6 Relief ValvesThe purpose of any relief valve is to protect the hydraulic system and its component parts from excessive pressure or damage.
7 Relief Valves Types Direct Acting- open / closed valves Pilot Operated- controls the main relief valve
8 Direct Acting Relief Valve OUTLETOUTLETINLETINLETCLOSEDOPEN
9 Direct Acting Relief Valve These valves are used mainly where volume is low, and for less frequent operations.They have fast response, making them ideal for relieving shock pressure.They are often used as safety valves to prevent damage to components.
10 Pilot Operated Relief Valve Because these valves don’t start to open until almost full-flow pressure, the efficiency of the system is protected-less oil is released.These valves are best for high-pressure, high volume systems.Although slower to operate than direct acting valves, the pilot operated relief valve keeps system oil at a more constant pressure while releasing oil
12 Constant Reduced Pressure Valves They supply a fixed pressure regardless of main circuit pressure. (So long as it is higher)
13 Constant Reduced Pressure Valve VALVE OPEN, NOT OPERATINGVALVE PARTLY CLOSESTO REDUCE PRESSUREFROM MAIN CIRCUITTO SECONDARY CIRCUIT
14 Fixed Amount Reduction Valves They supply a fixed amount of pressure reduction, which means that it varies with the main circuit pressure.For example,the valve might be set to give a reduction of 500 PSI. If system pressure was 2000 PSI, the valve would reduce pressure to ________ PSI.
16 Pressure Sequence Valves They are used to control the sequence of flow to various branches of a circuit.Usually the valves allow flow to a second function only after a first has been fully satisfied.
18 Unloading ValveThis valve directs pump output oil back to the reservoir at low pressure after system pressure has been reached.They may be installed in the pump outlet line with a tee connection.
19 Valve Types Pressure control valves Directional control valves Volume control valves
20 Directional Control Valves Direct the flow of oil in the systemTypes of valves- Check valves- Rotary valves- Spool valves- Pilot controlled poppet valves- Electro-hydraulic valves
21 Check Valves One way valves, only allow fluid to flow in one direction The valve is open by system pressureThe valve closes when inlet pressure dropsUsually installed in oil line
22 Rotary ValveTo ReservoirFrom WorkFrom PumpTo WorkThis valve allows pressurized oil from the pump to enter one port, flow through the valve, and out another port to the work
23 Rotary ValveThis valve also allows oil from another working port to flow through the valve and return to the reservoir.To ReservoirFrom WorkFrom PumpTo Work
24 Rotary Valves Used as pilot valves to direct flow to other valves Can be modified to operate as two, three, or four way valvesDone by relocating parts, altering passageways, or adding and removing oil routes
25 Spool Valves Most common is open center and closed center Directs oil to start, operate, and stop actuating unitsDirt can cause these valves to stick or work erratically
26 Spool Valvesopen center allows fluid to flow thru the center when in neutral and return to tankClosed center stops the flow of oil in neutralUsed as a control valves
29 Pilot Controlled Poppet Valves May be mounted close to the function it controlsEliminates the need for routing hydraulic pipes and hoses over long distances for every control functionReduces valve leakage (i.e. cylinder drift)Adjustable to vary amount of oil flow
30 Electro-Hydraulic Valves Actuated by an electric solenoid+ BATTERYROCKERSWITCHSOLENOIDTORESERVOIRFROMPUMP+ BATTERYROCKERSWITCHSOLENOIDTORESERVOIRFROMPUMP
31 Valve Types Directional control valves Pressure control valves Volume control valves
32 Volume Control Valve Types Flow control.Flow divider.
33 Flow Control ValvesRestricts flow in or out of the component whose speed is being regulated.These valves are noncompensated.
34 Bypass Flow RegulatorThis valve works by diverting flow away from the component whose speed is being regulated.These valve are usually compensated.BYPASSOUTLETFULL FLOW TO BYPASS
