Slowing Down Hydraulic Cylinder Movement 3

[jritz]

We have a hydaulic circuit with a single acting hydraulic cylinder (spring return) that moves against some resistance for a few inches - then is allowed to return via the spring. We want to slow down the outward movement of the cylinder when under pressure. We put a needle valve into the pressure circuit - but even when nearly closed , it does not slow the advancement of the cylinder. What do we need to do to make the cylinder movement slower and be able to vary the speed of the cylinder???

Thank You.

 

[jritz]

It is part of a test press.....the idea with this circuit is to slide test pieces back and forth to determine the coeffocient of friction and to determine wear. One cylinder pushs the piece "North" then the other pushes it "South" and so on. We are trying to slow down the rate which the cylinders extend. Right now the cylinder extend a too fast a rate.

I hope this helps.

jritz

 

[Oldhydroman]

I can see why you would want a pressure compensated flow control valve now – presumably you want the speed to remain constant regardless of the force needed to push the sample. You might, however, be disappointed with the performance of the simple pressure compensated flow control valves which are readily available. The speed regulation with varying pressure is OK for general use but I wouldn’t have a great deal of faith in it for materials testing. Similarly the speed regulation with varying temperature is also likely to be a bit underwhelming (and your oil is going to get quite hot with this method of control).

Basic pressure compensated flow controls also have a nasty characteristic where the cylinder always starts with a jerk. Explanation: while the cylinder is depressurised the compensator in the flow control valve opens fully, when you switch your DCV to pressurise the circuit the compensator needs a finite amount of time to get back to the proper regulating position – during this period the flow is too high hence the jerk. The jerkiness of the initial movement might spoil your test results.

You could go quite high tech and fit some proportional (or servo) valves, then use a stroke transducer on the cylinder and a closed loop speed control system (analogue or digital). But you might find that a simpler (yet still adequate) solution would be to fit a basic electronic speed controller to the electric motor driving your pump.

 

[MikeHalloran]

I'll second Oldhydroman's suggestion of a speed controller on the pump.


Mike Halloran
Pembroke Pines, FL, USA

 

[jritz]

We are gong to try and get a motor with speed controller for the pump as suggested. We will let you know how it goes.

Thank you everyone for your help on this!!!!

jritz

 

[hydtools]

Change to the Enerpac ZE3, 40in^3/min, in place of the ZE4, 60in^3/min. Or is that not slow enough?
How slow do you need?

Ted