To adjust or not to adjust.

[JC-jetro]

Howdy all,

I'd like to bounce a question off you guys for some perspective. My 3 point on my Ford 1700 works well. I have replaced hyd fluid, overhauled hyd pump and replaced lift piston seal ring. I just bought an oil filled pressure gauge up to 3000 psi and went to my place to check things out. My 3 point hyd system pressure pop off should be around 2300 psi per manual, but in reality it started popping off right at 1500 psi. I have no reason that my new gauge is off by 700 psi. Anyhow, the heaviest implement I pick up is my tiller @ 780 lbs, my Carry all full of tree trunk might be a hair over 900 lbs and the lift can pick it up with ease. I don't know what force it takes to pull a 6" wood post , 4 foot buried out of the ground, and again 3 point picks it up easy using my boom. My question is , should I even attempt to change the pop off setting and why. I don't have to shim the relief pop off as I do have an adjustment nut that can vary stiffness of the spring and it is a simple 5 minute job.

I tend to think raising the pop off is not buying me anything as long as I don't have to lift anything heavier than what I have already done in the past. I think it is best to expose the seals to no more than I need operationally if I can help it. Any pinions?

By the way , something else was puzzling to me was the pressure approaching zero as the 3point arrived at the height I intended. I know the feed back arm returns the spool to normal position(100% bypass to the reservoir), which at that point I still have an implement up in the air which the weigh of it should cause pressure in the lift cylinder. Reading zero did not make sense to me although there is no further flow when the lift system reaches it's intended height. Has anybody notice something like that?


JC,

 

[Soundguy]

The place you are checking may be between the pump and the spool.. or before the check valve.. Load in the air is gonna rest against the check valve.. depending on the valving.. might not show up once control valve is turned off and flow is diverted.. since you only need to have pressure inthe lift cyl.

I'll admit right off that I'm not up on the hyds controls o fthe new jap models.. vs the older unloading valve setup ford used.. etc.

soundguy

 

[JC-jetro]

The place you are checking may be between the pump and the spool.. or before the check valve.. Load in the air is gonna rest against the check valve.. depending on the valving.. might not show up once control valve is turned off and flow is diverted.. since you only need to have pressure inthe lift cyl.

I'll admit right off that I'm not up on the hyds controls o fthe new jap models.. vs the older unloading valve setup ford used.. etc.

soundguy

Chris,

Where I'm checking is between the lift cylinder and the spool valve as they recommend it. It should register oil pressure when I have an implement hanging in the air. where I read the pressure is on the lift cylinder head and the spool valve with all the flow diverted to the reservoir at the intended height. Going back to the question i had earlier, is there any point at all to up the pop off setting if I can already pick up the things I need with the 3 point system?

JC,

 

[jinman]

JC, I would not adjust the pressure unless I needed it. Since it's a simple job, why bother? Also, I think I'd get that gage calibrated by a known pressure. You said it's doubtful the pressure was 700 psi off and I agree, but since it read zero with a load hanging on the 3PH, it has to be suspect. I don't think there is any reason you could not use air pressure to chedk it. If you have an air compressor that can produce 90-100 PSI, why not use that to check the gage for low pressure response?

 

[dynasim]

I wouldn't change it, knowing that it could be changed in a jiffy if you need it. I rarely run out of lift while I am doing sensible things.

Don't 3pt hitches have the equivelant of pilot operated check valves. An indication is the hitch doesn't drop when working the loader with the tractor off. I guess it depends on where the pressure is being tested, but if you are upstream of that valve, the pressure will be zero.

Chris

 

[Soundguy]

I wouldn't change it, knowing that it could be changed in a jiffy if you need it. I rarely run out of lift while I am doing sensible things.

Don't 3pt hitches have the equivelant of pilot operated check valves. An indication is the hitch doesn't drop when working the loader with the tractor off. I guess it depends on where the pressure is being tested, but if you are upstream of that valve, the pressure will be zero.

Chris

That was my question.. if he was checking it before the check valve/hyd cyl circuit.. he may well read -0- pressure.. however if he is checking it between them. then he should read whatever pressure the cyl is experiencing. Speaking in general terms here, as i havn't been into the jap compacts much.

Assuming he is checking there.. unscrewing the valve should produce a stream of oil and let the cyl exhaust and drop.

