Hydraulic pressure adjustment

[Bonaro]

I have an old L275 that I am bringing back to life.
The FEL seems to have enough lift power, I think the load capacity is about 1000 pounds and I have lifted 15 bags of concrete with no problem. However, not so much down power. It wont lift the front wheels off the ground.
I am in the process of making a pressure gauge with quick release fittings that I can put in-line and measure the pressure wile operating.
What is the process for adjusting the operating pressure of the hyd system?

 

[North Idaho Wolfman]

You don't have a pressure issue, if you did it wouldn't lift that kind of weight.
Your issue is either a design issue, several loader designs will not lift the tractor off the ground with the lift cylinders.
It could also be that the seals on the cylinders are in need of replacement, this is quite common on older loaders.

Did you try to lift it with the roll function?

 

[Bonaro]

You don't have a pressure issue, if you did it wouldn't lift that kind of weight.
Your issue is either a design issue, several loader designs will not lift the tractor off the ground with the lift cylinders.
It could also be that the seals on the cylinders are in need of replacement, this is quite common on older loaders.

Did you try to lift it with the roll function?

I tried the roll function and it will almost do it...not quite off the ground.

Is replacing hydraulic seals something I can do or does it require special tools?

 

[North Idaho Wolfman]

I tried the roll function and it will almost do it...not quite off the ground.

Is replacing hydraulic seals something I can do or does it require special tools?

Yes you can, it's all normal tools, you might need to get a spanner wrench (if needed) or maybe a interior seal installer.
Some of the older cylinders are a real bear to get opened up, but easy when you do.

 

[Tx Jim]

When attempting to raise frt tires with FEL were rear brakes released? For frt tires to raise with the least effort rear tires must be free to rotate while attempting to raise frt tires.

 

[Bonaro]

When attempting to raise frt tires with FEL were rear brakes released? For frt tires to raise with the least effort rear tires must be free to rotate while attempting to raise frt tires.

Yes, brakes were released.

I am going to do a pressure test to see what the pump is putting out. If good I will try adjusting the relief valve on the spool...it may be just the way it is. I dont want to dump a lot of money in it because it works well enough now.

I pulled the spool apart and got it all cleaned up. Tolerances are good but one of the control valves has a bit of mild pitting on it. I put it the lathe and polished it but it still has a enough pitting that I think it will weep fluid. These are stupid expensive.
Should I just run it and live with a little leak or it is possible to repair the pits with something like JB Weld and polish it down in the lathe?

 

[Henro]

Yes, brakes were released.

I am going to do a pressure test to see what the pump is putting out. If good I will try adjusting the relief valve on the spool...it may be just the way it is. I dont want to dump a lot of money in it because it works well enough now.

I pulled the spool apart and got it all cleaned up. Tolerances are good but one of the control valves has a bit of mild pitting on it. I put it the lathe and polished it but it still has a enough pitting that I think it will weep fluid. These are stupid expensive.
Should I just run it and live with a little leak or it is possible to repair the pits with something like JB Weld and polish it down in the lathe?

I do not think I would try to use anything that might break free and get into the hydraulic system if your tractor is HST. (sorry don't remember as I type this).

Even teflon tape is a no no for fitting on the hydraulic connections on a HST tractor, as a small piece could cause damage to the hydraulic pump(s). From what I have read anyway. This might also apply to non HST tractor hydraulic pumps.

 

[North Idaho Wolfman]

Yes, brakes were released.

I am going to do a pressure test to see what the pump is putting out. If good I will try adjusting the relief valve on the spool...it may be just the way it is. I dont want to dump a lot of money in it because it works well enough now.

I pulled the spool apart and got it all cleaned up. Tolerances are good but one of the control valves has a bit of mild pitting on it. I put it the lathe and polished it but it still has a enough pitting that I think it will weep fluid. These are stupid expensive.
Should I just run it and live with a little leak or it is possible to repair the pits with something like JB Weld and polish it down in the lathe?

First an foremost;
What you have done is wrong.
You can not remove any material from a spool valve, every 1000's matters.

The spool is matched with the housing, so you can't even buy a new spool to fit it, you will have to replace the entire valve assembly.

It was very unlikely the "leak was at the spool, it was very likely that the "leak" was and is still in the cylinder seals.

