6 Relief Valves The 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 OUTLET INLET CLOSED OPEN
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 OPERATING VALVE PARTLY CLOSES TO REDUCE PRESSURE FROM MAIN CIRCUIT TO 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.
15 Fixed Amount Reduction Valve FROM MAIN CIRCUIT TO SECONDARY CIRCUIT
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.
17 Pressure Sequence Valve INLET TO PRIMARY CIRCUIT INLET TO SECONDARY CIRCUIT CLOSED OPEN
18 Unloading Valve This 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 system Types 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 pressure The valve closes when inlet pressure drops Usually installed in oil line
22 Rotary Valve This valve allows pressurized oil from the pump to enter one port, flow through the valve, and out another port to the work To Reservoir From Work From Pump To Work
23 Rotary Valve This valve also allows oil from another working port to flow through the valve and return to the reservoir. To Reservoir From Work From Pump To 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 valves Done 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 units Dirt can cause these valves to stick or work erratically
26 Spool Valves open center allows fluid to flow thru the center when in neutral and return to tank Closed center stops the flow of oil in neutral Used as a control valves
27 Spool Valve (Stacked)
28 Spool Valve (Unibody)
29 Pilot Controlled Poppet Valves May be mounted close to the function it controls Eliminates the need for routing hydraulic pipes and hoses over long distances for every control function Reduces valve leakage (i.e. cylinder drift) Adjustable to vary amount of oil flow
30 Electro-Hydraulic Valves Actuated by an electric solenoid + BATTERY ROCKER SWITCH SOLENOID TO RESERVOIR FROM PUMP + BATTERY ROCKER SWITCH SOLENOID TO RESERVOIR FROM PUMP
31 Valve Types Directional control valves Pressure control valves Volume control valves
32 Volume Control Valve Types Flow control. Flow divider.
33 Flow Control Valves Restricts flow in or out of the component whose speed is being regulated. These valves are noncompensated.
34 Bypass Flow Regulator This valve works by diverting flow away from the component whose speed is being regulated. These valve are usually compensated. BYPASSOUTLET FULL 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. PRIORITY OUTLET SECONDARY OUTLET FIXED ORIFICE INLET FROM PUMP
37 Proportional Flow Divider OUTLET #1OUTLET #2 INLET Divides a single flow of oil to two circuits. Can divided oil flow in ratios from to
38 Hydraulic Pumps H The pump is the heart of the hydraulic system. H The pump is the generating force of the hydraulic system, it creates the flow of fluid which supplies the whole circuit. H 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 Plates Some 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 Pumps Pump Housing Inlet Outlet Separator (fixed) Outer Ring Gear Internal Gear The 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 Pump Oil is trapped between the gear teeth and flows around the outer perimeter of the pump housing, not through the middle of the meshing gears. Inlet Outlet Pump Housing Drive Gear Idle Gear
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 Pump PRESSURE HERE Balanced 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. INLET ROTOR OUTLET PRESSURE HERE DRIVE SHAFT VANE PUMP HOUSING
52 Unbalanced Vane Pump As 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 PRESSURE UNBALANCED HERE OUTLET VANE
53 Vane Pump Advantages Quiet. They are self compensating for wear.
54 Vane Pumps Disadvantages Not as tolerable to dirt as gear pumps. Low volume output. Low pressure output.
55 Piston Pumps H Radial piston pumps –Rotating cam. –Rotating piston. H Axial piston pumps –Inline axial. –Bent-axis axial.
56 Radial Piston Pump (Rotating Cam) CAM PISTON 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) As 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. ROTATING CYLINDER FIXED SHAFT INLET PORTS OUTLET PORTS PISTON PISTON BORE
58 Radial Piston Pump (Rotating Piston) H As 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 ROTATING CYLINDER FIXED SHAFT INLET PORTS PISTON PISTON BORE
59 Axial Piston Pumps The 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) Pump 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 SWASH PLATE PISTON DRIVE SHAFT INLET ROTATING CYLINDER BLOCK
62 Axial Piston Pumps (Bent-axis) Fixed 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. DRIVE SHAFT INLET OUTLET PISTON ROTATING DRIVE MEMBER ROTATING CYLINDER BLOCK
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 swashplate What is the purpose of the side plates in the gear type pump ? - These plates are used to prevent cavitation
67 HYDRAULIC MOTORS
68 Inlet Outlet Pump Housing Drive Gear Idle Gear Hydraulic Pump and Motor Drive Gear Motor Housing Inlet Outlet Idle Gear A pump drives its fluid, while the motor is driven by its fluid.
70 Hydraulic Motors A motor is a rotary actuator that rotates in a full circle. The work output of a motor is called torque. They convert hydraulic energy to mechanical energy.
71 Hydraulic Motors Fixed displacement motors- have variable speed but fixed torque Variable displacement motors- have variable speeds and torques