𝜌 𝑔 + 𝑣1 2 2𝑔 + 𝑦1 = 𝑃2 𝜌 𝑔 + 𝑣2 2 2𝑔 + 𝑦2
- 17. Hydraulic System • Hydraulic circuits composed of pumps, pressure control valve, direction control valve, flow control valve, actuators, Reservoir and accessories, and their composition according to objectives and specifications. Many compositions are possible for single objective. • The most efficient circuit is, 1) Safe and completely optimal to meet objective. 2) Capable of smooth movement. 3) Energy efficient. 4) Effective for initial and running costs. 5) Easy to maintain.
- 18. Schematic of Hydraulic System
- 19. Structure of hydraulic system Power Supply Section • Prime Mover (Motor, Engine) • Coupling • Pump • Reservoir • Filter Power Control Section • Direction control Valve • Flow Control Valve • Pressure Control Valve • Non Return Valve Drive Section • Linear Actuator (Cylinders) • Rotary Actuator (Motors) Hydraulic Power Section Signal Input (Sensing) • Manually • Mechanically • Contactlessly Signal Processing • By the operator • By Electrically • By Pneumatics • By Hydraulics • By Mechanics Signal Control Section
- 20. Power Transmission Hydraulic Cylinder Electric Motor T x ω V x I Hydraulic Pump P x Q Hydraulic Motor F x v T x ω Hydraulic System Electrical Energy Mechanical Energy Hydraulic Energy Mechanical Energy
- 21. Input and Output power
- 22. Components of Hydraulic System 1. Reservoir 2. Filters 3. Control Valves 4. Pumps 5. Accumulators 6. Actuators
- 23. 1. Hydraulic Reservoir
- 24. • Reservoir is supply source of hydraulic system fluid. • A well designed and constructed reservoir assists the separation of contamination and helps to dissipate heat generate with in the system. • The large removable covers on each end permits easy access for cleaning. One of the cover has fluid level indicator to check fluid level periodically. • Most tanks are of welded construction with supports for mounting for easy access to the drain plug. • A tank must be totally enclosed and should have a filtered air breather to screen out particles from the surrounding air. • Contaminant are screened out using a strainer and a filter. Some reservoirs have magnetic plugs to trap iron and steel particles carried by the fluid.
- 25. Baffle Plate • A Baffle plate extending length wise through the tank separates the pump inlet line from the system return, preventing continuous recirculation of the same fluid. • Thus any foreign particles in the fluid are allowed to settle to the bottom and trapped air is permitted to escape. It also helps maintain an even fluid temperature.
- 26. Air Breather • In every closed hydraulic tanks air breather mounted on air chamber side and its function to maintain the pressure on hydraulic oil. • When breath in it allows air to exit and enter the reservoir as the fluid level rises and falls, respectively but prevents the entry of particles, such as dust, wet air. • When breath-out (suddenly) oil mists get sprayed/spilled out. To filter the dust and suppress the oil mist, fine filter (wire mesh) elements are used. • Oil mist and dust together forms a pasty mass and could block the breathing. Regular cleaning of filter and replacements of drying elements are necessary. 2. Hydraulic Filters
- 27. Suction Strainer • A strainer is the primary filtering system that removes large particles of foreign matter from a hydraulic liquid. Even though its screening action is not as good as a filter’s, a strainer offer less resistance to flow. • A Strainer is a device for the removal of solids from a fluid wherein the resistance to motion of such solid in straight line. • A strainer usually consists of a metal frame wrapped with a fine-mesh wire screen or a screening element made up of varying thickness of specially processed wire. • Strainers are used to pump inlet lines where pressure drop must be kept to a minimum and also protect the pump from large, damaging contamination particles that can cause failure.
- 28. • A suction strainer or filter should have a bypass relief valve. when the strainer becomes clogged. The reasoning behind this is that the pump will run many hours on contaminated oil, but will fail in a few minutes with little or no oil.
- 29. Pressure line Filter • Located downstream from the hydraulic pump, these filters are designed to clean the fluid as it exits the pump to protect more sensitive system components such as control valves and actuators from contaminants generated from the pump. • The typical filtering media used in these filters is capable of removing a high percentage of the smaller particles of contaminant. When there is a high pressure drop across the filter, the element must not collapse. • A pressure-line filter should not have a bypass. If the filter element clogs, it is better to stop flow to servo valves than to contaminate them. • Indicators on the filters warn of clogging to allow the elements to be changed before production speed is affected.
- 30. Return line filter • Located between the control valve and the fluid reservoir, these filters are designed to capture wear debris from the hydraulic systems working components before returning the fluid back to the reservoir. • The media used in these filters is designed to remove common size wear particles that may be generated by these system components. • Return-line filters should have integral bypass check valves. If the filter becomes loaded, return oil needs a flow path to tank until it is convenient to change the filter. • Without a bypass, the filter element may collapse, or the element housing or seal may rupture.
- 31. Off line filtration • These filters are used, independent from the hydraulic system. Fluid is pulled from the reservoir through the filter and is returned to the reservoir. • Sometimes called kidney filters or bypass filters. • When the off-line filter indicator shows a clogged element, the main hydraulic circuit can continue to run during filter change. • Also, this type filter system can operate while the main hydraulic circuit is shut off over nights or weekends.
- 32. Pressure relief valve • Pressure-relief valves limit the maximum pressure in a hydraulic circuit by providing an alternate path for fluid flow when the pressure reaches a preset level. • All fixed-volume pump circuits require a relief valve to protect the system from excess pressure. • It is normally a closed valve whose function is to limit the pressure to a specified maximum value by diverting pump flow back to the tank. • Note the external adjusting screw, which varies spring force and, thus, the pressure at which the valve begins to open (cracking pressure). 3. Control Valves
- 33. Flow control Valve Non-Pressure-Compensated Valves • Non-pressure-compensated flow-control valves are used when the system pressure is relatively constant and motoring speeds are not too critical. • The operating principle behind these valves is that the flow through an orifice remains constant if the pressure drop across it remains the same. In other words, the rate of flow through an orifice depends on the pressure drop across it. • The inlet pressure is the pressure from the pump that remains constant. Therefore, the variation in pressure occurs at the outlet that is defined by the work load. • This implies that the flow rate depends on the work load. Hence, the speed of the piston cannot be defined accurately using non-pressure-compensated flow-control valves when the working load varies.
