M939 Dump Truck adding valve body for snow plow

[Jim832904]

Trying to complete the project and having trouble with plumbing the tie in to the existing hydraulic system. Can't find any help in the TM's. Would like to know if the original pump is gear type direct displacement . Also would like to know if the dump body valve is spool open center or poppet type. My add on valve body is mounted above the RH side fuel tank and is a open center spool type with multiple sections . I want to control the plow hoist with a single hose on one section and plow angle with two hoses on another section.
My problem is getting pressure to the add on valve body. Have tried to T into the pressure and return = no pressure. Have tried to run pressurehose in series into existing valve, out to new valve and return to reservoir-this caused an over pressure and blew fluid out the first valve and made a mess. Not sure if any damage was done.
Thinking now about a 3 way diversion valve in the pump pressure line to supply either the dump body valve or the plow valve one at a time.
Am I on the right track?

 

[rangereter]

I wouldn't think you can use your return from the dump hoist valve like a "power beyond" function. You could use a diversion valve, but with an adjustable priority valve you would not have to manually change hyd. circuits. However, you would have to check flow rates for this type of application. T-ing into an open center system feed won't do any good with the fluid taking the path of least resistance. Have you checked the parts tm pump breakdown to verify pump type? (the tm may or my not break the pump down I realize)... I have not been into these particular systems, but I would be willing to bet it is just a gear pump.
Regards, Bob

 

[Jim832904]

Thanks Bob. I agree in all areas. Just got a manual diversion valve and will plumb it in as soon as the air gets back above the teens. I believe it is a gear style pump. Hoping the add on spool type valve body has nothing stuck inside. It was from an old municipal truck. Will let the forum know the end result and I'll have photos of the entire installation. It did require moving a few items.

 

[pa.rich]

Back when I plowed with a tandem axle dump, we had air pistons to raise and lower the blade. Would the compressor put out enough air to run the plow's ups and downs and power the angle pistons? Anybody utilize an air powered system?