M925A2 Hydraulic Specs (Flow Rate and Bypass Relief Pressure)?

[74M35A2]

Hi all. Seeking the hydraulic flow rate and bypass/relief valve pressure setting in the hydraulic system of the M925A2. WildChild467 has found the minimums for me, which are spec'd out at 800r's engine speed, but they are minimum test specs.

I am converting over to 24V solenoid type hydraulic valves for my front winch and the same winch which I am soon installing in the rear, and therefore need to know how to size them appropriately. I have seen 25gpm mentioned on the pump, but is this at 2000rpm engine speed? Also I believe the hydraulics of the winch up front simply go into bypass/relief if the winch is over-loaded, so I also need to know the approximate pressure at which this occurs. There is a significant cost difference between 3000psi and 4000psi 24VDC solenoid valves.

Thanks, and apologies if I have missed it in the TM's or other posts.

 

[Ddmk18]

I am interested in this also. If you don't mind what did he come up with for minimum rates thank you.

 

[74M35A2]

Do I suck this bad? Maybe. I absolutely can not find the hydraulic relief pressure for the front hydro winch system on the M925(A2). I presume the winch is protected by a pressure relief valve rather than a shear pin, but can anybody help to locate this pressure setting? I believe the pressure relief to be within the mechanical control valve, where the return line is located. I can put a pressure gauge in-line with my front winch now, and tie the cable to a tree base and load it up till it goes into bypass and take the pressure reading, but if my existing relief valve/spring is weak or otherwise not correct, then I would hate to use that figure in setting up my new solenoid system. Best way would be to use a tension load cell also, and dial it in so the winch does pull 20,000lbs on the first drum layer.

I can find the pressure relief data for the M936 wrecker bed hydro system (1600psi-1800psi range), but I don't want to simply assume it is the same. The front winch hydro pressure should be adjusted to that the front winch can not pull more than 20,000lbs single line. I have search TM's to the point where I am about to get fired from my job!

 

[Wildchild467]

I looked it up too trying to find it and saw the same thing. For conversation sake, it was about 1600-1800 PSI... but it seemed kind of vague. I looked in TM 9-2320-272-24-2 section 4-33 and the following page 4-34. This is what I found but I would like somebody to confirm this is correct because I am not sure:

 

[Ddmk18]

Thank you!!!!

 

[Wildchild467]

But is what I found in the TM correct? it seems vague... and how do you adjust the pressure relief valve on the truck?

 

[Ddmk18]

Seems correct to me. You can't adjust the pressure on the truck. The control valve has a built in relief valve that keeps the pressure between 1650-1850. If your not within those specs you have to replace the control valve or check other parts of the system for the problem.

 

[Wildchild467]

I also found in the TM that says the winch should not be operated when the engine RPM is over 1800 RPM. I'm not sure why. That would put your flow at 1800 RPM around 12 GPM. I also see that the the same hydraulic pump controls the front winch and the dump hoist on the M930's. If anybody else can confirm this, let me know. I know deuces a lot better than M939's, but I believe I am reading the TM's correctly.

 

[74M35A2]

I also found in the TM that says the winch should not be operated when the engine RPM is over 1800 RPM. I'm not sure why. That would put your flow at 1800 RPM around 12 GPM. I also see that the the same hydraulic pump controls the front winch and the dump hoist on the M930's. If anybody else can confirm this, let me know. I know deuces a lot better than M939's, but I believe I am reading the TM's correctly.

View attachment 524213View attachment 524214

The 1800rpm limit is likely due to the sizing of the pump vs control valve relief/return. The pump output hose is huge, and the relief valve/return port and hose size is tiny. All of that flow and pressure would be forced through the tiny relief valve/return port in the control, and likely overcome the system with too much volume and pressure. I did it, and now I have a leak at the control valve inlet hose connection from the pump. I SHOULD HAVE READ THE MANUAL !!!! That size pump covers the dump version of the truck also, which fills 2 large cylinders and maybe a little more appropriately sized.

 

[2old2humps]

the pressure relief is in the hyd control valve. it is not adjustable from the outside, but....... should you wish,you can remove the cap above the return line and shim the spring with the correct diameter washers to go were ever you dare on psi. there is is a seat under the spring. make sure it is returned to its correct position or you will have no pressure. remember when you go above 1800 psi you are above specs and things can break.