- 34. • Pressure-Compensated Valves • It overcome the difficulty caused by non-pressure-compensated valves by changing the size of the orifice in relation to the changes in the system pressure. • Once the valve is set, the pressure compensator acts to keep the pressure drop nearly constant. • It works on a kind of feedback mechanism from the outlet pressure. This keeps the flow through the orifice nearly constant
- 35. Speed Control of a Hydraulic Cylinder using a flow control valve (Meter–In) • It control the fluid flow just before fluid enters to the actuator with the help of flow control valve. we can also say that there could be a restriction in fluid flow to the actuator. • Meter-in flow control circuit will have quite precise control if load is resistive load but if there will be overrunning load then in that situation meter-in circuit will not be able to control the actuator speed. • In case of overrunning load, actuator will move faster and hydraulic circuit will not be able to fill it with hydraulic fluid and hence cavitation phenomena will be possible over there.
- 36. Speed Control of a Hydraulic Cylinder using a flow control valve (Meter–Out) • Flow control valve will be installed on discharge end or return side of actuator i.e. cylinder in order to control the discharge of fluid flow. Meter-out flow control circuit will control the flow of fluid leaving the actuator. • Actuator speed will be controlled in meter-out circuit by restricting the flow of fluid leaving the actuator. • Meter-out circuit will work successfully with resistive load and also with overrunning load or running away load because actuator will not be able to move faster than fluid discharge it permits.
- 37. Counter Balance valve
- 38. Internally & Externally Piloted Counter Balance valve
- 39. Direction control valve • A valve is a device that receives an external signal (mechanical, fluid pilot signal, electrical or electronics) to release, stop or redirect the fluid that flows through it. • The function of a DCV is to control the direction of fluid flow in any hydraulic system. A DCV does this by changing the position of internal movable parts. A B P T A B P T
- 40. Check Valve o The simplest type of direction control valve is a check valve o it is a two-way valve because it contains two ports. o The purpose of a check valve is to permit free flow in one direction and prevent any flow in the opposite direction (a) (b) Figure5-1 Inline check valve (a) Construction.(b) Graphic symbol inletP1 outletP2 valve seat ball bias spring body inletP1 outletP2 Poppet check valve: (a) Open and (b) closed position
- 41. Shuttle Valve • A shuttle valve allows two alternate flow sources to be connected to one branch circuit.
- 42. Sliding Spool Valves Most directional control valves use a sliding spool to change the path of flow through the valve. • Position ：For a given position of the spool, a unique flow path configuration exists within the valve. • Way: The number of “ways” refers to the number of ports in the valve. • Normal/Neutral/center position: The spool is not actuated A BP T A P TB
- 43. • Two way, Two position, normally closed direction control valve. • Ex. A pair of two-way valves is used to fill and drain a vessel. • Three way, Two position, normally closed direction control valve. • Ex. Single acting cylinder, Double acting with pair of normally closed & normally open. • Four way, Two position, normally closed direction control valve. • Ex. Bi directional Hydraulic Motor, Double Acting Cylinder
- 44. TP BA A P TB A BA TP B TP A TP B P T P T A B A B 4-way, 3-position directional control valves
- 45. A B TP AT(T1) P T(T2)B TP A B AT(T1) P T(T2)B TP BA AT(T1) P T(T2)B Figure 5-12 Various center flow paths for three-position,four-way valve open center pressure andB closed;A open to tank closed center--all ports closed tandem B closed; pressure open to tank throughA pressure closed;A & B open to tank T(T1) ATP BA P T T(T1) A A B P T T(T1) A A B B T(T2)P T(T2)BP T(T2)BP Center positions in three-position, four-way valves
- 46. Actuating Devices • Manually operated: In manually operated DCVs, the spool is shifted manually by moving a handle pushing a button or stepping on a foot pedal. When the handle is not operated, the spool returns to its original position by means of a spring. • Mechanically operated: The spool is shifted by mechanical linkages such as cam and rollers. • Solenoid operated: When an electric coil or a solenoid is energized, it creates a magnetic force that pulls the armature into the coil. This causes the armature to push the spool of the valve. • Pilot operated: A DCV can also be shifted by applying a pilot signal (either hydraulic or pneumatic) against a piston at either end of the valve spool. When pilot pressure is introduced, it pushes the piston to shift the spool.
- 47. A B T B P Aspring body spool hand lever Figure 5-13 Manually actuated, spring-centered, three-position, four-way valve (a) Construction (b) Complete graphic symbol (a) (b) TP v a (a) (b) P A 5-14 Mechanically-actuated two-way valve (a) Construction (b) Complete graphic symbol AProllercam body spring Figure Mechanically-actuated valveManually-actuated valve A B K1 K2 T P T (a) (b) TP BA K1 K2 Figure 5-15 Oil pilot-actuated four-way valve (a) Construction (b) Complete graphic symbol body spoolspring Pilot-actuated valve T P A B Figure 5-17 Solenoid-actuated directional control valve. solenoid spool spring armaturecoil Solenoid-actuated valve
- 48. Solenoid Controlled Pilot operated DCV
- 49. 4. Hydraulic Pump • Hydraulic Pump take oil from reservoir and supply to the hydraulic system. • Pump Produces fluid motion or flow it does not generate pressure. But, the resistance to output fluid flow generates the pressure. • It means that if the discharge port (output) of a pump is opened to the atmosphere, then fluid flow will not generate any output pressure above atmospheric pressure. • But, if the discharge port is partially blocked, then the pressure will rise due to the increase in fluid flow resistance. • Hydraulic Pumps are classified in two categories: (1) Non Positive Displacement pump (2) Positive displacement pump.