 

[Bonaro]

First an foremost;
What you have done is wrong.
You can not remove any material from a spool valve, every 1000's matters.

The spool is matched with the housing, so you can't even buy a new spool to fit it, you will have to replace the entire valve assembly.

It was very unlikely the "leak was at the spool, it was very likely that the "leak" was and is still in the cylinder seals.

Well...oil oozes out of the spool valve so thats where it is leaking and the spool part number is 70050-00743, available from Messicks for $843.

I know this is not why the loader has lowdown force, I was repairing a leak

 

[Bonaro]

The o-ring kit I ordered for almost $20 arrived after 18 days and it had the wrong o-rings.
I drove down to Industrial Hydraulics and bout the correct size for $2.36.
I got it all back together, not more leaks at all. Polishing the spools fixed the leak and it seems to work smoother now.
It still wont lift the front end off the ground but I can roll the bucket and lift it. After I build a pressure valve to see what the pump is doing I may try to adjust the relief valve but until next winter I got tractor stuff to do

 

[whitetiger]

Well...oil oozes out of the spool valve so thats where it is leaking and the spool part number is 70050-00743, available from Messicks for $843.

I know this is not why the loader has lowdown force, I was repairing a leak

That is the part number for the complete control valve assembly. You can not buy just the spool as they are select fit.

 

[whitetiger]

The o-ring kit I ordered for almost $20 arrived after 18 days and it had the wrong o-rings.
I drove down to Industrial Hydraulics and bout the correct size for $2.36.
I got it all back together, not more leaks at all. Polishing the spools fixed the leak and it seems to work smoother now.
It still wont lift the front end off the ground but I can roll the bucket and lift it. After I build a pressure valve to see what the pump is doing I may try to adjust the relief valve but until next winter I got tractor stuff to do

Polishing the shaft did not repair any leakage, the new seals repaired the external leakage.

 

[Dave_eng]

The radial clearance between the spool and bore in common, garden-variety directional control valves ranges between 3 and 13 microns.

10 microns is = 0.0004" Count the zero's after the decimal point!

Measuring these clearances requires instruments few outside the metrology field have.

fyi Metrology is “the science of measurement.

Dave

 

[lugbolt]

lifting the front end off the ground is not an indication of lifting power.

you have less surface area on the down side of the piston than you do on the up side, thus there IS GOING TO BE less downward force assuming the same pressure.

 

[Bonaro]

Polishing the shaft did not repair any leakage, the new seals repaired the external leakage.

Perhaps but the point is, it no longer bleeds oil. The o-rings certain helped a lot but the spools were dull when they came out and shiney when they went back in, which also helped

 

[Bonaro]

lifting the front end off the ground is not an indication of lifting power.

you have less surface area on the down side of the piston than you do on the up side, thus there IS GOING TO BE less downward force assuming the same pressure.

The piston travels in two directions inside the same bore. The force should be the same.
Please explain...
Are you referring to the amount of fluid displaced by the cylinder rod? Since the piston is the same diameter, the force should be the same, right?

 

[whitetiger]

The piston travels in two directions inside the same bore. The force should be the same.
Please explain...
Are you referring to the amount of fluid displaced by the cylinder rod? Since the piston is the same diameter, the force should be the same, right?

No, the force is NOT the same. The pressure is PER SQUARE INCH, you lose surface area from the shaft which is hydraulic logic 101.
If you have 1800 PSI on a 10 square inch surface and 1800 PSI on a 20 square inch surface, which one do you think has the most force or lift capacity? The bigger diameter of the cylinder, the more lift capacity you will get without raising the system pressure.

 

[ruger1980]

As whitetiger said there is less area on the rod side than on the barrel side so the effective force on cylinder extend vs retract will always be higher given the same pressure.

 

[Bonaro]

As whitetiger said there is less area on the rod side than on the barrel side so the effective force on cylinder extend vs retract will always be higher given the same pressure.

Ok, I see what you are talking about, Thanks

 

[Henro]

Well...oil oozes out of the spool valve so thats where it is leaking and the spool part number is 70050-00743, available from Messicks for $843.

I know this is not why the loader has lowdown force, I was repairing a leak

Are you sure that is not the price for the complete valve section (still high) or even for the loader valve assembly in its entirety?

Hard to imagine that would be the price for one piece of one of the valve sections. But what do I know?