Backhoe boom struggles to go up, drops when feathering up

[dirtyb115]

In looking at the valve pictures you posted it looks like there might be a plug that is connected to the “P” port. It is on right side valve in photo showing two sections and the “P” stamp on the casting. You could use that port or tee the gauge into the P line. This will provide pressure reading for all the functions. Run one function to end of stroke get reading, next, etc.

Looking at the complete valve photo The 2nd and 5th function might have work port reliefs. These are the silver hex fitting above the hose connection. They might be set lower than system relief so don’t panic if they show a lower pressure.

Ok, i had to order some adapters but i was able to put a gauge where the plug was on the P port. Had tractor at about 1800 rpm. I ran each function to the end of stroke and each one would max out at about 1500 psi, but if i held it at the end of the stroke it would bleed down to about 1100 psi. With the backhoe fully extended and boom all the way down i would try to raise it and like before it would not go all the way up, and it would hover right around 1100 psi. If i stopped and waited a few seconds i could get it to come up another inch before it would do the same thing. So what kind of pressures should I be seeing? And should it bleed off like that when at the end of a stroke?
Thanks!

 

[oldnslo]

I do not know what the pressure should be but 1,500 PSI seems low. Pressure dropping down to 1,100 PSI does not sound correct either.

Can you move the gauge to the loader circuit to see what pressures are there?

 

[dirtyb115]

I do not know what the pressure should be but 1,500 PSI seems low. Pressure dropping down to 1,100 PSI does not sound correct either.

Can you move the gauge to the loader circuit to see what pressures are there?

Trying to figure out where to tap in for the loader circuit, any ideas from the pictures? I see two plugs, but the one on top is not accessible (the hole is not centered). The hose on the bottom looks like it goes back to where the rear remote is. There are also two hard lines.

 

[oldnslo]

I could not see any “potential” pressure port options either. As a option you could put it in one of the quick disconnects for the loader and then operate that function. That will provide a pretty good idea of the loader circuit pressure.

 

[dirtyb115]

I could not see any “potential” pressure port options either. As a option you could put it in one of the quick disconnects for the loader and then operate that function. That will provide a pretty good idea of the loader circuit pressure.

Had to order a few more fittings, but was able to test it just now. Acting very similar, I put the gauge on one of the loader quick disconnects and it will get up to about 1800psi, but if i hold it, it slow drops in pressure to around 900-1000psi . Any ideas?

 

[oldnslo]

When checking pressure are you pulling the lever quickly or slower so pressure doesn’t spike. Possible if pulling lever quick you could see a spike and then decay but suspect would decay pretty quickly. Dropping 800 PSI does not sound normal.

I suggest finding out what the pressure should be on that model tractor since 1,800 PSI seems low but I do not know what it should be.

Pressure - flow loss creates heat so I would start checking temperatures of components before and after you try to build pressure. When checking loader tank line should get warm from dumping over relief. If power beyond sleeve gets warm then you might have a bad O-ring on it allowing leakage. If pump housing gets hot then pump is potentially worn leaking internally.

 

[dirtyb115]

When checking pressure are you pulling the lever quickly or slower so pressure doesn’t spike. Possible if pulling lever quick you could see a spike and then decay but suspect would decay pretty quickly. Dropping 800 PSI does not sound normal.

I suggest finding out what the pressure should be on that model tractor since 1,800 PSI seems low but I do not know what it should be.

Pressure - flow loss creates heat so I would start checking temperatures of components before and after you try to build pressure. When checking loader tank line should get warm from dumping over relief. If power beyond sleeve gets warm then you might have a bad O-ring on it allowing leakage. If pump housing gets hot then pump is potentially worn leaking internally.

Long post sorry... So I am trying to figure out what the 3 positions do for the AUX. HYDRAULIC LEVER (See attached pictures). RK has not been very helpful in explaining what they do. So in the position furthest away from the seat I assume applies pressure to the backhoe (or whatever i have in the rear remotes.). In the middle position the 3 point hydraulics work. In the position closest to the seat I can not figure out what this does. I do notice when I put the lever in this position the hydraulics sound like they get loaded down even though I am not using anything. Is this normal? The loader functions in all 3 positions which i assume is normal since it is first in line.