- 50. • Fluid motion or flow created by rotation of impeller. These pumps generally used for low-pressure and high-volume flow applications. • It provide continuous flow but output decrease with increase in system resistance(Load). • If the output port of a non-positive-displacement pump were blocked off, the pressure would rise, and output would decrease to zero. Although the pumping element would continue moving, flow would stop because of slippage inside the pump. • Advantages of these pumps are lower initial cost, less operating maintenance because of less moving parts, simplicity of operation, higher reliability and suitability with wide range of fluid etc. • These pumps are primarily used for transporting fluids and find little use in the hydraulic or fluid power industry. Non-Positive Displacement Pumps (Hydro-dynamic)
- 51. Positive Displacement Pumps • For each pump revolution ▪ Fixed amount of liquid taken from one end & Positively discharged at other end ▪ A specific amount of fluid passes through the pump for each rotation ▪ The output fluid flow is constant and is independent of the system pressure (load). • Fluid flow is proportional to their displacement and rotor speed. • The input and output region are separated and hence the fluid cannot leak back due to higher pressure at the outlets. Because of this reason these pumps are mostly used in hydraulic system. • If pipe blocked ▪ Pressure rises It can damage the pump ▪ In order to avoid this happening, Relief valve is required • They are highly efficient and almost constant throughout the designed pressure range. They are a compact unit having a high power to weight ratio
- 52. Classification of Pump Pump Positive Displacement Rotary Gear Pump Lobe Pump Screw Pump Vane Pump Cam Pump Reciprocating Piston Pump Plunger Pump Diaphragm Pump Roto dynamic Centrifugal Pump Axial Pump
- 53. Reciprocating Positive Displacement Pump • Reciprocating pumps move the fluid using one or more oscillating pistons, plunger, or membranes (diaphragm), while valves restrict fluid motion to the desired direction. • They provide high efficiency, high pressure, low noise level, high reliability with low speed. • Reciprocating pump use in high pressure application like hydraulic system of jet air crafts, Presses, plastic injection molding, automotive sector (automatic transmission, hydraulic suspension control). • Piston pump can handle hydraulic fluid or Oil. Diaphragm pump can handle very corrosive, abrasive, volatile, viscous slurries with crystal or particles.
- 54. Piston Pump Axial Piston Pump Triplex Plunger Pump Radial Piston Pump Diaphragm Pump
- 55. Rotary Positive Displacement Pump • The working of all the rotary type positive displacement pumps are based on the same principle, i.e pumping of the liquid with the help of rotating elements. The rotating elements can be gears, screws, vanes or cam, etc. • The discharge of rotary pumps is smooth, continuous and not pulsating. A very less vibration and noise is observed. They are compact with less number of moving component and less sensitive to contaminations. • Close tolerances between the moving & stationary parts minimize leakage from the discharge space back to the suction space. • Rotary pumps operate best on clean, moderately viscous fluids such as light lubricating oil.
- 56. 5. Hydraulic accumulators • A Hydraulic Accumulator is energy storage device. • A hydraulic accumulator is a device in which the potential energy of an incompressible fluid is held under pressure by an external source against some dynamic force from sources like gravity, mechanical spring and compressed gas. • The potential energy is stored when the demand of energy by the system is less than that available from the prime mover and is released to the system during its period of peak demand of energy which the prime mover alone cannot meet. • Its function is analogous to that of the flywheel in a mechanical system.
- 57. Types of Hydraulic Accumulators 1. Weight-loaded or gravity accumulator • The weight applies a force on the piston that generates a pressure on the fluid side of piston. • The advantage of this type of accumulator over other types is that it applies a constant pressure on the fluid throughout its range of motion. • The main disadvantage is its extremely large size and heavy weight. This makes it unsuitable for mobile application.
- 58. 2. Spring Loaded Accumulators • The spring is a source of energy acting against the piston. The pressure created by this type of accumulator depends upon the stiffness and pre- loading of spring. • The pressure exerted on the fluid is not constant. As the springs are compressed, the accumulator pressure reaches its peak. • It typically delivers a low flow rate of oil at low pressures, so for high pressure situations, these type of accumulator are somewhat heavy. • This are not suitable for application demanding high cycle rates as the spring may fail in fatigue and lose its elasticity.
- 59. 3. Gas Charged Accumulators • These are also known as hydro-pneumatic accumulators because in this type the force is applied to the oil using compressed air. • The storage of potential energy is due to the compressibility nature of the gas. • The expansion of the gas forces the oil out of the accumulator. • Here the oil and gas are separated by an element or a diaphragm. Depending on type of element used to separate the oil and gas, they classified as a ✓Piston type accumulators ✓Diaphragm type accumulators ✓Bladder or Bag type accumulators • Only nitrogen gas is used to charge a gas filled with accumulator. Nitrogen is chemically inert, non-flammable and does not combine easily with other elements.
- 60. Piston Type Accumulator Bladder Type Accumulator Diaphragm Type Accumulator
- 61. 6. Hydraulic Actuators • Hydraulic actuators convert hydraulic energy into mechanical energy. • The amount of output power developed depends upon the flow rate, pressure drop across the actuator and its overall efficiency. • Thus they are devices which used to convert pressure energy of the fluid In to mechanical energy. • Depending on the type of actuation, hydraulic actuators are classified as, 1) Linear Actuators: for linear actuation (hydraulic cylinder) 2) Rotary Actuators: for rotary actuation(hydraulic motor)
- 62. Linear actuator (hydraulic cylinder) • Provides motion in straight line. • Linear displacement depends on stroke length. • Usually referred to as cylinders, rams (single acting cylinders) or jacks.
- 63. Rotary actuators (Hydraulic motors) • Produces continuous rotational motion. • Pump shaft is rotated to generate flow. • A motor shaft is caused to rotate by fluid being forced into the driving chambers.
- 64. Troubleshooting Problem Possible Causes Remedies Excessive Noise Coupling Misalignment Align unit and check condition of seals, bearings and coupling. Cavitation Clean or replace dirty Filters, Air Breather, Clean Clogged inlet line, Change System Fluid, Change to proper Pump drive Motor Speed. Worn Poppet & Seat of Relief Valve Replace Relief Valve Air Entrainment Tighten leaking connections; fill reservoir to proper level; bleed air from system; replace pump shaft seal (and shaft if worn or damaged).
