Hydraulic pump - Capacity??

chriswheeler · Jul 4, 2014

Winston, fork lifts have been using a gage to weigh loads for decades now, here is how it works. If you do install a gage, be sure to use one that goes to at least 2400 psi or you can blow up the gage. There is little or no pressure on a unloaded hyd system until it gets a load or resistance. When resistance is encountered, such as a load on a lift truck, or on a tractor FEL, the positive displacement pump builds pressure until it overcomes the load or the load is removed and the hyd circuit is opened. If a gage was placed into the lift hyd pressure line on your tractor FEL, pressure is low just lifting the bucket and arms. Go get a scoop of rock and notice that the hyd pressure increases proportional to the load lifted. Remove the load, gage falls back to just what it takes to lift the empty bucket and arms. Yanmar tractors operate between 2000-2200 psi only when a load is applied to that hyd circuit. That is why it is so important that the flow be returned to the high pressure line when the FEL is removed. If not, the pump will over pressurize and shear the drive key or blow up the pump. When the flow of the hyd pump is not being used, the pressure side of the pump discharge is simply returned to the sump in the transmission and recirculated. Also be aware that there are relief valves installed in the valve body of the 3 point, and usually in the joystick on a FEL to prevent the full 2200 psi ever reaching the lift or the bucket. Part of installing a new FEL is setting the relief valve as to not tip over the tractor with overloading.

Chris

winston1 · Jul 5, 2014

Test results are in. I teed in off the power beyond on my loader control valve. Woods mower weighs in at 503lbs per Woods.

Raised position with tractor idling at 700rpm the low pressure gage registers 40psi.

Raised position with tractor running 1150rpm the low pressure gage registers 100psi.

Raised position with tractor running 2000rpm (not sure) the high pressure gage registers 250-300psi.

Tractor running 2200rpm with mower in process of raising the high pressure gage registers 1200psi

I have checked my relief valve pressure in days past and I know it was in the 2100 to 2200psi range.

No picture to support it but when idling at 700rpm and turning the steering wheel (power steering) the pressure drops from 40psi to around 20psi. The diverter valve working.

I suppose nothing accomplished here but I find this sort of thing interesting. :thumbsup:

normde2001 · Jul 5, 2014

Yep, me too.

kenmac · Jul 6, 2014

winston1 said:
Nice to be at the stage in life you can just do whatever you want to when you want too. Big plus is still being able too.

1 day I'll get there. I hope ! As a business owner, (me) I don't know how to do it.Sell out,close down, etc, .As always, I enjoy reading your research

normde2001 · Jul 6, 2014

Yup, Winston, I'm having a tough time wrapping my brain around this type of pump output. So, fact is, the only danger from a broken high pressure line is if it is under a load.

bumpyrider · Jul 25, 2014

I think Chris kinda covered it, but I wanted to toss in my 2cents. For safety's sake, if it's broke, turn it off! The biggest problem is that as soon as there's a restriction, (like holding a finger over it to stop it), the pressure will shoot up and can cut you or inject oil into your squishy stuff. A pinhole leak can be really nasty and act like a saw blade. I was told by an old aircraft mechanic to check for leaks like that by using a piece of paper instead of my hairy knuckles...

normde2001 · Jul 26, 2014

"A pinhole leak can be really nasty and act like a saw blade. I was told by an old aircraft mechanic to check for leaks like that by using a piece of paper instead of my hairy knuckles..."

That was my original question, but from what they are saying this is only true if the system is under a load.

bumpyrider · Jul 27, 2014

True, but keep in mind what Chris said, " There is little or no pressure on a unloaded hyd system until it gets a load or resistance".

An open or broken line is almost always just a big mess, but once in awhile it can get you in trouble.

Pressure and flow are related to each other. If there's no resistance (open hose), you'll get the maximum flow out of the pump, (maybe 6 gal/min?) with very little pressure. When you have a restriction or a load, the pump stills wants to push the 6gpm through the line, so it pushes harder and the pressure builds. With a good high pressure pump, you can go from almost nothing to thousands of pounds of pressure in seconds.

When you're working on a flowing line and it gets kinked or plugged, that's when the pressure spikes and the line can whip, or cut you. Even though we all do it, I was always taught to never tighten a leaking line under pressure, because the sudden pressure increase could pop the line off or break the fitting.

When the pump is off, or the valve's closed to that line, there's no flow or pressure, so nothing happens.

A garden hose works the same way, but the pressure's only around 100psi instead of around 2000psi. If you got one to waste, punch a tiny hole in it and then cover the end. Try it with the faucet on just a little, and then all the way on...(and on a hot day the kids will love it)

Sorry about getting wordy. Used to work in aerospace, and they'd totally hammer us on safety all the time. I guess some of it made it through the thick skull.