I recently purchased a walk behind concrete saw with a hydraulic drive for the wheels. I don't have the ability for a cicuit diagram, but I'll try to verbalize it. I believe it is an open loop design. The pump has three lines to it,two on the end (one from the supply tank, the second to the valve assembly),the third line also returns to the resevoir. The valve body has four connections and a forward,reverse actuator. one connection from the pump, a second connection opposite goes to a filter and then to the resevoir, the two other lines go to the drive motor. So far basicly simple.

But aye!, here's the rub (sorry pirate humor, couldn't resist.

Between the pump output and the valve body there is a adjustable knob. My assumption is this is a variable flow control.

Finally the problem: I can adjust the control enough to work the engine, kill it, smoke the drive belt, etc...Since this doesn't seem right I must be missing something, but it appears factory design. If I wanted to control the flow to the drive motor, (variable speed?) shouldn't the valve be on the lines to the drive motor?

Hope you have some ideas, perplexed

From your description it appears you have a Pressure Compensated Piston Pump that is adjusted to a High Pressre on its Compensator Adjusting setup.

There should be an Adjusting Knob or Screw somewhere on the Pump, Usually near the Outlet End, that usually increases pressure when turned Clockwise.

If it was my pump I would try turning it Counter-Clockwise to reduce pressure. If that does'nt help the stalling you probably have a pump that has failed on stroke so it is now acting like a Fixed Volume Pump instead of reducing flow when the Flow Control is turned to a reduced flow condition.

It could be as simple as a crudded up Compensator Spool that is blocked from moving when pressure builds. Turning the pressure adjustment may allow it to break loose and start working again.

If you do get it working I would highly recommend you change the oil, run the machine for a short time , change the oil and do that about three times or until the drained oil starts looking like new oil. Then do the drain/new oil scenario about every 30 hours of running time to keep the circuit cleaner.

still confused, I thought I would add some photo's to clarify the valve and pump

still a little confused. Here's a photo of the valve body and variable valve.

I only see a smaal portion of the top of your pictures.

quote:

Pressure Compensated Piston Pump

I apologize for that, I will need to get a faster access for photos and I will try again

quote:

Pressure Compensated Piston Pump

Here's the valve photo

It is an Oilgear PVWH Pressure Compensaed pump. The rectangular body on top of the pump contains the Compensator spring and you set pressure with the Hex Bolt by loosening the Jamb Nut and screwing in to raise pressure.

The Adjusting screw looks like it is pretty far out which means it is seet for low pressure.

From your application I would guess the Compensator and/or the Pump are full of crud and some part that moves to reduce pump flow is not capable of moving due to contamination.

Changing oil is necessary but the pump will probably have to be taken apart and cleaned at least and maybe a lot more.

You can see all about the pump at this web site:
http://www.oilgear.com/components/pumps/variable/index.php
Links there will take you to some literature and if you can find it there will be a complete parts breakdown.

Try to find a part number on the pump since I notice there are a couple of similar pumps in this line that look like yours.

This pump was originally manufactured by HYDURA and Oilgear bought them out 10-15 years back so your part number may not match the Oilgear one. Oilgear's site has a link to contact them for information.

Bud, what's the 3rd line? A case drain?

Yes

Thanks Bud
You identification was right on the money. Found a tag, and after I removed the paint it was model # PVWO 6lsaycnnn. Looked on your link but it was not listed, I will have to do some more research. It will probably take some time to pull it apart for cleaning and inspection. Just a footnote - while looking old I believed it has less than twenty hours on it.
Gerritt

quote:

while looking old I believed it has less than twenty hours on it.
Gerritt

The amount of contaminants it consumes in your appliction means it must have excellent filtration and/or excellent sealing of the system or its life will not be long.