- 65. Problem Possible Causes Remedies Excessive Heat System Pressure To High Install pressure gauge and adjust to correct pressure (If Relief Valve & Unloading Valve Set To High). Cavitation & Air Entrainment Excessive Load Check for work load in excess of circuit design, Align unit and check condition of seals and bearings; Fluid Dirty or Low Supply Change filters and also system fluid if improper viscosity; fill reservoir to proper level. Faulty fluid cooling system Clean cooler and/or cooler strainer; replace cooler control valve; repair or replace cooler.
- 66. Problem Possible Causes Remedies Incorrect Flow Pump Not Receiving Fluid Replace/Clean Inlet Filter, inlet clogged line, air Breather; Maintain Proper Oil level in reservoir. Flow passing over relief valve Adjust at High Motor Turning in Wrong Direction Reverse Direction RPM of Pump drive Motor Incorrect Replace With Correct Unit Drive to Pump Coupling Sheared Align and replace Coupling External Leak In System Tighten leaking Connection Direction Control Set In Wrong Position Check position of manually operated Controls, Check Electrical Circuit On Solenoid Operated Controls. Damaged Pump Replace or Overhaul Pump
- 67. Problem Possible Causes Remedies Incorrect Pressure No Flow Replace Dirty Filter & Clogged Lines, Replace dirty Fluid. Air In Fluid Tighten leaking connections; fill reservoir to proper level; bleed air from system; replace pump shaft seal (and shaft if worn or damaged). Relief Valve Set High or Low Adjust Counter Balance Valve Misadjusted Damaged Pump or Cylinder Replace or Overhaul Accumulators defective or has lost charge Replace or Charge
- 68. Problem Possible Causes Remedies Faulty Operation No Movement No Flow, No Pressure No Command Signal or Wrong Signal Check Electrical Connection Inoperative Servo Valve Adjust, Repair or Replace Low Movement Relief Valve set too Low Adjust External Leak In System Tighten leaking Connection Low RPM of drive Replace with Correct Unit Worn or Damaged Cylinder & Pump Replace or Overhaul Erratic Movement Sticking of Servo Valve Clean or Repair, Check Fluid & Filter Condition Erratic Command Signal Repair Command Console or Connections Malfunctioning feedback transducer Repair or Replace Excessive Movement Improper Size of Pump Replace With Correct Unit High RPM of drive Worn or Damaged Flow Control Valve or Counter Balance Valve Repair or Replace
- 69. Thank You
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Introduction to hydraulics
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Hydraulics. Hydraulics. hy·drau·lics study of fluids: the study of water or other fluids at rest or in motion, especially with respect to engineering applications. Objectives. Behavior of liquids & theory of operation Basic hydraulic system components
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Hydraulics • hy·drau·licsstudy of fluids: the study of water or other fluids at rest or in motion, especially with respect to engineering applications
Objectives • Behavior of liquids & theory of operation • Basic hydraulic system components • Advantages & disadvantages of hydraulics • Project
Introduction/Uses • Hydraulics used in many applications: • Steering/control systems (rudder, planes) • Deck machinery (anchor windlass, capstans, winches) • Masts & antennae on submarines • Weapons systems (loading & launching) • Other: elevators, presses
Hydraulic Theory • Hydraulics • Covers the physical behavior of liquids in motion • Pressurized oil used to gain mechanical advantage and perform work • Important Properties • Shapelessness • Incompressibility • Transmission of Force
Important Properties • “Shapelessness” • Liquids have no neutral form • Conform to shape of container • Easily transferred through piping from one location to another • Incompressibility • Liquids are essentially incompressible • Once force is removed, liquid returns to original volume (no permanent distortion) • Transmission of Force • Force is transmitted equally & undiminished in every direction -> vessel filled with pressure
Hydraulic Theory • Pascal’s Law • Magnitude of force transferred is in direct proportion to the surface area (F = P*A) • Pressure = Force/Area • Liquid properties enable large objects (rudder, planes, etc) to be moved smoothly
Hydraulic Mechanical Advantage
Basic Hydraulic System • Hydraulic Fluid • Usually oil (2190 TEP) • Pressure Source • Hydraulic pump (A-end of system) • Pressure user • Hydraulic motor (B-end of system) • Piping system (w/ valves, tanks, etc) • Get fluid from A-end to B-end
Hydraulic Pump (A-End) • Pumps can be positive displacement or centrifugal • Waterbury pump • Variable-stroke piston pump • Tilting box can tilt fwd/aft while pump rotates • Angle of tilting box determines capacity and direction of oil flow
Hydraulic Pump (A-End) • Variable-stroke piston pump • Tilting box can tilt fwd/aft while pump rotates • Angle of tilting box determines capacity and dir. of flow
Cylinder/Motor (B-end) • Piston/cylinder used if desired motion is linear • Hydraulic pressure moves piston & ram • Load is connected to ram (rudder, planes, masts, periscopes) Cylinder Piston RAM Seal Hydraulic Fluid Supply/Return Ports
Cylinder/Motor (B-end) • Motor used if desired motion is rotary • Essentially a variable-stroke pump in reverse • Used for capstan, anchor windlass, etc
Piping System • Has to withstand excessive pressure • Valves, filters, & HX’s all necessary • Accumulators • Holds system under pressure (w/out contin. pump) • Provides hydraulics when pump off/lost • Compensates for leakage/makeup volume • Types: piston, bladder, & direct contact
Accumulator Types • Piston • Most common • Bladder • Gun mounts • Steering systems • Direct contact • Least common
Advantages • Convenient power transfer • Few moving parts • Low losses over long distances • Little wear • Flexibility • Distribute force in multiple directions • Safe and reliable for many uses • Can be stored under pressure for long periods • Variable speed control • Quick response (linear and rotary)
Disadvantages • Requires positive confinement (to give shape) • Fire/explosive hazard if leaks or ruptures • Filtration critical - must be free of debris • Manpower intensive to clean up
Hydraulics Hydraulics Video Hydraulic Circuit
Project • Research different applications of a hydraulic system. • Take that system image place it in word. Write a description on how the system flows and functions. • Find dimension for that system and recreate it in pro-engineering. • You’ll need part, files assembly files, rending, and animation of the system working.
basics of hydraulics - PowerPoint PPT Presentation
basics of hydraulics
Full basics – powerpoint ppt presentation.
