To adjust or not to adjust.

[JC-jetro]

These pictures show two relief valves; one downstream of the pump and one in the lift cylinder head. the one at the head of the cylinder is probably for shock loads from implements to the cylinder head it self. The other one is the system relief. Which do you think you have a problem with?

I think the 2300 psi one is the the system relief. It vents the pump to the reservior if the if you overload the lift, for example. The other relief is a dynamic relief valve that relieves the lift cylinder head from short term transient shocks (pressure spikes) from the implements during transport. This typically the way the 10 series Fords are designed. the relief system tests for the 10 Series uses some special equipment that allow pump flow to pass and then you throttle down the pump flow til the system relief valve opens.

It's not checked with a simple pressure gauge.

The other relief valve is set for high pressure and dynamic loading ( for instance during travel over a rough fielswith an implement raised ) so it's not going to go off at steady state conditions.

I'm certainly no expert on these systems but the fact that you are not having any trouble with failure to lift tells me you system relief is not the problem. The place where you are measuring the pressure is just showing you that for what ever load you have on the hitch, that's the pressure required to get the load to that position. I believe you said that was 1500 psi. The pressure drops because the control valve attempts to hold that position via the check valve ( 2 in the left picture) in the cylinder head. That's why your pressure goes to zero. The cylinder check valve is holding the lift up. If you have some leakage and the lift starts to drop, the control valve will add fluid until the commanded position is again reached and then the cylinder check valve will hold the load.
How do you get the hitch to go above it's maximum height to get "the valve to chatter"?

Thanks for your input. The things you mentioned about your two beginning paragraphs were known to me as my earlier post indicates and I came up with the same understanding of the system as you have. As I have shown in the pic and explained corroborated with the diagrams the two check valves have separate function. with one as shock relief and second on as normal passage to the lift piston housing. On earlier pictures I showed 3 holes on the piston head. There are two normal passage way for the flow to get to the piston one thru the needel valve if it is not closed and secong thru the light spring and the big ball check valve. reason for it is to be able to raise the implement even if the rate of drop needle valve is closed. rate of drop needle valve is the only way you can return flow to drop the 3 point, second hole check valve allows flow only towarf the piston and not the other way around.

I do not have any issue with my 3 point as I can lift anything I need with teh 1500 psi setting as it is right now. As jim and several others shared my opinion that ; i dont't need to mess with it" unless there is a need.

Again , reading zero is some what of suspect as even with the pump and engine off I still have trapped oil between spool and the lift piston. The weigh of lift arm only and more so with an implement in the air will
force the rock shaft to turn hence pushing the piston against the trapped oil causing some pressure. I expect to see pressure then even if tractor is off. It's just like balloon that has trapped air, even with no flow you should be able to read pressure. I don't believe the statement you made below is not valid for my scenario.

The pressure drops because the control valve attempts to hold that position via the check valve ( 2 in the left picture) in the cylinder head. That's why your pressure goes to zero.

Chris,

In my situation it does not matter if I read the pressure on either side of the check valve as long as rate of drop needle valve is open. The pressure gage connection is again upstream of the check valve and right in the middle point where oil is trapped between the cylinder and spool valve.


JC,

 

[Soundguy]

Then you really should be reading pressure on the gauge.. if it is between the check valve and the piston.. it's a puzzler why you are not...If you unscrew the gauge, will oil exhaust and the lift drop? If so.. then i'd say the gauge is very defective..

soundguy

 

[Jerry/MT]

Thanks for your input. The things you mentioned about your two beginning paragraphs were known to me as my earlier post indicates and I came up with the same understanding of the system as you have. As I have shown in the pic and explained corroborated with the diagrams the two check valves have separate function. with one as shock relief and second on as normal passage to the lift piston housing. On earlier pictures I showed 3 holes on the piston head. There are two normal passage way for the flow to get to the piston one thru the needel valve if it is not closed and secong thru the light spring and the big ball check valve. reason for it is to be able to raise the implement even if the rate of drop needle valve is closed. rate of drop needle valve is the only way you can return flow to drop the 3 point, second hole check valve allows flow only towarf the piston and not the other way around.

I do not have any issue with my 3 point as I can lift anything I need with teh 1500 psi setting as it is right now. As jim and several others shared my opinion that ; i dont't need to mess with it" unless there is a need.

Again , reading zero is some what of suspect as even with the pump and engine off I still have trapped oil between spool and the lift piston. The weigh of lift arm only and more so with an implement in the air will
force the rock shaft to turn hence pushing the piston against the trapped oil causing some pressure. I expect to see pressure then even if tractor is off. It's just like balloon that has trapped air, even with no flow you should be able to read pressure. I don't believe the statement you made below is not valid for my scenario.

The pressure drops because the control valve attempts to hold that position via the check valve ( 2 in the left picture) in the cylinder head. That's why your pressure goes to zero.

Chris,

In my situation it does not matter if I read the pressure on either side of the check valve as long as rate of drop needle valve is open. The pressure gage connection is again upstream of the check valve and right in the middle point where oil is trapped between the cylinder and spool valve.


JC,

The reason you read zero is because the check valve at the lift cylinder head is closed and the pump pressure is dropped to reservior pressure threough the control valve. The thing holding your lift up is the checked pressure in the lift cylinder. That's the only explanation I have for the zero gauge reading once the lift stops moving. I don't for a minute think it is a defective gauge.
The thing that isn't shown in your diagram is how the cylinder exhausts for a drop. There has to be another passage on the lift cylinder head leading through the contol valve to allow that to cause the cylinder to drop on command. I believe their is a dual passage leading to the control valve and the needle valve only retricts part of the flow since if the flow contol needle was fully closed and it was the only exhaust, you could not drop the lift. So there has to be another passage and it's not shown on your diagrams..

