Week 3 1_hydraulics_valve3


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Week 3 1_hydraulics_valve3

  1. 1.  Pressure control valves (PCVs)  Directional control valves (DCVs; direct- and pilot-operated)  Flow control valves (FCVs)  Check valves
  2. 2.  To control and regulate pressure in hydraulic system  Types ◦ Pressure relief valve ◦ Pressure regulator
  3. 3.  connected with high-pressure and return low pressure lines.  used to limit the maximum operating pressure in the high-pressure lines. The relief valve consists mainly of a poppet, loaded by a spring. P T
  4. 4.  The poppet is pushed by the spring to rest against its seat in the valve housing. The spring pre-compression force is adjusted by a spring seat screw or by inserting distance rings.  The following formula is used to calculate the cracking pressure for this valve
  5. 5. PCV Normal position  Pressure control valve practically is used in every hydraulic system.  It is normally a closed valve whose function is to limit the pressure to a specified maximum value by diverting oil from pump flow back to the tank.  Refer to the circuit : When the motor is on and the control valve is un-actuated, the fluid pressure in the pipe line will increase. At the maximum pressure, the pressure relief valve will open and allow the fluid to return back to the tank Without the pressure relief valve the pipe line may explode or the pump damage.  If the valve is actuated, the piston will extend. When the piston fully extend the pressure will also increase and again the pressure relief valve will open.
  6. 6.  Reduce the output pressure to safe/usable pressure.  Automatically shuts off hydraulic flow at a certain pressure. A P T
  7. 7.  DCVs are used to start, stop, or change the direction of fluid flow.  The valves are specified by the number of connected lines (ways) and the number of control positions.  The control positions determine the way in which the lines are interconnected, and consequently the directions of fluid flow.
  8. 8.  E.g.  A 4/3 directional control valve is connected to the pressure line (P), return line (T), and cylinder lines (A and B). In its neutral position, the valve closes all of the four lines and the cylinder is stopped. By switching the valve to any of the other positions, the cylinder moves in the corresponding direction.
  9. 9.  Types: 1. 2 ports/2 way 2. 3 ports/2 way 3. 4 ports/2 way 4. 4 ports/3 way
  10. 10. ◦ 1 working port and 1 pressure port ◦ Control delivery by closing or opening the passage
  11. 11. Type of 2/2 Way Valve. (Normally Open and Normally Closed) 2/2 Way Valve (Normally Close) type 2/2 Way Valve (Normally Open) type
  12. 12. ◦ 1 working port,1 pressure port and 1 tank connection ◦ Control delivery  Normal position – P is closed and A to T is open  Actuated position – T is closed, flow from P to A
  13. 13. Type of 3/2 Way Valve. (Normally Open and Normally Closed) 3/2 Way Valve (Normally Open) type 3/2 Way Valve (Normally Closed) type
  14. 14. 3/2 Valve (Normally Closed) Use for single acting cylinder NORMAL POSITION ACTUATED
  15. 15. ◦ 2 working port (A, B), 1 pressure port and 1 tank connection ◦ Control delivery  Normal position – flow from P to B and A to T  Actuated position – flow from P to A and B to T
  16. 16. 4/2 Valve (PB Type )
  17. 17. 4/2 Valve (Lever type) NORMAL POSITION Use for double acting cylinder
  18. 18. 4/2 Valve (Lever type ) ACTUATED
  19. 19. The 4/2 way DCV used in previous circuit are sometime impractical since they continuously sending flow and pressure into hydraulic actuator. The should give a relief to the actuator, a NEUTRAL position should be used, where the actuator is not subjected to pump pressure. NEUTRAL POSITION 4/2 Valve 4/3 Valve
  20. 20. HYDRAULIC AND PNEUMATIC 4/3 Valve With Closed Neutral Position Closed Neutral Position: (1) The Pump is blocked. (2) The flow goes to Pressure Relief Valve. (3) The maximum allowed pressure of the system is set by the pressure relief valve.
  21. 21. HYDRAULIC AND PNEUMATIC 4/3 Valve With Tandem Neutral Position Tandem Neutral Position: (1) A desirable condition where the only pressure involve line resistance. (2) The power consumption is reduced. Is said to be UNLOADED. (3) Less energy wasted.
  22. 22. HYDRAULIC AND PNEUMATIC 4/3 Valve With Open Neutral Position Open Neutral Position: (1) A combination of a tandem and float neutral position. (2) A flow will return to the tank from the pump. (3) At the same time, A bit of flow might still be flowing (floating) at the actuator.
  23. 23. HYDRAULIC AND PNEUMATIC 4/3 Valve With Float Neutral Position Float Neutral Position: (1) A desirable condition for a circuit with motor, since it allow the motor to spin until fully stop. (2) This condition is said to allow the motor to float or spin freely without influence of pump. (3) Not using it may caused pressure increase at the motor, since spinning motor might give a resistance when the positioned is changed.
  24. 24. HYDRAULIC AND PNEUMATIC 4/3 Valve With Regenerative Neutral Position Regenerative Neutral Position: (1) A term used where the flow returning from actuator is feed back into the pressure line to give supplemental power.
  25. 25.  Also known as non-return valve  generally used to allow for free flow in one direction  prevent (obstruct) the fluid flow in the opposite direction  Type: ◦ Spring loaded ◦ Without spring
  26. 26. Check Valves in Circuit
  27. 27.  FCV is used to regulate speed  It limit the amount of flow in a main or branch hydraulic circuit  Types: ◦ Throttle valve ◦ One-way FCV
  28. 28.  Used to restrict the flow from either direction  AKA as needle valve.  A throttle valve control the flow rate in the circuit.  By controlling the flow rate, the speed of the actuator can be controlled. FCV: Throttle valve
  29. 29.  Restrict the flow in one direction while allowing a bypass in the opposite direction  Used to reduce the speed of cylinder movement 100%
  30. 30.  A one way FCV give a controlled flow direction from left to right (A) and a free flow in reverse (B)
  31. 31. END OF LECTURE