hydraulics

davidseaquist · May 18, 2007

I don't understand hydraulics well, I have a skid steer type tractor with hydraulics to run the pto. My tractor is an Ingersoll Rand BL370. I was told by Ingersoll that my auxsillary hydraulics are set to 3,500 psi and adjustable up to 4,500 psi and the flow is standard flow 13.5 gpm. Does horse power available to hydraulics have anything to do with pressure ? I would like to run a hydraulic motor with a pto shaft they are available at Surplus Center. I would like to hook up a chinese chipper to it. What would happen if I stopped the flow to the chipper, would it wind down slowly? or try and stop right away? I looked at a three point hydraulic pto system at skid steer solutions and they say you need an overrun clutch ? They cost about 1,800 dollars. I was told I could get about 25 pto hp from a hydraulic motor. Why does pressure vary with tractor hydraulic systems. Thanks David

Farmerford · May 18, 2007

David:

Precise formulae are available, but a convenient rule of thumb is 1gpm @ 3,000psi = 2hp, and each factor is linear. So increasing the pressure 50% to 4,500psi increases the hp by 50% also. Using round numbers, 13 gpm@ 3,000psi=26hp, so 13 gpm @ 4,500psi = 39hp. Assuming system losses (friction, pumping, leakage, filters, etc) of 25% (which is high), you would still have 30hp+ at the PTO shaft.

The system should allow the tool (chipper) to turn faster than the motor to avoid damage if the fluid flow is stopped suddenly when the tool is rotating rapidly. The mechanical solution is an overrunning clutch between the hydraulic motor and the tool. The hydraulic solution is a check valve across the motor ports that allows fluid to flow only from the motor output (low pressure port) to the motor input (high pressure port). The valve is closed during normal operation, but if the fluid flow stops suddenly (and if due to the valving in the loader it cannot circulate freely through the system), the fluid in the motor will just circulate through the check valve, back into the motor, back into the check valve, etc., until the motor winds down.

I don't know about your chipper, but I have a 6" Vermeer PTO chipper. My Kubota L2900 with 29 PTO hp is barely able to drive it and it is easily stalled if the feed system is set too fast. It works for me because I am still slower getting limbs to it than it is chipping them up, but if several people are feeding it there are waits.

MossRoad · May 18, 2007

What kind of implements can you run off of your hydraulic PTO now?

Can you run a mower that has a hydraulic motor?

If so, you probably have a motor spool valve in your hydraulic PTO circuit. This allows a motor to continue turning once you shut off flow to it. That allows the motor to "coast" or spin down on its own, rather than abrupt stop if you halt the flow of hydraulic fluid.

That takes care of your shutting down nicely needs. Now on to your "I jammed the chipper with large piece of wood" scenario....

Let's say you toss in a really big, hard, knotty piece of somthing with a steel angle iron in it for good measure. This would cause the chipper to slam to a stop. You hydraulic PTO should have relief valves in it so that if the pressure exceeds the setting on the relief valve, it bypasses the fluid back to the tank.

Ask Ingersoll about that and see if what I told you is correct, just to be sure.

davidseaquist · May 19, 2007

MossRoad said:
What kind of implements can you run

off of your hydraulic PTO now?

Can you run a mower that has a hydraulic motor?

If so, you probably have a motor spool valve in your hydraulic PTO circuit. This allows a motor to continue turning once you shut off flow to it. That allows the motor to "coast" or spin down on its own, rather than abrupt stop if you halt the flow of hydraulic fluid.

That takes care of your shutting down nicely needs. Now on to your "I jammed the chipper with large piece of wood" scenario....

Let's say you toss in a really big, hard, knotty piece of somthing with a steel angle iron in it for good measure. This would cause the chipper to slam to a stop. You hydraulic PTO should have relief valves in it so that if the pressure exceeds the setting on the relief valve, it bypasses the fluid back to the tank.

Ask Ingersoll about that and see if what I told you is correct, just to be sure.

I do have a hydraulic Post hole digger with a hydraulic motor that I have run off of the backhoe, it was made to be run off of the loader circit. Would the loader auxillary circit, and the backhoe auxillary circut run the same.
[ have the motor spool valve ? ] David

davidseaquist · May 19, 2007

So far I have run a hydraulic splitter/ root grapple rake/ and grubbing bucket with thumb. Off of the loater auxillary hydraulics. I will ask Ingersoll Rand if I can run a hydraulic motor with out running an overrun clutch. I have not run the post hole digger off of the loader. I wonder what speed the post hole digger motor runs ?

davidseaquist · May 20, 2007

I found a sight for Hydraulics & Pneumatics. It seems to be for professionals and engineers. The sight is called
[ Url:Hydraulics Pneumatics: Welcome ] I found atricles in the archives of hydraulic motors and speed control of hydraulic motors.
I seem to be having a problem locatine a hydraulic motor that runs at about 540 rpm high torque low speed that handles pressures to 3,500 psi orerating pressure to 4,500 psi initial pressure. David

Farmerford · May 20, 2007

Look at the Char-Lynn Series 2000 motors at Surplus Center. You probably need a 4.5 to 5.0 cu in/rev one. Surplus Center also has a 1 3/8" 6 spline male shaft adapter to convert them to PTO drivers.

If your auxiliary hydraulics properly operated a grapple then you probably do not have a motor spool in the directional control valve. If you had a motor spool valve, the grapple would not have remained open or closed because in a motor spool valve the work ports are connected to tank when the spool is in neutral. That's what lets the motor freewheel as MossRoad explained.

PTO overunning clutches are available for less than $100 or you can use the check valve across the motor ports I mentioned earlier. I used a check valve because I coupled the motor directly to the gearbox and needed to keep it close for space limitations, and because all the aftermarket overrunning clutches I am familar with have a single pawl (that's why they are so cheap) and I don't like the bang you get when starting the PTO (although it doesn't seem to hurt anything).

SPYDERLK · May 20, 2007

As Farmerford said, a check valve is a good Hmotor protector, but yould have to get clever to allow a reverse option. A motor spool valve gives you protection, and reverse included at a cheaper cost and greater convenience and reliability than an o/r clutch.
larry

davidseaquist · May 21, 2007

I found this motor on E-bay What do you think.
Item number 250117949281 David

Farmerford · May 21, 2007

You should check the Eaton/Char-Lynn catalog for specifications, but I think that is an 8.0 cu in motor that turns 576 rpm @ 20 gpm. Your 13.5 gpm will drive it about 390 rpm which is too far below the required 540 rpm to be satisfactory. You need either the 6.2 cu in model to give 500 rpm at 13.5 gpm or the 4.9 cu in model to give 612 rpm. I would probably select the 4.9 cu in and slow the engine about 10% from the speed at which it produces 13.5 gpm. That should produce about 12 gpm and 545 rpm.

It does appear to have the check valve across the motor ports I mentioned and the hoses, flat face couplings, and motor coupling are worth $100 or so if you can use them.

But beware Char-Lynn 1 1/4" keyed shaft motors: some of them use a 5/16" keyway which is an acceptable choice under SAE standards, but most everyone else uses a 1/4" keyway, so couplers, shafts, and adapters with a 5/16" keyway are hard to find. I note that the seller includes a coupler.