Case DH4B Trencher/Backhoe Won't Spin Trenching Chain

[r8f1k]

What kind of pump did you purchase or is the 8.4 GPM & the 23.7 liters per minute? Reason for asking is usually flow at an RPM is fixed number for max.

Flow required depends on the hydraulic motor size and desired RPM of that motor.

The pump is 23.72 GPM @ 2000 RPM. I went with a large GPM thinking that the flow can be controlled via the spool should it have a flow control feature. I am looking to error on the side of more GPM since it is a cheap foreign made pump. The motor that turns the trencher chain, is VERY large. Its about the size of small car battery. I can't find the GPM on the old 18 Series pump, so again, I would rather have a little more pressure that I can turn down, than not enough. My logic may be flawed, given I have NO real hydraulic experience, just what I know through working on tractors, skid steers, forklifts, etc.....Most of the time it is a matter of swapping an old part for a new matching unit. This is an attempt to get 50% of the machine working in a respectable way that I can trench here and there as needed. It won't be used every day 5 days a week, so I am good with some imperfect solutions.

I appreciate all of the advice over the last couple months, without communities like this, I have often wondered how many other machines would sit DEAD or inoperable simply because the owners don't know how to repair them. I am very grateful to all of the members here who have spent time and effort to help me find a solution to a fix a machine they will never use. I find it so humbling that I am able to post a question and DECADES of knowledge is available simply by pounding a keyboard. I thank each and everyone of you, I am sure many of you have had a few moments reading my responses and have wondered "what the hell.....?". I thank you for allowing me to learn what I have learned so many times from each and everyone of you. The process of talking about the problems and attempting to find a solution, pushes me to keep going. Thank you again!

 

[oldnslo]

R8,
My Sauer Sundstrand CD rom from 1998 does not list the 18 series pumps so no help on size. I did find a parts break down but it it did not show any displacement info. The 15 series was 15 cc /rev but I can find nothing stating what the 18 series was.

 

[r8f1k]

R8,
My Sauer Sundstrand CD rom from 1998 does not list the 18 series pumps so no help on size. I did find a parts break down but it it did not show any displacement info. The 15 series was 15 cc /rev but I can find nothing stating what the 18 series was.

Me either, I couldn't find anything about the pump indicating GPM. I'm just guessing because of the tank volume, motor size and hose diameters.

 

[r8f1k]

R8,
My Sauer Sundstrand CD rom from 1998 does not list the 18 series pumps so no help on size. I did find a parts break down but it it did not show any displacement info. The 15 series was 15 cc /rev but I can find nothing stating what the 18 series was.

Any recommendations on a spool valve for under $150?

 

[oldnslo]

for $150 you might have to get standard spring centered valve and a bungee cord to hold lever in position while trenching or cobble some form of friction lock for the lever.

 

[r8f1k]

for $150 you might have to get standard spring centered valve and a bungee cord to hold lever in position while trenching or cobble some form of friction lock for the lever.

What should I expect to pay?

 

[r8f1k]

Attached is my rough diagram of the hydraulic system I am currently retro fitting. I need the lines drawn for what to attach where. Since the old pump had about 6 lines out and the new pump has 2 lines out, things are different. Take a peek at the diagram and if you can fill in any of the connections, feel free. If you can list what to put where, I can do that too. I do NOT have the spool yet, but it will be 4 ports, 1 in, 1 return, 2 work ports. I can make my own hoses, so send me your ideas!

 

[r8f1k]

for $150 you might have to get standard spring centered valve and a bungee cord to hold lever in position while trenching or cobble some form of friction lock for the lever.

Is this the one to buy?

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[oldnslo]

R8,
To verify the valve size what RPM does the pump spin at? You listed specs at 2,000 RPM but I am not sure if that is what the engine drive speed is or does the engine run at a higher or lower RPM which will change the pump flow.

Your plumbing circuit looks mostly correct. Not sure if you require two case drains from the trencher motor. Also will need to verify the new pump inlet hose size. You need a minimum of 1 1/2" ID for 23 GPM to keep the velocity reasonable and prevent pump cavitation.

 

[Doaaj50]

I have been unavailable for a while, so I am trying to get caught back up here.

I saw a couple of posts regarding the displacement of an 18 Series. The answer is 2.3 cu in or 37.7cc. If you are running this pump at 2000 RPM you would have a theoretical flow of 19.78 GPM.

A few other things to consider since you are changing the architecture.

1. You need to understand the low pressure side of the motor. Most closed circuit piston motors need some level of back pressure to keep them from failing. I would recommend something similar to what the old pump had for charge pressure. Around 100 PSI. You may get that due to pressure drop in the system, but it would be good to verify.
2. Be sure you are not going to overspeed the motor with the additional flow from the larger pump. If you can provide some data on the motor we could potentially see how close you are to the upper speed limit.