Hydraulic pressure question

bazman82 · Jul 22, 2019

So I got a pressure gauge hooked up and I am testing the pressure on my ports on the farmtrac 785dtc. It is rated for 2500psi in the manual. The gauge reads 2100psi at PTO speed and with the lever still holding the pressure drops. I did some adjusting with the valve and after dropping it to 1500 it stayed steady. So I adjusted up to 2000 and it drops. I now have it at 1800 steady but cant go higher before it drops.

Would I need a new spring or relief valve? Hoping it's something simple..

David88 · Jul 23, 2019

You take a quick connect, and neck it down with adapters or hose, to fit a pressure gage. 0-3000 gage. The attach it to the tractor connection and work the control lever and watch the pressure rise. Pressure sound be near 2000 psi. Use same lever you would use to lift implement.
I had farmtrac 330 hst and was similar problem.
I used a manual from reliable-store.com and it was very very helpful.. Someone told me it's technical but the manual had simpler ways for permanent fix

bazman82 · Jul 24, 2019

That's basically what I already did for the testing part. I just cant seem to get it to stay steady past 1800 psi. When I adjust the relief valve for it to go over 1800 psi it will for a second then immediately go back down even though I am holding the lever still.

bazman82 · Jul 24, 2019

Here is an example of what the pressure does. I was holding the lever at all times. The only time I let go was to let go and repull the lever and that's apparent when the pressure jumps up several times.

bazman82 · Jul 24, 2019

I took part of the relief valve out but couldn't get it all out. Not sure if I need a special tool to get the other half out. I took out what I could and everything looked good and clean then put it all back and ran several tests.

WranglerX · Jul 25, 2019

If you can not get pressure high enough to operate relief valve (2500 PSI) I suggest you might have a tired pump or some other problem in system.... Just a thought....

Dale

bazman82 · Jul 25, 2019

I am hoping it isn't the pump but the pump might actually be cheaper than some of the parts for the relief valve...I was looking at the workshop manual and it seems like it wouldn't be that hard to replace, just time consuming because having to take the left wheel and fender off to get to it.

If I adjust the valve to 1800 PSI then itll hold steady at that rating. If I try to go any higher by adjusting the valve, itll hit 2200 PSI but drop like it does in the video.

bazman82 · Jul 25, 2019

I am trying to see if there is another relief valve between the pump and the auxiliary hydraulics relief valve but I am not entirely sure what I would be looking for so I am just looking for the wording of relief valve or pressure relief..

mrmikey · Jul 26, 2019

To tell for sure if you need a pump, you should actually do a pressure/flow test. You could have all the pressure you'd ever need but with no flow you aren't doing a thing........Mike

bazman82 · Jul 26, 2019

mrmikey said:
To tell for sure if you need a pump, you should actually do a pressure/flow test. You could have all the pressure you'd ever need but with no flow you aren't doing a thing........Mike

I am fairly new with working with hydraulics as that I have never had this issue before so I am just trying to get things cleared up. I am assuming a flow test is different from a pressure test then?

The testing of the pressure that I did was at a rear port of the tractor. The lines that leave the rear distributor go to the 2 rear ports and to the loader from what I can see. So I figured testing it in a rear port would be no different than testing it at the loader control valve. Do I need to be testing it somewhere between the pump and the rear distributor?

mrmikey · Jul 26, 2019

I am assuming a flow test is different from a pressure test then?

Yes, you have the tester and dial up to the rated pressure and see what you get for flow. If the pump is shot for instance, you could have 10gpm for example at 0psi or no restriction, going into an open bucket for example. You run up the pressure in the tester by tightening up the pressure relief and the flow will drop due to internal leakage of the pump, how much it drops and the rating on the pump determines how good the pump is. Here's a random flow meter for exmple Hydracheck - Inline Flow Meter Test Kits - One Way Flow .........Mike

ericm979 · Jul 26, 2019

Usually the flow goes from the pump to the loader valve first. Then out the loader valve's power beyond port and to the accessory valves, and from them to the 3pt which is usually inside the transmission housing. With open center hydraulics the flow goes through each valve in series, never parallel.

If your loader valve has quick connects to the cylinders (to enable removing the loader) you could try testing at that point.

My understanding is that the loader valve's relief valve will trip if the pressure to the loader cylinders exceeds it's pop off value OR the pressure downstream exceeds it. I.e. the loader valve relief protects all the valves down stream from it. That means that if you have a relief at the loader valve and in the rear SCVs, and block the work ports on the SCV, then either or both reliefs would trip. That could result in what you're seeing.