To answer your first question,
I was quickly pulling the lever. I tried again going slowly. It would get to 1500 psi, and slowly drift down to 1000 psi, however this reading varies depending on the AUX lever i mentioned above. If i have the lever furthest away from the seat (backhoe operation) it would only get to about 550 psi, and hold steady.

I could not find any documentation in the tractor manual, but the loader manual says the relief valve setting should be 2347 PSI.

I am not sure how hot the gear pump casing should get, but after running for a while the one side of the pump was pretty hot...... too hot to keep my hand on it.

Forgive me, not sure i understand "If power beyond sleeve gets warm" ?

Thanks again, sorry for the long post.

 

[rScotty]

Hi all. I have a new to me RK37 with the backhoe option. I was using it the other day to dig a couple of holes for some new trees and it was barely able to get the boom all the way up especially if the other cylinders were extended. I had the rpms up around 2000. I also noticed that when i try to go up with the boom very slowly it actually drops. If i go faster, it drops a small amount before going up. Any ideas on things i could check/try?

I was also curious, should the stabilizers be capable of lifting the tractor off it's rear wheels?

Thanks!

Going back to your basic question about slow performance coupled with even slower performance when moving the controls slowly points begins to make some sense. Thanks for adding in the BH pressure/FEL pressure.... and then the heat information.

Given all that, I agree with several other previous contributors that the combination of the hydraulic pump & main relief valve is not putting out enough pressure. These compact tractor hydraulic systems are all similar, and are designed to operate at about 2500/2850 psi. That limit is because the safe continuous operating pressure of the most common class of hydraulic fittings is just a little over 3000 psi and you want to stay below that.

The main relief valve is located hydraulically right after the outlet of the pump, of course. Mechanically, it is usually incorporated into the FEL control valve. The relief pressure is designed to be adjustable either by way of a screw compressing a spring or by shims. Since you have a gauge, you are ahead of the game. I would increase relief valve setting a little at a time and see if you can bring the system pressure up to somewhere in the 2000 to 2500 psi range. If you can, then see what that gives you in BH power. If you cannot achieve that much pressure, then suspicion falls on a worn hydraulic pump, or a defect in the internal drillings of the FEL control valve.
good luck,
rScotty
Oh, and to your original question. A backhoe can easily lift the back of the tractor off the ground - or at least I've never seen one that could not.

 

[dirtyb115]

Going back to your basic question about slow performance coupled with even slower performance when moving the controls slowly points begins to make some sense. Thanks for adding in the BH pressure/FEL pressure.... and then the heat information.

Given all that, I agree with several other previous contributors that the combination of the hydraulic pump & main relief valve is not putting out enough pressure. These compact tractor hydraulic systems are all similar, and are designed to operate at about 2500/2850 psi. That limit is because the safe continuous operating pressure of the most common class of hydraulic fittings is just a little over 3000 psi and you want to stay below that.

The main relief valve is located hydraulically right after the outlet of the pump, of course. Mechanically, it is usually incorporated into the FEL control valve. The relief pressure is designed to be adjustable either by way of a screw compressing a spring or by shims. Since you have a gauge, you are ahead of the game. I would increase relief valve setting a little at a time and see if you can bring the system pressure up to somewhere in the 2000 to 2500 psi range. If you can, then see what that gives you in BH power. If you cannot achieve that much pressure, then suspicion falls on a worn hydraulic pump, or a defect in the internal drillings of the FEL control valve.
good luck,
rScotty
Oh, and to your original question. A backhoe can easily lift the back of the tractor off the ground - or at least I've never seen one that could not.

I am guessing its on this block. Part 12-02 right before the loader valve. Sure is not going to be easy to get to if that is it. It looks like its on the back side so i will have to unbolt it to get to it.

https://www.rktractors.com/pdf/parts/RK37S.pdf

pages 150,151

I guess thats the PTO valve assembly.
There is another relief valve on pages 146,147, any change that would be the main relief?

 

[oldnslo]

Dirty B
It is hard to tell if that relief on page 146 is for the 3 point or a main system relief. Can you follow the pressure line from the pump to see what it is connected to? First item connected should have the relief valve in it.