Controlling Speed

There are many ways to control the speed of a hydraulic ram or motor.
We could use a pump that delivers a variable flow (variable piston or vane pump)
The easiest way is to fit a flow control valve but the question comes where do you fit it?
Meter out: This is where a valve is fitted to each leg of the mover. The arrow for free flow should point towards the mover port. The flow is restricted on the return leg back to the control valve. This will prevent the load running ahead of the oil supply and keep the system stiff. However if screwed down too far can cause some intensification on the annular side of the ram.
Meter in: Good when the mover is pushing against a load but not if the load is trying to pull the ram. Imagine pushing a car up a hill. The best place to push is behind the car. As the car reaches the summit you need to move to the front to stop the car running away. The valve should be fitted with the free flow arrow pointing away from the mover towards the control valve.
Bleed off: This can be fitted on any leg of the mover or the main pressure line.
The valve is piped to tank and bleed oil off the main flow. This can be problematic and will not give a wide range of speed control. One main benefit is that it is less prone to generate heat.
Flow control on Pressure inlet: The valve would be a simple needle valve type.
Will cause heat generation. Excess oil will pass across the relief valve.
If you are unsure what is the best way for your system please send me an email.
I will write more on this subject including, pressure and temperature compensation and Load Sensing.
See more on www.hydraulicbrain.com
Cheers
Bob