Check if there is a relief pressure spec for the different valves. That's how is is on my Branson (per the shop manual) though the values are pretty close.

bazman82 · Jul 26, 2019

Ill have to follow the line from the pump then. It looked like it went to the rear valve first before going to the loader control valve but I can double check there. The loader relief valve, if it is the part of the valve that I am thinking, then it is already screwed all the way in which I assume would be max for pressure..

That flow meter sure is expensive. Does it work the same as a pressure test gauge as that I can just put a male QD fitting on the one end and plug it into a rear port?

ericm979 · Jul 26, 2019

You'd need to have an in and an out. Two connections. Keep in mind that hose runs, fittings, valves each reduce flow a little.

What problem are you trying to fix? Maybe there's an easier and cheaper way to diagnose it.

bazman82 · Jul 26, 2019

ericm979 said:
You'd need to have an in and an out. Two connections. Keep in mind that hose runs, fittings, valves each reduce flow a little.

What problem are you trying to fix? Maybe there's an easier and cheaper way to diagnose it.

It is a weak loader. It will lift round bales just fine with the rpms up alittle but I have a new grapple for the loader that weighs 1200lbs and it struggles. The lift capacity for the loader is 3800lbs so it shouldn't have an issue.

When I put together the pressure gauge and tested it out, I was only getting a 2000 PSI reading and once it hit 2000 it would drop even though I was still holding the lever. I made adjustments and it would hold steady at 1800psi but anything above that at it gives out. Now I was doing all the tests on a rear port since the relief valve that I saw was there.

It almost seems that something is releasing the pressure once it gets to about 1900 and I cant get it back unless I let go of the lever and start over again.

mrmikey · Jul 26, 2019

That flow meter sure is expensive. Does it work the same as a pressure test gauge as that I can just put a male QD fitting on the one end and plug it into a rear port?

Yup. Better off putting it in the pressure line directly off the pump first, that way you're removing any variables from the test and you're testing just the pump. If that works out fine then go to your different sections.

It almost seems that something is releasing the pressure once it gets to about 1900 and I cant get it back unless I let go of the lever and start over again

Wonder if the pressure reliefs relieving the pressure then hanging up and the spool won't return until there's no pressure, just a shot in the dark. There's only one pressure relief correct? you don't have a relief on each section of the valve (if it is a multiple section vale that is

).........Mike

WranglerX · Jul 26, 2019

Perhaps this will help....

Hydraulic Pressure Test Gauge, Use and Operation - YouTube

Diagnosing Low Pressure in a Hydraulic System - YouTube

Kubtoa BX237 normal hydraulic loader pressures - YouTube

Dale

bazman82 · Jul 28, 2019

So I haven't had much time to check into anything yet but I have been talking with a friend that used to work in the service area of a tractor dealership. He mentioned to check the pipe that feeds the pump from the transmission housing to see if there is a screen on it. Since I will need to drain the hydraulic oil, I am thinking I will replace it with a higher weight hyd/trans oil. Right now I just replaced the old stuff with the cheap stuff from tractor supply. The 29.99 5gal bucket VP racing Ultra J20A Plus. It looks like the heavier Traveller Premium may do better.

The reason I am thinking this is when i went to use the tractor today the loader seemed to be a bit better than before but as it warmed up it wasnt as strong as when I first started it today. Maybe a heavier oil will help alittle...The manual calls for 10w-30 or 20w-30 or UTTO/API GL4/SCFG OT-1891. Not sure what the stuff is after the 20w - 30 though.

bazman82 · Jul 30, 2019

I had some time last night to mess with the tractor and look it over more thoroughly. It seems that I either have a leak somewhere around the pump or a worn pump. It looks like there is hydraulic fluid on the pump but it doesn't leak when sitting. I am assuming when the PSI gets to high, while using the loader or rear ports, is when it leaks and that is why I lose the pressure after 1800PSI. Does this sound feasible?

I am going to try and tighten up the bolts on the pump and see if that helps. The tractor has less than 1000 hours on it even though it is a 2005. Maybe the bolts weren't completely tightened from the dealership and it has always had this issue? I did a google search on the pump and it seems to be a common hydraulic pump. The item number is 2.4539.620.0. pump 22.5 cc - Bosch is what it says on the parts manual. I tried finding a place to sell them online in the states so that I could find a price but no luck just yet. I did see that Massey uses this pump and of course Deutz and SAME use this pump as well.