- Explain fundamental hydraulic principles.
- Apply the laws of hydraulics.
- Calculate force, pressure, and area.
- Describe the function of pumps, valves, actuators, and motors.
- Describe the construction of hydraulic conductors and couplers.
- The term hydraulics is used to specifically describe fluid power circuits that use liquidsespecially formulated oilsin confined circuits to transmit force or motion.
- Hydraulic circuits
- Hydraulic brakes
- Power steering systems
- Automatic transmissions
- Fuel systems
- Wet-line kits for dump trucks
- Torque converters
- Pressure applied to a confined liquid is transmitted undiminished in all directions and acts with equal force on all equal areas, at right angles to those areas.
- Hydrostatics is the science of transmitting force by pushing on a confined liquid.
- In a hydrostatic system, transfer of energy takes place because a confined liquid is subject to pressure.
- Hydrodynamics is the science of moving liquids to transmit energy.
- We can define hydrostatics and hydrodynamics as follows
- Hydrostatics low fluid movement with high system pressures
- Hydrodynamics high fluid velocity with lower system pressures
- A column of air measuring 1 square inch extending 50 miles into the sky would weigh 14.7 pounds at sea level.
- If we stood on a high mountain, the column of air would measure less than 50 miles and the result would be a lower weight of air in the column.
- Similarly, if we were below sea level, in a mine for instance, the weight of air would be greater in the column.
- In North America, we sometimes use the term atm (short for atmosphere) to describe a unit of measurement of atmospheric pressure.
- Europeans use the unit bar (short for barometric pressure).
- Force is push or pull effort.
- The weight of one object placed upon another exerts force on it proportional to its weight.
- If the objects were glued to each other and we lifted the upper one, a pull force would be exerted by the lower object proportional to its weight.
- Force does not always result in any work done.
- If you were to push on the rear of a parked transport truck, you could apply a lot of force, but that effort would be unlikely to result in any movement of the truck.
- The formula for force (F) is calculated by multiplying pressure (P) by the area (A) it acts on.
- There are a number of different pressure scales used today but all are based on atmospheric pressure. One unit of atmosphere is the equivalent of atmospheric pressure and it can be expressed in all these ways
- 1 atm 1 bar (European)
- 29.920 Hg (inches of mercury)
- 101.3 kPa (metric)
- However, each of the above values is not precisely equivalent to the others
- 1atm 1.0192 bar
- 1 bar 29.530 Hg 14.503 psia
- 10 Hg 13.60 H2O _at_ 60 F
- Evangelista Torricelli (16081647) discovered the concept of atmospheric pressure.
- He inverted a tube filled with mercury into a bowl of the liquid and then observed that the column of mercury in the tube fell until atmospheric pressure acting on the surface balanced against the vacuum created in the tube.
- At sea level, vacuum in the column in Torricellis tube would support 29.92 inches of mercury.
- A manometer is a single tube arranged in a U-shape used to measure very small pressure values.
- It may be filled to the zero on the calibration scale with either water H2O) or mercury (Hg), depending on the pressure range desired.
- A manometer can measure either push or pull on the fluid column. Examples
- Crankcase pressure
- Exhaust backpressure
- Air inlet restriction
- Absolute pressure uses a scale in which the zero point is a complete absence of pressure.
- Gauge pressure has as its zero point atmospheric pressure.
- A gauge therefore reads zero when exposed to the atmosphere.
- To avoid confusing absolute pressure with gauge pressure
- Absolute pressure is expressed as psia.
- Gauge pressure is usually expressed as psi or psig.
- Hydraulic levers can be used to demonstrate Pascals law
- Pressure equals force divided by the sectional area on which it acts.
- Force equals pressure multiplied by area.
- One of the cylinders has a sectional area of 1sq. and the other 50 sq.
- Applying a force of 2 lbs. on the piston in the smaller cylinder would lift a weight of 100 lbs.
- Applying a force of 2 lbs. on the piston in the smaller cylinder produces a circuit pressure of 2 psi.
- The circuit potential is 2 psi and because this acts on a sectional area of 50 sq., it can raise 100 lbs.
- If a force of 10 lbs. was to be applied to the smaller piston, the resulting circuit pressure would be 10 psi and the circuit would have the potential to raise a weight of 500 lbs.
- Flow is the term we use to describe the movement of a hydraulic fluid through a circuit.
- Flow occurs when there is a difference in pressure between two points.
- In a hydraulic circuit, flow is created by a device such as a pump.
- A pump exerts push effort on a fluid.
- Flow rate is the volume or mass of fluid passing through a conductor over a given unit of time.
- An example would be gallons per minute (gpm).
- Given an equal flow rate, a small cylinder will move faster than a larger cylinder. If the objective is to increase the speed at which a load moves, then
- Decrease the size (sectional area) of the cylinder.
- Increase the flow to the cylinder (gpm).
- The opposite would also be true, so if the objective were to slow the speed at which a load moves, then
- Increase the size (sectional area) of the cylinder.
- Decrease the flow to the cylinder (gpm).
- Therefore, the speed of a cylinder is proportional to the flow to which it is subject and inversely proportional to the piston area.
- In a confined hydraulic circuit, whenever there is flow, a pressure drop results.
- Again, the opposite applies. Whenever there is a difference in pressure, there must be flow.
- Should the pressure difference be too great to establish equilibrium, there would be continuous flow.
- In a flowing hydraulic circuit, pressure is always highest upstream and lowest downstream. This is why we use the term pressure drop.