 

[Hooked_on_HP]

JC
You have to raise your controll lever past the stop to get the cylinder to fully extend and build up enough pressure to check the bypass. In your service manual look at the adjustment for the position control link and it explains how to check the bypass.
Bill

 

[JC-jetro]

Then you really should be reading pressure on the gauge.. if it is between the check valve and the piston.. it's a puzzler why you are not...If you unscrew the gauge, will oil exhaust and the lift drop? If so.. then i'd say the gauge is very defective..

soundguy

Soundguy,

It is indeed a puzzler as I have my gauge between piston and the spool valve. If I have a an implement up in the air without any doubt I have oil trapped between the piston and the spool valve, that's exactly what it hold the implement up. Please look at the diagram below with directional arrows, the only highly unlikely scenario is that I have my rate of drop knob completely in closed position, if then I lowered the implement, the pressure is relived to diffy without the lift dropping but I have not done that though. What I have not shared with you all is that is the second gage I got, the first one could not read anything at all and the second one was sent to me after I called Northern. can hardly see that I got two lemons in row, although have to admit "Murphy" and I go way back

This is at all not a concern but it is only my curiosity, I'll get to it when I get a chance and will report.

 

[Soundguy]

I understand what you are saying.. but do this quick go/no go test..

get something lifted in the air.. put your gauge on.. AFAIK.. you are saying it will read -0-.. use a wrench and slowly unscrew that gauge that you believe is betweent he piston and spool valve.. with no check valve between the gauge and piston. If you are correct, oil will start seeping as the gauge becomes loose, and then when you pull the gauge. the ?8oz? of oil inthe cyl will immediatly exhaust out the gauge hole and the lift will drop.

If however.. you unscrew it and there is no pressure there.. then there must be a check valve ahead of it like I and Jerry are thinking.

Not saying you are wrong.. just tryin' to figure it out. guess it could still be a 2nd lemon gauge.. but that's unlikely.

bottom line.. lift is stying inthe air with weight on it.. and that will be pressure if the gauge is on a line with no check between the gauge and the cyl..

post back

soundguy

 

[Soundguy]

In looking at the diagram.. 2 feeds the cyl thru a check.. If that manual flow valve is tightened.. you wouldn't see pressure at the gauge.. however.. if it is open, and there is no check on that port where the oil can come out o fthe piston.. then the exhaust line leaving must see a closed valve .. or a piloted check in that line.. or the lift would never pressurize...

makes me want to think there's a unlisted check somewhere!.( like right before the gauge.. but after the port to 4/5 closed side of the spool..like right where your #6 blue dot is is where i would expect it to be with what we are seeing / hearing ) . can't figure which is more likely.. 2nd bad gauge.. or unlisted check.. if you pull the gauge can you look down the manifold and see the manual flow shutoff valve neddle / seat?

ya got to get to the bottom of this and tell us!

soundguy

 

[JC-jetro]

The reason you read zero is because the check valve at the lift cylinder head is closed and the pump pressure is dropped to reservior pressure threough the control valve. The thing holding your lift up is the checked pressure in the lift cylinder. That's the only explanation I have for the zero gauge reading once the lift stops moving. I don't for a minute think it is a defective gauge.

The thing that isn't shown in your diagram is how the cylinder exhausts for a drop. There has to be another passage on the lift cylinder head leading through the contol valve to allow that to cause the cylinder to drop on command. I believe their is a dual passage leading to the control valve and the needle valve only retricts part of the flow since if the flow contol needle was fully closed and it was the only exhaust, you could not drop the lift. So there has to be another passage and it's not shown on your diagrams..

I respectfully disagree with your statement in the first paragraph. In an open center when the spool is moved to neutral position flow in one port is directed to the reservoir but a different port is plugged same as a 3 way valve diverting valve.

I have shown in previous diagrams and explained exactly how the cylinder exhaust for a drop. It is done thru the spool valve. several post ago I have shown plumbing for the cylinder head and also control spool valve. Please also refer to the diagram in my response to Soundguy's post that has flow directional arrow. I do agrees that if rate of drop needle valve is fully closed, lowering the lift arm can relive the pressure to zero but in that case lowering the arm can not not lower the 3 point as check valve allows flow only from spool to lift piston and not the opposite way. the thing is the needle was was never closed as I was able to easily lower and raise the 3 point repeatedly.

So far whatever was shown on my diagrams were exactly as I found out by taking the system apart, and have no reason to believe my diagrams are incorrect.

Thanks,
JC,

 

[Soundguy]

I think we are getting closer and narrowing it to a couple equally unlikely possibilities...If the diagrams aren't incorrect.. then when you unscrew the gauge reading -0- witht he lift up.. and under a test load.. nothing too big.., then a few oz of oil should shoot out the gauge port and the lift should drop.. if it dont drop... the books wrong... if it does drop.. gauge is bad...

soundguy

 

[JC-jetro]

JC
You have to raise your controll lever past the stop to get the cylinder to fully extend and build up enough pressure to check the bypass. In your service manual look at the adjustment for the position control link and it explains how to check the bypass.
Bill

That's true Bill, I have raised it passed the stop to cause the relife to chatter and open up. That is also how it is recommended in the manual.


JC,