Hydraulic Circuit Design

Transcription

1 26/10/05 Hydraulics & Pneumatics Hydraulic Circuit Design M. S. Sham Prasad Asst. Professor Dept. of I&P Engg. National Institute of Engg, Mysore

2 Regenerative circuit : A Regenerative circuit is one in which pressurized fluid discharged from a component is returned to the system to reduce power requirements of the pump.

3 Flow from the rod end (Q r ) regenerates with the pump flow (Q P ) to provide a total flow rate (Q T ), which is greater than the pump flow rate to the blank end of the cylinder. The speed of extension is greater than that for a regular double-acting cylinder

4 Hydraulic power pack :

5 Regenerative circuit

6 Regenerative circuit

7 Speed during Extension (Regenerative speed): Q T = Q P + Q r i.e., Q P = Q T - Q r Q P = A P v Pext - (A P - A r ) v Pext solving, v Pext = Q P / A r

8 Load Carrying capacity during Extension: F load during extension for a regenerative cylinder is, F load = p A r rather then pa P due to same pressure acting on both sides of the piston.

9 Ratio of Extending and Retracting speeds: we have, v Pext = Q P / A r and v Pret = Q P / (A P - A r ) Therefore, v Pext / v Pret = (A P - A r ) / A r =(A P / A r ) - 1 If A P = 2 A r Then v Pext = v Pret

10 1. A double acting cylinder is hooked up in the regenerative circuit. The relief valve setting is 70 bars. The piston area is m 2 and the rod area is m 2. If the pump flow is m 3 / s, find the cylinder speed and load- carrying capacity for the a. Extending stroke b. Retracting stroke.

11 Extending Stroke: Cylinder speed, v P ext = Q P / A r (Regenerative Speed) = / = 0.29 m / s Load carrying capacity, F load = p A r = 70 * 10 5 * = N = 31.5kN

12 Retracting Stroke: Cylinder Speed, v P ret = Q / P (A P - A r ) = / ( ) = m / s Load carrying capacity, F load = p ( A P - A r ) = 70 * 10 5 ( ) = N = 80.5kN

13 2. A double acting cylinder is hooked up in the regenerative circuit. The relief valve setting is 100 bars. The piston area is twice the rod area. If the pump flow is m 3 / s, and regenerative speed is 0.25 m/s, find the piston area and loadcarrying capacity for the a. Extending stroke b. Retracting stroke

14 Regenerative cylinder speed, v p ext = Q p / A r Therefore Rod area, Ar = Q p / v p ext = / 0.25 = m 2 Piston Area, A P = 2 A r = 2* = m 2

15 Extending Stroke: Load carrying capacity, F load = p A r = 105 * 10 5 * = N = 67.2kN

16 Retracting Stroke: A P = 2 A r = m 2 Load carrying capacity, F load = p ( A P - A r ) = 105 * 10 5 * ( ) = N = 67.2kN

17 Application in Drilling Machine

18 Pump Unloading circuit : An unloading valve can be used to unload a pump The unloading valve opens when the cylinder reaches the end of its extension stroke because the check valve keeps highpressure oil in the pilot line of the unloading valve

19 The control signal for unloading valve is remote and obtained after the check valve whereas in Relief valve it is inside the valve.

20 Pump unloading Circuit L

21 Double Pump Hydraulic system ( Hi Lo circuit ) Two pumps, one high-pressure, low-flow pump and the other low-pressure, high-flow pump. Application in a punch press in which the hydraulic ram must extend rapidly over a large distance with very low pressure but high flow requirements.

22 During the short motion portion when the punching operation occurs, the pressure requirements are high due to the punching load. Since the cylinder travel is small during the punching operation, the flow-rate requirements are also low.

23 The circuit eliminates the necessity of having a very expensive high-pressure, high-flow pump. When the punching operation begins, the increased pressure opens the unloading valve to unload the low-pressure pump

24 The relief valve protect the high-pressure pump from overpressure at the end of the cylinder stroke.

25 The check valve protects the low pressure pump: From high pressure, which occurs during the punching operation. At the ends of the cylinder stroke, When the DCV is in its spring-centered mode.

26 Double Pump hydraulic system L P 1 P 2

27 Application of CounterBalance valve Used to keep a vertical cylinder in the upward position while the pump is idling. Lower the load gradually.

28 Counterbalance valve application L

29 Cylinder Sequencing circuit: Two cylinder(c 1 & C 2 ) have sequence of operation. Operation sequence is : C 1 + C 2 + C 2 - C is Extension of piston - is Retraction of piston

30 Cylinder sequencing C 1 + C 2 -

31 C 1 + C 2 + C 2 - Cylinder Sequencing

32 Cylinder sequencing C 1 +C 2 +C 2 - C 1 -

33 C 1 + Cylinder sequencing

34 C 1 + C 2 + Cylinder sequencing

35 C 2 - Cylinder sequencing

36 C 2 - C 1 - Cylinder sequencing

37 Problem : Design a sequencing circuit for operating two cylinders in sequence. The sequence of operations are C 1 +C 2 +C 1 - C 2 - Solution: Observe the cylinder 1 is extended and retracted first

38 C 1 +C 2 +C 1 - C 2 - Cylinder sequencing