I think I'd try that under a controlled response and reduced weight.. and then get that gauge checked like Jinman said..

soundguy

 

[Jerry/MT]

Howdy all,

I'd like to bounce a question off you guys for some perspective. My 3 point on my Ford 1700 works well. I have replaced hyd fluid, overhauled hyd pump and replaced lift piston seal ring. I just bought an oil filled pressure gauge up to 3000 psi and went to my place to check things out. My 3 point hyd system pressure pop off should be around 2300 psi per manual, but in reality it started popping off right at 1500 psi. I have no reason that my new gauge is off by 700 psi. Anyhow, the heaviest implement I pick up is my tiller @ 780 lbs, my Carry all full of tree trunk might be a hair over 900 lbs and the lift can pick it up with ease. I don't know what force it takes to pull a 6" wood post , 4 foot buried out of the ground, and again 3 point picks it up easy using my boom. My question is , should I even attempt to change the pop off setting and why. I don't have to shim the relief pop off as I do have an adjustment nut that can vary stiffness of the spring and it is a simple 5 minute job.

I tend to think raising the pop off is not buying me anything as long as I don't have to lift anything heavier than what I have already done in the past. I think it is best to expose the seals to no more than I need operationally if I can help it. Any pinions?

By the way , something else was puzzling to me was the pressure approaching zero as the 3point arrived at the height I intended. I know the feed back arm returns the spool to normal position(100% bypass to the reservoir), which at that point I still have an implement up in the air which the weigh of it should cause pressure in the lift cylinder. Reading zero did not make sense to me although there is no further flow when the lift system reaches it's intended height. Has anybody notice something like that?


JC,

2300 -1500 is 800 psi and I doubt your gauge is 800 psi off. It's possible but not very probable to have a 27 % of full scale error at the mid-range on a gauge.

Are you following the factory shop manual proceedure for checking the relief valve pressure ? You usually have to essentially run the pump dead headed to check this or overload the hitch to make it relieve. How do you know the relief valve is opening at 1500 psi during your test? The fact that you measure zero( or reservior pressure) after the hitch reaches the desired height says you are not measuring the pressure in the lift cylinder but somewhere downstream of the control valve which has returned to the exhaust position after reaching your desired hitch height. I'm not trying to be critical but I'm not convinced that you know the relief valve has opened.

However, if you are getting everything done that you need to do why bother screwing around with adjusting it. This is especially true if if there is something wrong with your test procedure.

 

[JC-jetro]

Thanks all for all your inputs. Appreciate it.

I'll certainly check the Gage for calibration as jim suggested with air. I doubt if there is anything wrong with the gage. I do read the pressure where they recommend it that is between the lift piston head and the spool valve. If the lift stays up the oil is trapped between a port on the spool and the lift cylinder and I intercept the pressure right in the middle. On the lift head there is a check valve as the pic below show it. My relief will chatter and relives oil if I raise the 3 point beyond its maximum height. The pressure for the relief is 2300 psi per manual.

You see the oil pressure line from the spool entering the head. The middle hole normal fill to the lift piston with a needle valve that regulates the rate of 3 point drop. The second from the right is check valved flow (one way only) to the lift piston. Flow can on back to the spool from the first hole on the right. The last hole on the left is also check valved (with 3 shims and pretty stiff spring ) that squirts oil directly in the rear differential to avoid shock loading of the lift piston nylon. I read the pressure off the fitting provided on the right side of the lift piston head. A closed spool valve to the lift cylinder should trap the oil between and weigh of the implement should compress trapped liq somewhat.

I don't thing I'll mess with it as I still believe " not to take thing to their limit if I achieve my tasks without stressing components out".

JC,


ps. on picture two , you'll need to look at the mirror image. The bolt on the right side is on the left as it is shown on 3rd pic.

 

[Jerry/MT]

Thanks all for all your inputs. Appreciate it.

I'll certainly check the Gage for calibration as jim suggested with air. I doubt if there is anything wrong with the gage. I do read the pressure where they recommend it that is between the lift piston head and the spool valve. If the lift stays up the oil is trapped between a port on the spool and the lift cylinder and I intercept the pressure right in the middle. On the lift head there is a check valve as the pic below show it. My relief will chatter and relives oil if I raise the 3 point beyond its maximum height. The pressure for the relief is 2300 psi per manual.

You see the oil pressure line from the spool entering the head. The middle hole normal fill to the lift piston with a needle valve that regulates the rate of 3 point drop. The second from the right is check valved flow (one way only) to the lift piston. Flow can on back to the spool from the first hole on the right. The last hole on the left is also check valved (with 3 shims and pretty stiff spring ) that squirts oil directly in the rear differential to avoid shock loading of the lift piston nylon. I read the pressure off the fitting provided on the right side of the lift piston head. A closed spool valve to the lift cylinder should trap the oil between and weigh of the implement should compress trapped liq somewhat.

I don't thing I'll mess with it as I still believe " not to take thing to their limit if I achieve my tasks without stressing components out".

JC,


ps. on picture two , you'll need to look at the mirror image. The bolt on the right side is on the left as it is shown on 3rd pic.

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"?

 

[Soundguy]

I too thought there must be a check valve between his pressure gaugfe and the laod for it to read -0-.. etc.

I'm just not familair with those new ones to second guess it though..

soundguy