- A pressure drop always occurs downstream from a restriction in a circuit.
- Pressure drop will occur whenever there is a restriction to flow.
- A restriction in a circuit may be unintended (such as a collapsed line) or intended (such as a restrictive orifice).
- The smaller the line or passage through which the hydraulic fluid is forced, the greater the pressure drop.
- The energy lost due to a pressure drop is converted to heat energy.
- Work occurs when effort or force produces an observable result.
- In a hydraulic circuit, this means moving a load.
- To produce work in a hydraulic circuit, there must be flow.
- Work is measured in units of force multiplied by distance, for example, in pound-feet.
- Work Force x Distance
- Bernoullis Principle states that if flow in a circuit is constant, then the sum of the pressure and kinetic energy must also be constant.
- Pressure x Velocity IN Pressure x Velocity OUT
- When fluid is forced through areas of different diameters, fluid velocity changes accordingly.
- For example, fluid flow through a large pipe will be slow until the large pipe reduces to a smaller pipe then the fluid velocity will increase.
- Flow of a hydraulic medium through a circuit should be as streamlined as possible.
- Streamlined flow is known as laminar flow.
- Laminar flow is required to minimize friction.
- Changes in section, sharp turns, and high flow speeds can cause turbulence and cross-currents in a hydraulic circuit, resulting in friction losses and pressure drops.
- Hydraulic systems can be grouped into two main categories
- Open-center systems
- Closed-center systems
- The primary difference between open-center and closed-center systems has to do with what happens to the hydraulic oil in the circuit after it leaves the pump.
- In an open-center system, the pump runs constantly and oil circulates within the system continuously.
- An open-center valve manages flow through the circuit. When this valve is in its neutral position, fluid returns to the reservoir.
- An example of an open-center hydraulic system on a truck is power-assisted steering.
- In a closed-center system, the pump can be rested during operation whenever flow is not required to operate an actuator.
- The control valve blocks flow from the pump when it is in its closed or neutral position.
- A closed-center system requires the use of either a variable displacement pump or proportioning control valves.
- Closed-center systems have many uses on agricultural and industrial equipment, but on trucks, they would be used on garbage packers and front bucket forks.
- In hydraulics, force is the product of pressure multiplied by area.
- Force Pressure x Area
- For instance, if a fluid pressure of 100 psi acts on a piston sectional area of 50 square inches it means that 100 pounds of pressure acts on each square inch of the total sectional area of the piston. The linear force in this example can be calculated as follows
- Force 100 psi x 50 sq. in. 5000 lbs.
- Hydraulic motors
- Conductors and connectors
- Hydraulic fluids
- A reservoir in a hydraulic system has the following roles
- Stores hydraulic oil
- Helps keep oil clean and free of air
- Acts as a heat exchanger to help cool the oil
- A reservoir is typically equipped with
- Oil-level gauge or dipstick
- Outlet and return lines
- Intake filter
- The gas and hydraulic oil occupy the same chamber but are separated by a piston, diaphragm, or bladder.
- When circuit pressure rises, incoming oil to the chamber compresses the gas.
- When circuit pressure drops off, the gas in the chamber expands, forcing oil out into the circuit.
- Most gas-loaded accumulators are pre-charged with the compressed gas that enables their operation.
- A fixed-displacement pump will move the same amount of oil per revolution with the result that the volume picked up by the pump at its inlet equals the volume discharged to its outlet per revolution.
- This means that pump speed determines how much hydraulic oil is moved.
- Fixed-displacement pumps are commonly used for applications such as
- Power steering pumps
- Transmission pumps
- Variable-displacement pumps are positive displacement pumps designed to vary the volume of oil they move each cycle even when they are run at the same speed.
- They use an internal control mechanism to vary the output of oil usually with the objective of maintaining a constant pressure value and reducing flow when demand for oil is minimal.
- Gear pumps are widely used in mobile hydraulics because of their simplicity.
- They are also widely used to move fuel through diesel fuel subsystems and as engine lube oil pumps.
- Three types of gear pumps are used
- External gear
- Internal gear
- Two intermeshing gears are close-fitted within a housing.
- One of the gears is a drive shaft and this drives the second gear because they are in mesh.
- As the gears rotate, oil from the inlet is trapped between the teeth and the housing, and is carried around the housing and forced from the outlet.
- A spur gear rotates within an annular internal gear, meshing on one side of it.
- Both gears are divided on the other side by a crescent-shaped separator.
- When an external gear is in mesh with an internal gear, they both turn in the same direction of rotation.
- As the gear teeth come out of mesh, oil from the inlet is trapped between the teeth and the separator and is carried to the outlet and expelled.
- A rotor-gear pump is a variation of the internal-gear pump.
- An internal rotor with external lobes rotates within an outer rotor ring with internal lobes.
- No separator is used.
- The internal rotor is driven within the outer rotor ring. The internal rotor has one less lobe than the outer rotor ring, with the result that only one lobe is fully engaged to the rotor ring at any given moment of operation.
- As the lobes on the internal rotor ride on the lobes on the outer ring, oil becomes entrapped as the assembly rotates, oil is forced out of the discharge port.
- Vane pumps are also used extensively in hydraulic circuits.
- Truck power-assisted steering systems use vane pumps.
- A slotted rotor fitted with sliding vanes rotates within a stationary liner known as a cam ring. There are two types
- As the rotor rotates, centrifugal force moves the vanes outward.
- Fluid is trapped between the crescent-shaped chambers formed between vanes.
- The size of these chambers are continually expanding and contracting as the rotor turns.
- Oil from the inlet is trapped in the space between two vanes.
- As the rotor continues to turn, the chamber contracts until it is aligned with the outlet and the oil is expelled.
- This action repeats itself twice per revolution because there are a pair of inlet ports and a pair of discharge ports.
- This has the same principle as the balanced version, with the exception that the operating cycle only occurs once per revolution because it has only one inlet and one outlet port.
- The disadvantage of the unbalanced vane pump is the radial load caused by high pressure that is acting on the discharge side of the rotor and none on the inlet side because the inlet oil is under little or no pressure.
