Testing Hydraulic Pressure?

keeney · Apr 26, 2004

My 410 loader has always seemed a bit underpowered. I was using it the other day to load sand to prepare the floor of my new garage and I was uanble to sccop a full heaping bucket out of the pile without pushing and pulling the tractor back ond forth a bit.

Is there an easy way to test the hydraulic pressure?

Is there a good way to tell if a lack of pressure is due to pump performance?

I am tempted to try shimming the relief valve as mentioned in a previous thread, but if its the pump, it probably would not help.

Does the SCV have its own relief valve?

- Rick

Soundguy · Apr 26, 2004

Test the pressure, and then see how that measures up to the pumps specs.. if you are sufficiently below spec.. either it is reliefing too soon.. or the system isn't developing enought working pressure to beginwith.

Soundguy

OkieG · Apr 27, 2004

Is there an easy way to test the hydraulic pressure?
Testing is easy. The hard part is finding a pressure gauge. I found one at a tool supply co. Use a piece of hyd. hose to connect the guage to a hyd. quick connect the right size for your tractor. Once you get a gauge, the JD parts guys can find the right quick connect and put the pieces together for you. Plug it in to your FEL quick connects (one at a time) and activate the line with the SCV lever. Read the pressure directly from the gauge.

 Is there a good way to tell if a lack of pressure is due to pump performance? 
Often, you can hear the pressure relief valve going into bypass at max pressure.

 I am tempted to try shimming the relief valve as mentioned in a previous thread 
Definitely do not do this until you have checked system pressure. You don't want to blindly shim the relief valve. Hyd. pumps will not tolerate significantly more than their rated pressure before breaking. That would be a several hundred dollar mistake. I know, because I tried shimming to a few hundred psi above rated max. Pretty stupid. Pump broke almost right away.
On the other hand, if your system pressure is low, shimming can bring it right up to spec. Did I mention, I wouldn't shim past rated max.?

 Does the SCV have its own relief valve?
On my 1997 vintage 855, the SCV relies on the main system relief valve to limit pressure. Your tractor is probably that way too.

OkieG

kennyd · Apr 27, 2004

Rick, I made a tester for about $25.00. I got a liquid-filled gauge and a 1/4" x 12" hose from the SurplusCenter and a male QD from TSC. Plugged it in as described above, mine tested AOK.

Want to drive to Maryland to borrow it?

Kenny

JerryG · Apr 27, 2004

TSC has the gauge for about $20.

Hambone · Apr 27, 2004

Napa also has gauges, if not in stock usually next morning.

OkieG · Apr 27, 2004

I'm glad you and others have offered Keeney so many places to look for a guage. Finding one was the hardest part for me. JD lists a part # for the guage shown in their service manual, but it isn't stocked and I don't think Parts could even order it.
Found mine at Grainger supply, but I was supposed to have a tax number to buy it. The sales guy let me buy it anyway when he saw the disappointment on my face. I'd been all over looking for a guage, with no luck.

OkieG

keeney · Apr 27, 2004

Finding a gauge is not the problem. I know of at least three places to buy one, all on my way to and from work, one of which is open late on weekends. Plus the web.

The issue is how to determine if it is the relief that is dumping my pressure, or if it is the pump not being able to develop the pressure.

Can anything be inferred from pressure vs RPM at zero flow? I would assume that if it was the pump performance, the pressure would fall off more rapidly at low RPM's than if the relief was jsut set too low. In other words, the relief would not be affected so much by RPM's.

- Rick

OkieG · Apr 27, 2004

Can anything be inferred from pressure vs RPM at zero flow? I would assume that if it was the pump performance, the pressure would fall off more rapidly at low RPM's than if the relief was jsut set too low. In other words, the relief would not be affected so much by RPM's. 

The relief valve is not affected by RPM. Theoretically, the system pressure should not be affected by RPM either. On the other hand, flow (gal/min) is directly affected by RPM, since the pump turns in direct relation to engine speed.

On my tractor, I've noticed that max pressure drops off 50-100 psi at slow idle compared to full engine speed. Not sure what that means, but I think high flow allows the system to maintain a little higher pressure, even when the relief valve is open.

Anyway, system pressure should be measured at or near full engine RPM. That should be Test#1 for you. But, check the pressure at slower engine speeds too. If pressure is appropriate at high speed, and drops very little at slow speed, then I think your system is OK.
If system pressure is low, but pretty steady at all RPM, then shimming could help.
If system pressure varies a lot with RPM, then perhaps it's a pump problem.
I think that's the diagnostic sequence I would try. If it is still baffling after testing, then try JD or a hydraulics shop.

OkieG