L**40 rear hydaulic pressure

[kuboman]

Kubo,

A test that might give you a clue is:

Lower the FEL to the ground. Install your Gauge in the rear QD. Start raising the FEL and while the FEL is moving carefully bump the rear DCV to if either or both of the following happen:

1) Does the FEL Slow or stop moving when you bump the rear DCV?

2) Do see pressure on the rear QD?

If yes to either of these questions some thing is not plumbed or working like we think it is.

If the loader stops or stutters this would indicate youare blocking the flow either to or from the FEL valve.

If the pressure is again high in the rear QD's would be the same concern as previous answer. Some thing isn't plumbed correctly.

If NO to either one of the conditions above I would check theoretical pump flow by timing the FEL raise time. Measure actual cylinder stroke for a given period of time.

If you know bore sizes of cylinders we can calculate pump flow. Knowing measured pump flow should tell us if there is flow by-passing the FEL control valve.

I am attaching a fluid power formulae spread sheet for your reference. It has a formulae that can be transposed to back figure pump flow from cylinder speed and time.

hope this helps.

Roy

As I read the flow schematics of the loader valve there is flow to PB port with the loader in the lift position. The idea being that you can still raise 3pt/rear implement and the loader. I have tried your #1 and yes the 3pt raises with the loader and yes there is pressure at the aux.valve. A LOT of pressure. The pressure spiked to the point where the 3500# gauge pinned the needle at the 6 0'clock position. Scarry. If I raise loader to point of by-pass then I loose all oil to back end. Makes sense as all the oils is bypassed at that point.
I do not see how it is plumbed wrong. It may be designed wrong but the plumbing is correct. I believe it is an inadequate system. The rear remotes are an after thought.
If someone with a L40 has a gauge it would be interesting to know if there loader and rear remotes are the same pressure.

 

[kuboman]

If you have a different pressure at the rear than at the loader, you must have more than one relief. There must be more to the hydraulic circuit than what you are seeing in the manual.

If there is one no one can find it. I have 3 mechs working on this and they all say there is one relief. I wish they were wrong but if there is one it is not obvious.

 

[J_J]

What you have said is totally illogical. If the pump max pressure is xxxx, then the FEL valve relief would be set about 50 psi below that. Perhaps you can show pictures of the two pressures in question.

If anything, a valve, cyl, hyd motor downstream of the FEL would cause the pressure to rise above the FEL relief valve, it would be relieved.

You can't generate more pressure than the pump can provide.

Are you using the same gage on both circuits.

Most relief valves are set the same, but if you have to set one valve less than FEL relief because of component limitation, you can. However any valve downstream of that valve will operate the same as the lower pressure.

The only thing that I can think of to generate more pressure that the pump can develop, is when you have a large force on a mechanical lever action on the fluid in a cyl.

For instance if you ram your bucket into a pile of dirt, it is possible to generate a back pressure spike way over the normal operating pressure that could damage equipment.

Maybe if you have two pumps, one pump might be able to develop more pressure than the other.

When you operated the remote to get that pressure, were you maxing out a cyl?

If you read that high pressure at the remotes, was the FEL relief doing anything?

If the FEL valve is maxed out, do you have any flow or pressure at the remotes?

If the FEL relief is set and operating correctly, the high pressure at the back will never build up because the FEL relief will relieve and maintain that pressure until the load is removed.

During the moment you are maxing out the lift cyl on the FEL, all the pump flow is going to either the cyl or out the FEL relief.

Can you make a video of the test you are doing.

 

[oldnslo]

As I read the flow schematics of the loader valve there is flow to PB port with the loader in the lift position. The idea being that you can still raise 3pt/rear implement and the loader. I have tried your #1 and yes the 3pt raises with the loader and yes there is pressure at the aux.valve. A LOT of pressure. The pressure spiked to the point where the 3500# gauge pinned the needle at the 6 0'clock position. Scarry. If I raise loader to point of by-pass then I loose all oil to back end. Makes sense as all the oils is bypassed at that point.
I do not see how it is plumbed wrong. It may be designed wrong but the plumbing is correct. I believe it is an inadequate system. The rear remotes are an after thought.
If someone with a L40 has a gauge it would be interesting to know if there loader and rear remotes are the same pressure.

