L**40 rear hydaulic pressure

[kuboman]

If the rear remote circuit back-feeds pressure to the loader valve and the loader valve was leaking in the up direction, the larger surface on the piston side of the boom cylinders will create enough force to overcome the smaller piston surface on the rod side of the cylinders, meaning the loader will raise.

Feathering valves does funny things sometimes, I don't fully understand the valve geometry and the PB part of the circuit, I just know that it works, better in some cases than others obviously.

Did you happen to check the pressure at a higher engine speed, or still at idle?

Sean

I did check pressures at higher engine speed and it did not vary more than 50psi so it is obviously relief pressure.

 

[kuboman]

Kubo,
Sorry, never even gave that a thought but yes the loader would lift some do to the spool configuration. What happened is that when you moving the loader valve to the lower position it also opens the cap end of the lift cylinders to the down stream PB which feeds the RR. Loader should only lift until both sides of the cylinders see pressure.

Did you get pressure readings or do the intelligent thing and go what the heck and stop?

This at least confirms again that the valves are plumbed correctly, but do to me not thinking it completely through caused you a little panic.

Would you be willing to try it again only possibly disconnect both lift hoses or use the curl. That spool does not feed flow down steam to the PB port. Would sure like to see if both pressures are the same with the RR dead headed.

If they are the same this will really scramble my pee brain.:confused2::confused2:

Sorry again

Roy

I did keep track of both pressures and they appeared to stay the same. I lifted the loader about 4' before stopping. Retried again with same results. Did not scare me just surprised. But now that someone explains it it does make sense.
I will try your experiment with the curl circuit and report back.

 

[kuboman]

OK curl test results.
I pressured the curl circuit to about 700# and then pressured the RR.
The RR went up to 3000+ as I continued to pressure up the curl the RR went down to about the point where they both were at the same pressure which was about 2500# at that point the relief was wide open and I lost all pressure to the rear remote.
Hope this makes sense.

 

[oldnslo]

But now that someone explains it it does make sense.

Finally something makes sense... :thumbsup:

 

[Leejohn]

I have been reading what everyone is saying and trying to put 2 and 2 together.
What I keep coming back to is the loader valve. I would say there is 3000psi at the valve when checking the rear remotes. So that tells me the valve body is not open to the loader relief valve, but it is open to spools 1 and 2. When checking the spools you get your 2000+psi and the remotes drop in psi and then let up on spool check the pis goes back up.
So I guess the bottom line is, have the dealer change the loader valve or pull the relief valve and see if it open to the pump port.

 

[oldnslo]

OK curl test results.
I pressured the curl circuit to about 700# and then pressured the RR.
The RR went up to 3000+ as I continued to pressure up the curl the RR went down to about the point where they both were at the same pressure which was about 2500# at that point the relief was wide open and I lost all pressure to the rear remote.
Hope this makes sense.

Did both gauges show 3000+?

 

[J_J]

Roy,

What is the purpose of dumping fluid from a loader cyl back into the PB? Does it have anything to do with regen, and then if he deadheaded the remote, would the regen pressure from the cyl add to the pump pressure.

If the valve has regen, how does that affect anything downstream.


Kuboman,

I am not sure where you are placing the gages, but if the gage were placed in the IN port of the loader valve, you would see the pressure results from any valve you operate.

If you were to only use 5 GPM out of 10 GPM from the pump to operate the FEL, just lifting the FEL would only be a couple of hundred of lbs, and when the cyl were fully extended, the relief would activate and relieve at 2550 psi, and this relieved fluid would go to the OUT port. You will still have 2550 psi as long you held the valve lever in extended position.

The question, still is, how is a gage down stream, reading a higher pressure. The mystery
is still among us.

At the same time as the FEL is relieving, you are still holding pressure on the FEL at 2500 psi, and you also have the 5 GPM flowing through the system through the remote and the 3pt, and should be able to operate either valve. If you do operate any other valve , what should the gage read? Deadhead pressure , load pressure. You are already showing FEL relief pressure, using the 5 GPM flow, and that is being relieved.

If you only have the one gage installed at the IN port of the FEL, and you raise the 3pt until the relief goes off, you should see the 3pt relieved pressure on the gage.

If the first valve up stream uses all the 10 GPM flow, there should be no flow and pressure to the second and remaining valves, if the relief can handle the relieved volume of fluid, which would be 10 GPM.

All three valve could use some of the fluid for their circuits at the same time, and if the last valve only goes into relief, the total flow path is pressurized, but should only show the relief pressure, or operating pressure.

 

[kuboman]

Did both gauges show 3000+?

No just RR.

 

[oldnslo]

Roy,

What is the purpose of dumping fluid from a loader cyl back into the PB? Does it have anything to do with regen, and then if he deadheaded the remote, would the regen pressure from the cyl add to the pump pressure.

If the valve has regen, how does that affect anything downstream.

Purpose of the raise lower spool dumping oil into the PB port is so that you can raise at full speed and still operate the bucket. Only regen spool is on the bucket dump and it does not feed oil into the PB.

Kuboman,

I am not sure where you are placing the gages, but if the gage were placed in the IN port of the loader valve, you would see the pressure results from any valve you operate.

If you were to only use 5 GPM out of 10 GPM from the pump to operate the FEL, just lifting the FEL would only be a couple of hundred of lbs, and when the cyl were fully extended, the relief would activate and relieve at 2550 psi, and this relieved fluid would go to the OUT port. You will still have 2550 psi as long you held the valve lever in extended position.

J_J
If you feathering the lift to only use 5 GPM out of 10 at 500 PSI even when the cylinders stop moving you will not force oil the relief. Since you are feathering or metering the oil to the lift circuit. When that flow requirement stops the oil will take the path of least resistance which would most likely be through the metering on the PB and then flow on downstream. granted the pressure will probably increase to 1000 PSI or more but would still be less than the RV setting.

The question, still is, how is a gage down stream, reading a higher pressure. The mystery is still among us.

At the same time as the FEL is relieving, you are still holding pressure on the FEL at 2500 psi, and you also have the 5 GPM flowing through the system through the remote and the 3pt, and should be able to operate either valve. If you do operate any other valve , what should the gage read? Deadhead pressure , load pressure. You are already showing FEL relief pressure, using the 5 GPM flow, and that is being relieved.

If you only have the one gage installed at the IN port of the FEL, and you raise the 3pt until the relief goes off, you should see the 3pt relieved pressure on the gage.

If the first valve up stream uses all the 10 GPM flow, there should be no flow and pressure to the second and remaining valves, if the relief can handle the relieved volume of fluid, which would be 10 GPM.

All three valve could use some of the fluid for their circuits at the same time, and if the last valve only goes into relief, the total flow path is pressurized, but should only show the relief pressure, or operating pressure.

J_J
Agree that the RV should relieve at the same pressure regardless of which function is being used. By having Kuboman gently feather the curl function which would now open this gauge to system pressure, and then operate the rear valve should simulate having a gauge teed into the pressure port. I.e. Both gauges should show the same pressure until the curl valve is shifted to block flow to the RR at which time the pressure at the RR Should drop to 0 PSI. Kuboman already stated there are no gauge ports on his tractor and does not have the equipment necessary to try and remove steel lines to install a gauge.

 

[oldnslo]

No just RR.

Did the pressure in curl appear to be similar as the pressure on the RR at pressures between 1000 & 2500 or was one always higher than the other?