Proportional directional valves
Proportional directional valves
(OP)
Hi all, Could anyone familiar with these valves (Hytos in this case) help me figure out why the following happens: I have a hydraulic circuit where the principal components are: pump, Hytos proportional directional valve with closed center, a sequence valve which will actuate a cylinder (on extention) and when the cylinder reaches stroke end, the gear motor starts running (flow is now being diverted to it by the sequence valve). However, when doing the inverse procedure, when I move the valve past its center, therefore starting the retraction stroke of the cylinder( as the proportional control is turned from full flow paralel paths, to center and then moving towards cylinder retraction (crossed paths), the motor will start running albeit at a slower speed untill the cylinder is completely retracted and the gear motor then stops. I know its related to the differences between a proportional valve and an on/off one, but I just can't put my finger on it.
Thanks
Thanks





RE: Proportional directional valves
Keith Cress
Flamin Systems, Inc.- http://www.flaminsystems.com
RE: Proportional directional valves
thanks
RE: Proportional directional valves
RE: Proportional directional valves
FAQ238-1161: This is how to post pictures in your post.
Keith Cress
Flamin Systems, Inc.- http://www.flaminsystems.com
RE: Proportional directional valves
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RE: Proportional directional valves
Bud Trinkel, Fluid Power Consultant
HYDRA-PNEU CONSULTING
RE: Proportional directional valves
BTW, the two directional valves that are shown on the schematics are set in a manifold. However, in this case only the proportional directional valve (closed center) is connected to the circuit.
Thanks for your tips :)
RE: Proportional directional valves
Correctly designed proportional valves run with a high pressure drop to make them more responsive, in this case the high pressure drop creates a back pressure that is high enough to open the sequence valve and start the motors turning. When the cylinder stops there is no oil flowing so the motor stops turning.
Your options are to increase the size of the proportional valve, limit the flow rate of the pump, slow the cylinder down, decrease the size of the motors so they need more pressure to rotate or increase the opening pressure of the sequence valve.
Whatever you do to make the retraction operation work will effect the extension operation.
The schematic shows a pressure test point on the input side of the sequence valve. Put a pressure gauge and you will see the pressure rise quite high when the cylinder retracting.
Good luck
Regards
Adrian
Hydraulic System Engineering Consultant
RE: Proportional directional valves
Keith Cress
Flamin Systems, Inc.- http://www.flaminsystems.com
RE: Proportional directional valves
Thank you all
RE: Proportional directional valves
Going this route, cylinder extend stays the same, cylinder retract speed can be increased and the bottleneck can be hopefully eliminated. As Hydro mentioned there are other options but they affect both extend and retract. Maytyag
RE: Proportional directional valves
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Bud Trinkel, Fluid Power Consultant
HYDRA-PNEU CONSULTING
RE: Proportional directional valves
Kebecano...you are welcome.
Posts like yours are few and far between. It's a pleasure to help.
Another possible solution would be to change the oil to one with a lower viscosity. That would reduce the pressure drop.
You say the motor turns slowly, that means the bleed off to through the sequence valve is quite low. It won't take much to stop it happening. The schematic shows a flow meter, can you use that to tell how much flow the motor is seeing when the cylinder is retracting?
Have you noticed that the speed of the motor slows are the system gets warmer?
Regards
Adrian