Kubo,

One final test to confirm plumbing. Install the gauge in your FEL QD. If you have a second gauge install it in the rear QD. Activate the function on the FEL and you should see the 2500 PSI. Now while holding that function active slowly start shifting the rear DCV while watching the gauge in the FEL circuit. Does the pressure start to rise or stay steady? If you have a gauge in the rear QD do both gauges rise at the same rate.

If YES pressure rises in the FEL circuit with the pressure rise in the rear QD, that tells us that the tank line is being pressurized and the plumbing is not correct.

If the FEL pressure does not rise it tells us you have two different circuits and the one for the rear remotes is not being protected by the FEL relief. Oil is going to take the path of least resistance so if you are raising the loader and building excessive pressure on the rear remotes they have to be two different circuits.

Question becomes now, where or how is the second circuit being created.

Would have to be some form of flow divider or second pump.

Roy

 

[J_J]

I don't think we have the complete story here.

If he can work both valves at the same time and get two different pressures, and one of the pressures is above the pump pressure, he has two different sources.

If he tries to do anything while the loader is lifting, using full lever movement, there would be no fluid past the FEL valve.

So, if he has flow while the loader is lifting, that remote has another source of fluid, and I don't think the power steering pump would help any, or the hydrostatic transmission. Just what is the max pressure on the hydrostatic transmission?

I sure would like to see a video of the set up, with kuboman operating the levers and gages.

I guess people that read the first post about the two different pressure on an open center hyd system, are saying what the heck, no way.

I sure hope he post back with the answer to his problem.

 

[kuboman]

My gauge is correct I have checked it. The plumbing is correct unless they bent the pipes wrong. The tractor (3pt/remotes) get their oil from the power beyond from the loader valve. It is set up so there is still flow to the PB with the loader activated. There is one pump and one relief and yes I get one reading at the loader and a higher reading at the rear remote. I am not BS'ing here. You can get two pressures if there is some oil that bypasses the relief. It is possible I have a checkvalve that maybe faulty or it is a poor design. Someone out there has a L40 and a gauge that can either confirm Kubota messes up or I have faulty equipment.

 

[oldnslo]

My gauge is correct I have checked it. The plumbing is correct unless they bent the pipes wrong. The tractor (3pt/remotes) get their oil from the power beyond from the loader valve. It is set up so there is still flow to the PB with the loader activated. There is one pump and one relief and yes I get one reading at the loader and a higher reading at the rear remote. I am not BS'ing here. You can get two pressures if there is some oil that bypasses the relief. It is possible I have a checkvalve that maybe faulty or it is a poor design. Someone out there has a L40 and a gauge that can either confirm Kubota messes up or I have faulty equipment.

Kubo,
can you please post a schematic. Don't doubt your word for a second but what you saying just is not logical.

From everything you are describing you are using return flow from the tank port of your FEL valve and this is then a series circuit where your relief in the FEL valve will only work with the FEL functions. Any function down stream of this valve will pressurize the tank port of this relief and make it useless.

Roy

 

[J_J]

Is this your path of the hyd fluid?

Pump to FEL, PB out to the remote, remote PB out to 3pt?

or

Pump to remote, PB out to FEL, PB out to 3pt?

 

[J_J]

Roy,

If he is using fluid from the return port to feed the input to the remote, he would only have remote valve operation when the loader was used.

If the loader/FEL levers were in neutral, he would have no flow to the remote. The PB from the FEL would be going elsewhere.

To see if the one pump is developing that high pressure, install a gage first thing after the pump.

Maybe this is just a test situation/question for us with no good answer available.

Sometimes the Navy electronics instructors would give us an impossible question/situation, just to make us work really hard trying to figure it out, and the only right answer was that it was not possible.

It taught to do some through trouble shooting, and to use all the skills af analysis.

Knowing how something is supposed to work. What is it doing now , and what is it not doing.

Using process of elimination, and starting from the front end or the back end, and all good trouble shooting principles

 

[SPYDERLK]

The GL40's are designed with the loader valve integral with the tractor and it contains the only relief to the tractor. There is a safety valve for the 3 pt but it has nothing to do with anything else. The relief is set per the manual which I have been through many times. No one can explain the higher pressure at the back remotes but I am betting that every Gl 40 will do the same.

This describes my 7520 hyd system exactly. ... But, the prv on my Prince loader valve sets the system pressure. No valved pressure anywhere in the system will exceed the loader valve PRV setting. Also, the 3ph lift is dead unless Im just feathering the loader.
larry