Go BottomHydro relief pressure testing made simple
 | jeff r
Join Date: Jul 2003 Posts: 428 burton. michigan 
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2002-12-15 46148
Hey Guys,
I don't know how many of you guys are diagnostic tool minded, but my Kubota's B-2150's and Wood's 1006 FEL Loader that was dealer installed was acting a little "wimpy" on lift load capacity with the 54 inch bucket loading 10a stone. So I metioned to my brother after driving his Ford 1710 that his FEL seemed to lift more. He said the 1006 is a smaller loader but still should lift the front wheels off the ground very QUICK and EASY, plus a 54 inch bucket of 10A is not too heavy to lift without backing out of the pile. He asked me if I knew what the relief pressure was set at and had I ever checked it? Just being a mechanics helper for fun and Field Engineer in the metallurgy testing field for real, I said, "How and what do you use to check that?" He quickly rigs me up a 3000 pound capacity hydro gauge and hose and tells me to connect it to the loader's lift supply port on the control valve. I did it and found out my pressure was 350 pounds short of 1660 pounds. I reset the relief pressure valve to 1700 and VOILA...It works like a BIG DOG. Moral of the story is: a liquid filled gage and the proper hose and testing your relief pressure is a good and CHEAP tool to have around the shop. In the spring I am going to Check pressure on my backhoe. That gauge set-up is as handy as a hammer loop on your tool belt.
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 | Billy
Join Date: Oct 1999 Posts: 975 Southeast Oklahoma 
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2002-12-15 46151
That's pretty neat Jeff. Thanks for sharing.
Billy ....
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 | TomG
Join Date: Feb 2002 Posts: 5406 Upper Ottawa Valley 
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2002-12-16 46157
Yep, that a useful comment. Places like Northern Tool sell gauges for very little that are probably entirely adequate for most owners. Gauges from hydraulic suppliers tend to be pro quality and more pricey. People use old welding bottle gauges as well but they probably aren't as damped as an actual hydraulic gauge.
Here's some detail that might interest some people. A simple test point would be one replacing one of the loader cylinder hoses with a gauge. When the valve is operated the gauge would show the operating pressure.
However, sometimes it could be a little hard to know what actually is being tested. In this hook up, the gauge blind ends the circuit and a relief valve limits the operating pressure. However, on many tractors there would be two relief valves in the line (one in the loader valve and the tractor's system relief valve). Either relief valve could produce low readings. Many valves also have relief valves on the cylinder lines for shock loads. There could be three relief valves in the line.
Yep, bunches of diagnostics can be done with a gauge, although several with different scales may be needed. A t-fitting hook up will measure operating pressures produced by a load. A connection to a hydraulic manifold block will test the system relief valve alone. There often is a port on the 3ph for testing the 3ph cylinder pressure, because there's also a relief valve in most 3ph's. Gauges are available that measure flow as well as pressure, but they are fairly expensive.
In any testing, care should be taken not to run the engine when the pump is blinded ended. Without a relief valve in the system the engine probably couldn't be started, a reading taken and shut down fast enough to prevent damage to the pump.
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| jeff r
Join Date: Jul 2003 Posts: 428 burton. michigan
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2002-12-16 46182
You are most correct Tom, the guage would reflect the lowest of the two pressures and 1660 is lower than my tractors relief pressure. That means the loaders' relief valve opens first. ....
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| TomG
Join Date: Feb 2002 Posts: 5406 Upper Ottawa Valley
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2002-12-17 46216
Jeff: Yep that's what I'd do as well. If the pressure goes up when adjusting the loader or hoe valve relief then that's the culprit. If not, then there's a slightly more difficult problem of determining if the valve is broke another valve or maybe even the pump is weak.
Having said all this, I suppose I'll have to actually get a gauge. I've been trying to figure how to t-fit one into my PS line while avoiding purchasing an absurdly expensive fitting from NH for about a year now. I also think the relief valve on my hoe is weak. That's a similar hook up so it might get me motivated.
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| Morgan
Join Date: Jul 2003 Posts: 126 Albany, NY
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2002-12-22 46422
How do you set the relief pressure valve? Where is it? Why couldn't somebody just raise the relief pressure without testing it with a guage first?
Of course the engine has to be running at full RPM for all this to count, my rig has low pressure when the engine RMP is not running at full speed. To get full loader power the engine has to be revving all the way. ....
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| TomG
Join Date: Feb 2002 Posts: 5406 Upper Ottawa Valley
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2002-12-22 46427
Many but not all valves assemblies use for loader hoes etc. have their own relief valves. They usually are screw adjustable and the location would vary. Tractors also have their own relief valves. Mine is in a manifold block and is adjustable by shims.
Certainly a relief valve could just be cranked up without using a gauge. Relief valves are intended to protect components. There's no good way to ensure the setting isn't too high without a gauge and gauges are pretty cheap. The tractor's relief valve would provide adequate protection for most valves so from some perspective, a loader's relief valve could be cranked shut to rely on protection from the tractor's relief.
A small distinction about engine RPM: A basic idea in hydraulics is that loads produce pressure while pumps produce flow. Increasing RPM increases flow but not pressure directly. Only enough pressure to move a load can be developed. There is a but here. All pumps and cylinders have some internal leakage and the volume of leakage increases with pressure.
At high loads and low RPM's a pump's flow may be barely keeping up with the internal leakage and a loader would move very little. For that reason increasing RPM may lift a load that wouldn't move at low RPM, but it's really more flow rather than more pressure. It's a small distinction, but it might be interesting to some people.
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