Case DH4B Trencher/Backhoe Won't Spin Trenching Chain

[MTGreen]

Which relief valve, I do not know how to identify a/the relief valve

Every high pressure hydraulic circuit has a relief valve for over pressure built in and you may have more than one. If you trace the circuit from the tank to the pump to the valve to your hydraulic motor/cylinder and back to your tank, there will be a relief valve somewhere in the circuit that opens when the pressure gets too high to short circuit the fluid back to the tank and relieve the pressure. If that valve is stuck open it will be continuously short circuiting and you'll never get anywhere close to working pressure at your motor/cylinder regardless of what your pressure pump is putting out.

There's definitely one in the circuit and you may have an additional one on your valve as well

The surest way to rule this out is to measure the pressure at your actuator (in your case hydraulic motor) when your valve is open. If you have full system pressure here you do not have a relief valve problem and you either have a bad hydraulic motor or a blockage somewhere in the motor output to the tank or incorrect plumbing. If you don't then it could be a number of things like blockages on the input side or incorrect plumbing or relief valve stuck open.

 

[r8f1k]

If you look at the second photo I posted, there are two small caps that are on the bottom of each spool. I pulled those two out and you can push on a rod that makes the levers move. However, they are sticky and don't always return to the home position. I have solvent siting in the caps now and I am working the rods a little at a time until they free up. Hopefully this will do it.

 

[laurencen]

if it were me I would take the valve totally apart and give it a good cleaning, you mentioned water in the system, the valve body is cast iron and spool chromed steel, it will rust together sitting in water, they need to be taken apart and cleaned

 

[r8f1k]

Any recommendations on what chemicals to NOT use?

 

[laurencen]

we use diesel fuel, Varasol is good but ut takes oil out the cast, get some brass brushes, they sell ones for bores work great in cavities holes

 

[r8f1k]

I let the spools soak in HOT water and degreaser. I took as much apart as I could, the longer it sat, the looser it got. 2 out of the 3 will return with ease to the 'home' position. One is still a little sticky, so I have it sitting overnight in degreaser again. Lots of compressed air and moving the valves seems to have made a difference. I plan on dipping it again in the solvent tank and giving it a good cleaning in there. I think I will give it run tomorrow sometime in the afternoon. I will report.

 

[r8f1k]

I let the spool soak, took as much of it apart as I could, no change. Nothing. No hum, no shudder, not a thing. Must be something else. Not sure what to do.......I am also not sure what to do about the trencher pump/motor situation. I am tempted to pull the console again and remove the pump entirely and see if the roll pins, as mentioned, are broken or fell out. Another thought I have is, are the control cables adjusted properly? Is there the potential that the actuator cables are misadjusted and things are not being pulled or pushed as they should?

 

[r8f1k]

Any ideas? I had the thought of removing the existing pump and putting in a new unit. Just a regular direct drive pump and plumbing it to another spool. Use a spool for chain direction. Any thoughts?

 

[r8f1k]

Something like this.

 

[oldnslo]

R8
Picture in post 89 looks like a low speed high torque geroler or gerotor style motor. Is this what is on the trencher?

Have you done any testing on the trencher pump? Don’t recall who posted them but there were some suggestions on how to isolate and test the pump.

 

[r8f1k]

I have tested the pump with a pressure gauge, it holds 100 psi, it simply shudders between 80 and 100 psi when the lever is pulled to engage the trencher motor. The type of pump in post 89, is VERY similar to the pump that is in the unit currently. I am wondering if I could simply re-plumb the system with a simpler system of just a pump and a bidirectional control spool for the motor. I have plenty of hydraulic hose and my own crimping machine. I would also skip trying to use the backfill blade, I would take it off and eliminated it altogether. If someone could help me determine what kind of pump to swap in and what kind of spool would work.

 

[oldnslo]

Do you know the displacement and operating pressure of the existing pump? To get similar performance you need a pump with similar specs.

for the valve I would recommend a 3 position with motor spool rated for flow and pressure of that function.

 

[r8f1k]

The pump I have has a tag on it:
18-2081R LH
87-11-80260

I think it is Case part number:
H672705

Not sure how many splines are on it.....I can pull it and find out, any ideas of how one would properly plumb it? A simple hand drawing would be fine.

 

[r8f1k]

Do you know the displacement and operating pressure of the existing pump? To get similar performance you need a pump with similar specs.

for the valve I would recommend a 3 position with motor spool rated for flow and pressure of that function.

I already have this on hand:

https://www.amazon.com/Prince-RD512CA5A4B1-Directional-Control-Positions/dp/B0025PKDI2/ref=pd_lpo_2?pd_rd_w=lOsUk&content-id=amzn1.sym.116f529c-aa4d-4763-b2b6-4d614ec7dc00&pf_rd_p=116f529c-aa4d-4763-b2b6-4d614ec7dc00&pf_rd_r=3DT220WMYC8ZJ3J9DQJZ&pd_rd_wg=mzCsp&pd_rd_r=9da08fd7-bfb3-4e1f-8732-09249c70f8f7&pd_rd_i=B0025PKDI2&psc=1

I just need the pump.......

 

[r8f1k]

Does anyone know if all hydraulic pumps that have 13 spline shafts are the same diameter? Based on the Danfoos information for my Series 18-2081 pump, it has a 13 spline shaft. Just so I don't have to yank the pump out again, if I knew that most pumps were generally the same, I would order something like this:

Hydraulic Gear Pump 13 Tooth Spline Shaft CID 0.97 - 2.74 SAE B-2 bolts GPM 3-29 | eBay

Find many great new & used options and get the best deals for Hydraulic Gear Pump 13 Tooth Spline Shaft CID 0.97 - 2.74 SAE B-2 bolts GPM 3-29 at the best online prices at eBay! Free shipping for many products!

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Then plumb it to the system as best I can and run it to a spool valve with a detent.
Thoughts?

 

[oldnslo]

Yes 13 tooth spline is a standard for SAE - B.

Some things to consider on this trencher drive:
The current hydrostatic drive provides infinite speed adjustment of the trencher chain. Also allows feathering in both forward and reverse direction if trying to position a tooth to work on it.

• With hydrostatic drive typically if pump is bad the motor will also be bad since the debris circulates between the two components.
• With gear pump and detent valve you have one speed.
• Yes you can probably feather the chain into position but would be very challenging to try and hold a slower speed without a priority flow control in the circuit.
• what pressure does existing pump operate at? Will the gear pump be able to achieve the same pressure?

 

[r8f1k]

Given that the pump I have is Series 18-2081, how does one figure out if it is SAE-B?

 

[oldnslo]

Given that the pump I have is Series 18-2081, how does one figure out if it is SAE-B?

either find a detailed model code break down on the the current unit or take existing pump of and measure it. SAE - B is 4 inch diameter pilot 5.75 inches between mounting bolts.

 

[r8f1k]

Do you know the displacement and operating pressure of the existing pump? To get similar performance you need a pump with similar specs.

for the valve I would recommend a 3 position with motor spool rated for flow and pressure of that function.

1 Spool Hydraulic Directional Control Valve Motor Center 13 GPM 3600 PSI NEW! | eBay

Find many great new & used options and get the best deals for 1 Spool Hydraulic Directional Control Valve Motor Center 13 GPM 3600 PSI NEW! at the best online prices at eBay! Free shipping for many products!

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Would this work? I would like to get a spool that can hold in one position while the trencher is running. I assume a detent is needed? Anything specific to look for on the nomenclature of a spool?

 

[oldnslo]

That valve is not detented per the provided description. With out detent you would have to hold the valve shifted to keep chain spinning.