Hydraulic System Surges

[jswiontek]

I'm a novice when it comes to hydraulics so this may be a silly question but what are some possible causes for a hydraulic system to surge? I have flow coming into a main motor, then taking the exhaust from that motor and reducing the flow with a priority flow divider and sending that regulated flow to a fan motor. We have taken the fan motor out of the loop and the system operates with no problem so it has something to do with the fan motor. All specs are more than adequate. I don't know what could be wrong with the fan motor to cause the system to surge.

 

[MikeMilburn]

Try putting a 200psi check valve in the line from the fan motor to tank, it sounds as if the fan motor is running away as far as speed goes....Mike

 

[automatic2]

It's likely a harmonic that is set up between main motor and fan motor, with the flow divider acting as an amplifier. Depending on your valve, you may be able to run it in a pressure reducing configuration.

 

[budt]

Is the Flow Divider sized correctly? If the divider is capable of greater flow than it is seeing its spring loaded spool could be moving too far as it sends flow to the fan motor then moving to far back to reduce flow. Once it starts hunting it will keep doing so and cause surges.

I have put spacers to reduce spool movement and eliminate hunting but this is a trial and error situation.

Your best bet would be to use a motor type flow divider with unequal flow sections. This type flow divider also waste's less energy so the system runs cooler. It only works correctly if flow is constant.

Bud Trinkel
Certified Fluid Power Engineer
HYDRA-PNEU CONSULTING, INC.
812-853-3234
fluidpower1@hotmail.com