35 Volume Control Valve Types Flow control.Flow divider.
36 Priority Flow Divider Allows oil to feed two different circuit. Example,steering circuit and loader circuit.Pump output 10 gpm.Steering 2 gpm.Loader 8 gpm.PRIORITYOUTLETSECONDARYFIXED ORIFICEINLETFROMPUMP
37 Proportional Flow Divider OUTLET #1OUTLET #2INLETDivides a single flow of oil to two circuits.Can divided oil flow in ratios from to
38 Hydraulic Pumps The pump is the heart of the hydraulic system. The pump is the generating force of the hydraulic system, it creates the flow of fluid which supplies the whole circuit.Pumps convert mechanical energy to hydraulic power
39 Pump Classification Two classifications of pumps Fixed Displacement Variable Displacement
40 Types Displacement Fixed -Moves the same volume of fluid with each cycle
41 Variable Displacement Pumps Changing Displacement- this is accomplished by changing the angle of the swashplate.Swash Plate Positioning - The position is controlled by one of two ways.- A small hydraulic cylinder called a “servo”- A spring loaded cylinder called a “pressure compensator”
44 Gear Pumps Simple Design. Economical. Fixed Displacement. Used as charging pumps for larger system pumps.
45 Gear Pump Side PlatesSome gear pumps are equipped with pressurized plates on both side of the gears. These plates are used to prevent cavitation. The plates seal tightly when the pump is under a load and relax when there is no load.
46 Internal Gear PumpsPump HousingInletOutletSeparator(fixed)Outer RingGearInternal GearThe internal gear is the drive gear, which is meshed with the outer ring gear and traps fluid between the gear teeth on both gears and the separator, which is fixed.
47 External Gear PumpInletOutletPump HousingDrive GearIdle GearOil is trapped between the gear teeth and flows around the outer perimeter of the pump housing, not through the middle of the meshing gears.
48 Gear Pump Advantages Most widely used. Easiest to manufacture. Produces a large volume of oil for its size.Tolerant to dirt.Inexpensive to manufacture.
49 Gear Pump Disadvantages Noisier than other types of pumps.Fixed displacement only.
50 Vane Pumps Balanced Vane Pump - Fixed Displacement only. - Equalized force increases bearing life.Unbalanced Vane Pump- Either Fixed or Variable Displacement.- Frequent bearing failure.
51 Balanced Vane PumpPRESSUREHEREINLETROTOROUTLETPRESSUREHEREDRIVESHAFTBalanced pumps are preferred because they allow an even load of oil around the circumference of the pump shaft, this reduces the wear on the pump.PUMP HOUSINGVANE
52 Unbalanced Vane PumpPRESSUREUNBALANCEDHEREOUTLETVANEAs the name implies only one side of the pump forces oil through, causing the oil load to shift to one side of the pump.INLET
53 Vane Pump AdvantagesQuiet.They are self compensating for wear.
54 Vane Pumps Disadvantages Not as tolerable to dirt as gear pumps.Low volume output.Low pressure output.
56 Radial Piston Pump (Rotating Cam) Pistons are driven outward to discharge oil by the shaft cam, they move inward to take in oil by the force of their springs.Normally designed as a 4 or 8 piston model.SPRINGS
57 Radial Piston Pump (Rotating Piston) INLET PORTSAs the cylinder rotates pistons are thrown out against the housing by centrifugal force. A partial vacuum is created in the piston bores and oil flows into the inlet ports to fill the bores.ROTATINGCYLINDERFIXEDSHAFTPISTONPISTON BOREOUTLET PORTS
58 Radial Piston Pump (Rotating Piston) CYLINDERFIXEDSHAFTINLET PORTSPISTONPISTON BOREAs the cylinder keeps turning, the pistons are pushed back into the bores and force the oil out the ports on the outlet side.OUTLET PORTS
59 Axial Piston PumpsThe axial flow of fluid provides a more compact design and is the second most widely used pump in the industry next to the gear pump.Inline axial piston pump.Bent-axis axial piston pump
60 Axial Piston Pumps (Inline) SWASHPLATEPISTONDRIVESHAFTINLETROTATINGCYLINDERBLOCKPump can be variable displacement.Swashplate directs the intake and discharge of flow.Piston, draws and discharges the fluid.Cylinder block, holds the piston and rotates them from inlet to outlet ports.OUTLET
62 Axial Piston Pumps (Bent-axis) INLETOUTLETPISTONROTATING DRIVEMEMBERROTATINGCYLINDERBLOCKFixed displacement.Rotating drive member directs the intake and discharge of flow.Piston, draws and discharges the fluid.Cylinder block, holds the pistons and rotates them from inlet to outlet ports.DRIVESHAFT
64 Piston Pumps Advantages Able to withstand high pressure.Capable of variable displacement.
65 Piston Pumps Disadvantages Very low tolerance to dirt.More difficult to manufacture.Most expensive to manufacture.
66 Questions What are the three types of pumps? - Gear, Piston and Vane What will change the displacement of the piston pump?- Angle of the swashplateWhat is the purpose of the side plates in the gear type pump ?- These plates are used to prevent cavitation