- There are a wide variety of piston pumps, beginning with the most simple and including some of the more complex pumps used in hydraulic circuits.
- There are three general types of piston pump
- Plunger pumps
- Axial piston
- Radial piston
- Plunger-type pumps are seldom found on hydraulic circuits, but the latter two are used on systems that demand high flow and high-pressure performance.
- A bicycle pump is an example of a plunger pump as are the fuel hand-priming pumps used on many diesel fuel systems.
- A plunger reciprocates within a stationary barrel. Fluid to be pumped is drawn into the pump chamber formed in the barrel on the outward stroke of the plunger.
- This fluid is then discharged on the inboard stroke of the plunger.
- A rotating cylinder with piston bores machined into it rides against an inclined plate.
- The pistons are arranged parallel with the pump drive.
- The base of each piston rides against a tilted plate known as a swashplate or wobble plate which does not rotate.
- They provide a method for controlling the tilt angle of the swashplate.
- Fluid is charged to each pump element as the piston is drawn to the bottom of its travel.
- As the cylinder head rotates, the piston follows the tilt of the swashplate and is driven upward forcing fluid out of the discharge port.
- Radial piston pumps are capable of high pressures, high speeds, high volumes, and variable displacement. However, they cannot reverse flow.
- Radial piston pumps operate in two ways
- Rotating cam
- Rotating piston
- Valves are used to manage flow and pressure in hydraulic circuits.
- There are three basic types of valves used in hydraulic circuits.
- Pressure control
- Directional control
- Volume (flow) control
- Directional control valves direct the flow of oil through a hydraulic circuit. They include
- Check valves
- Rotary valves
- Spool valves
- Pilot valves
- A check valve uses a spring-loaded poppet. It permits flow in one direction and prevents flow in the other.
- A rotary spool turns to open and close oil passages. Rotary valves are commonly used as pilots for other valves in systems with multiple sub-circuits.
- A sliding spool within a valve body to open and close hydraulic circuits. Spool valves are used extensively in hydraulic systems and automatic transmissions.
- Pilot valves may be controlled mechanically, hydraulically, or electrically.
- Hydraulic actuators convert the fluid power from the pump into mechanical work.
- A hydraulic cylinder is a linear actuator.
- A hydraulic motor is a rotary actuator.
- Hydraulic pressure is applied to only one side of the piston.
- Single-acting cylinders may be either
- Outward-actuated When an outward-actuated cylinder has hydraulic pressure applied to it, the piston and rod are forced outward to lift the load. When the oil pressure is relieved, the weight of the load forces the piston and rod back into the cylinder.
- Inward-actuated When an inward-actuated cylinder has hydraulic pressure applied to it, the rod is pulled inward into the cylinder.
- One side of a single-acting cylinder is dry. The dry side must be vented so that when oil pressure on the pressure side is relieved, air is allowed to enter, preventing a vacuum.
- A ram is a single-acting cylinder in which the rod serves as the piston.
- Double-acting cylinders provide force in both directions.
- Pressure is applied to one side of the piston to either extend or retract the cylinder the oil on the opposite side returns to the reservoir.
- Double-acting cylinders may be balanced or unbalanced.
- Balanced double-acting cylinder
- The piston rod extends through the piston head on both sides, giving an equal surface area on which hydraulic pressure can act.
- Unbalanced double-acting cylinder
- A piston rod is located on one side of the piston. There is more surface area on the side without the rod because the rod occupies part of the space on the other side.
- Vane-type cylinders may be found in some much older hydraulic systems.
- A vane-type cylinder provides rotary motion.
- Double-acting vane-type cylinders can be used in applications such as backhoes because they enable a boom and bucket to swing rapidly from trench to pile.
- An alternative to one double-acting vane cylinder for this application would be a pair of opposing cylinders.
- The function of hydraulic motors is the opposite of hydraulic pumps
- It draws in oil and displaces it, converting mechanical force into fluid force.
- Oil under pressure is forced in and spilled out, converting fluid force into mechanical force.
- There are three categories of hydraulic motors
- Gear motors
- Vane motors
- Piston motors
- All hydraulic motors rotate, driven by incoming hydraulic oil under pressure.
- An external-gear motor is driven by pressurized hydraulic oil forced into the pump inlet, which acts on a pair of intermeshing gears, turning them away from the inlet, with the oil passing between the external gear teeth and the pump housing.
- An internal-gear motor is similar to an internal-gear pump. The motor drive shaft is connected to the inner rotor.
- The hydraulic fluid has to be conveyed to various components.
- Mobile hydraulic equipment uses hoses as hydraulic conductors because they
- Allow for movement and flexing
- Absorb vibrations
- Sustain pressure spikes
- Enable easy routing and connection on chassis
- The size of any hydraulic hose is determined by its inside diameter.
- This is sometimes indicated as dash size in 1/16-inch increments.
- Each dash number indicates 1/16 inch,
- a 4 dash hose would be equivalent to 4/16 inch or 1/4 inch.
- Dash size Nominal diameter
- 10 5/8 inch
- 12 3/4 inch
- A large-diameter internal hose has to be stronger to sustain the working pressures of a hydraulic circuit.
- Another consideration for hose selection is that the hose must be compatible with the hydraulic fluid used in the system.
- There are four general types of hoses used in hydraulic circuits
- Fabric braid
- Single-wire braid
- Multiple-wire braid (up to 6 wire braid)
- Multiple-spiral wire (up to 6 wire spirals)
- Hydraulic hose couplers (also known as connectors and fittings) are made of steel, stainless steel, brass, or fiber composites.
- Hose couplers or fittings can either be reusable or permanent.
- Hose fittings are installed at the hose ends and the mating end consists of either a nipple (male fit) or socket (female fit).
- Adapters are separate from the hose and are used to couple hoses to other components such as valves, actuators, or pumps.
- These fittings are crimped or swaged onto the hose.
- When a hose fitted with permanent hose fittings fails, the hose must be replaced either as an assembly or one must be made up using stock hose cut to length fitted with either crimp-type or reusable fittings.
