pressure difference in hydraulic motors

[MHarryE]

ISO 46 is kind of thin for your low speed high torque app. It’s 40 to 50 cSt or the low end of SAE 20 engine oil (35 to 75 cSt). A 15W-40 engine oil is good for your application although in a harsh hydraulic app the viscosity enhancers will shear down over time so you end up with 15W-30. The common farm hydraulic fluids are 55 cSt at 40 and 9 cSt at 100 so its normal to have speed loss with temperature rise due to the viscosity drop.

 

[greenerdreams]

the valve is after the speed control, i tested pressure at the inlet before the speed control. I am understanding now that the aw46 is possibly not the best product but i can't find a crossover chart for the recommended vermeer vhf or philips hg. the interesting thing is that after maybe less than an hours use the motors will lose so much power that they will stall on almost any size branch(when fully operational it can take over a 12" tree easily). the more i mess with the control valve the more i think it may be the majority of the problem via large internal leaking. I would try a rebuild but getting parts has been a problem. I am going to try to identify the model so i can maybe get a replacement from surplus center for cheap just to see what happens.

 

[ddbackhoe]

the valve is after the speed control, i tested pressure at the inlet before the speed control. I am understanding now that the aw46 is possibly not the best product but i can't find a crossover chart for the recommended vermeer vhf or philips hg. the interesting thing is that after maybe less than an hours use the motors will lose so much power that they will stall on almost any size branch(when fully operational it can take over a 12" tree easily). the more i mess with the control valve the more i think it may be the majority of the problem via large internal leaking. I would try a rebuild but getting parts has been a problem. I am going to try to identify the model so i can maybe get a replacement from surplus center for cheap just to see what happens.

This site has more info than you really want but it is a very good one.

Hydraulic Systems and Fluid Selection
Choosing the Right Hydraulic Fluid

 

[oldnslo]

the valve is after the speed control, i tested pressure at the inlet before the speed control. I am understanding now that the aw46 is possibly not the best product but i can't find a crossover chart for the recommended vermeer vhf or philips hg. the interesting thing is that after maybe less than an hours use the motors will lose so much power that they will stall on almost any size branch(when fully operational it can take over a 12" tree easily). the more i mess with the control valve the more i think it may be the majority of the problem via large internal leaking. I would try a rebuild but getting parts has been a problem. I am going to try to identify the model so i can maybe get a replacement from surplus center for cheap just to see what happens.

Greener,
I presume this unit worked well for you in the past and this problem is something new or has it never worked well?

before you try and rebuild the valve can you either take a couple more pressure readings or temperature readings to try and identify the source of the heat.

I suggest starting with the system cold and monitoring the temperature of the different components. If the valve shows rapid temperature climb Vs the other components that is where I would start looking for problems & or perform more tests to further isolate the problem area. Possible some linkage is not shifting the valve one way, did a spring keeper come loose, etc..

Another option is install multiple test points or gauges in the system to monitor pressure losses. I.e. one at the inlet to the valve in question and one at the port feeding the motors.