- Reusable fittings are common in truck shops because a hose assembly station, some stock hose, and an assortment of reusable fittings can replace many of the hundreds of different types of hose used on various OEM truck chassis.
- When a hose with reusable fittings wears out, the fittings can be removed and assembled onto new stock hose.
- Reusable fittings are usually screwed onto hose, although some types of low-pressure hose may use press fits.
- Sealing fittings
- Fittings can be sealed to couplers using the following
- Tapered threads
- Nipple and seat (flair)
- When making hydraulic connections, ensure that the coupler fittings are compatible with each other.
- Adapters are separate from the hose assembly. They have the following functions
- To couple a hose fitting to a component
- To connect hydraulic lines in a circuit
- To act as a reducer in a circuit
- To connect a pair of hoses on either side of a bulkhead
- Separation of a fitting and hose at high pressure can be dangerous!
- Never reuse a suspect fitting and observe the manufacturer assembly procedure to the letter.
- When making hydraulic connections, the following guidelines should be observed
- Torque the fitting on the hose, not the hose on the fittings.
- Couple male ends before female ends.
- Ensure the sealing method of each fitting to be coupled is the same.
- Use 45- and 90-degree elbows to improve hose routing.
- Use hydraulic pipe seal compound only on the male threads, and on thread-seal unions.
- Use two wrenches when tightening unions to avoid twisting hose.
- Never over-torque hydraulic fittings.
- When tightening the fittings on a pair of hydraulic couplers, always use two wrenches to avoid twisting hoses or damaging adapters.
- Pipes used in hydraulic circuits are generally made from cold-drawn, seamless mild steel.
- They should never be galvanized because the zinc can flake off and plug up hydraulic circuits.
- Tubing can also be used.
- It has the advantage of being able to sustain some flex hence its use in vehicle brake systems.
- Tubing should be manufactured from cold-drawn steel if used in moderate-to-high-pressure circuits.
- When used in low-pressure circuits, copper or aluminum tubing may be used.
- 45 degrees (SAE standard -- Society of Automotive Engineers)
- 37 degrees (JIC standard -- Joint Industry Committee)
- Inverted flare
- A 45-degree flare is formed inside of the fitting.
- Two-piece flare
- A tapered nut aligns and seals the flared end of the tube.
- Three-piece flare
- A three-piece flare fitting consists of a body, sleeve, and nut and fits over the tube. The sleeve free-floats, permitting clearance between the nut and tube and aligning the fitting. When tightened, the sleeve is locked without imparting twist to the flared tube.
- These fittings use a wedge-type sleeve that, as the sleeve is tightened, is forced into the tube end, spreading it into a flare.
- Never attempt to cross-couple SAE and JIC fittings.
- The result will be to damage both.
- Ferrule fittings
- Consist of a body, a compression nut, and a ferrule.
- A wedge-shaped ferrule is compressed into the fitting body by the compression nut, creating a seal between the tube and the body.
- Compression fittings
- These are used with thin-walled tubing and are sealed by crimping the end of the tube to form a seal.
- O-ring fittings
- The principle is similar to ferrule-type fittings except that a compressible rubber compound O-ring replaces the ferrule.
- As the fitting nut is torqued, the O-ring is compressed, forming a seal between the tube and the fitting body.
- Several different types of O-rings are used, including round section, square section, D-section, and steel-backed.
- When hydraulic lines have to be frequently connected and disconnected, a quick release coupler is used.
- A quick coupler is a self-sealing device that shuts off flow when disconnected.
- Quick-release couplers consist of a male and female coupler. There are four types
- Double poppet.
- Sleeve and poppet
- Sliding seal
- Double rotating ball
- Hydraulic fluids used in truck hydraulic systems may be
- Specialty hydraulic oils
- Transmission oil
- Always check when adding to or replacing hydraulic oil.
- Synthetic hydraulic oils are commonly used in todays hydraulic circuits because they have wider temperature operating ranges and offer greater longevity.
- Hydraulic oils must
- Act as hydraulic media to transmit force
- Lubricate the moving components in a hydraulic circuit
- Resist breakdown over long periods of time
- Protect circuit components against rust and corrosion
- Resist foaming
- Maintain a relatively constant viscosity over a wide temperature range
- Resist combining with contaminants such as air, water, and particulates
- Conduct heat
- Truck hydraulic circuits are designed to run at high pressures and support high loads. It is essential that you work safely around chassis hydraulic equipment. Some basic rules
- Never work under any device that is only supported by hydraulics.
- A raised dump box or chassis hoist must be mechanically supported before you work under it.
- Just as when using a floor jack, you must use some means of mechanically supporting any raised equipment or components.
- Hydraulic circuit components can retain high residual pressures.
- The system does not have to be active for this to be a hazard.
- Ensure that pressures are relieved throughout the circuit before opening it up.
- Crack hydraulic line nuts slowly and be sure to wear both safety glasses and gloves.
- Fundamental hydraulic principles include Pascals Law, Bernoullis Principle, and how force, pressure, and sectional area are used in hydraulic circuits to produce outcomes.
- A typical simple hydraulic circuit consists of a reservoir, pump, valves, actuators, conductors, and connectors.
- Hydraulic pumps convert mechanical energy into hydraulic potential.
- Valves manage flow and direction through a hydraulic circuit.
- Actuators such as hydraulic cylinders and motors convert hydraulic potential into mechanical movement.
- Hydraulic oil is used to store and transmit hydraulic energy through a hydraulic system.
- ANSI and ISO graphic symbols are used to represent hydraulic components and connectors in hydraulic schematics.
- Maintenance procedures on truck hydraulic systems begin with ensuring the system is clean both inside and outside the circuit.
- Routine replacement of hydraulic fluid, sometimes accompanied by system flushing, is recommended to minimize system malfunctions and downtime.
- Hydraulic circuit testers are used to analyze hydraulic circuit performance.
- A hydraulic tester consists of flow gauge, pressure gauge, temperature gauge, and gate valve.
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