Cylinder Drift Allowance

[StumpyWally]

I just finished doing in-place drift tests on the hydraulic cylinders on my excavator, a 2005 NH EH80cs = Kobelco sk80cs. Here are my results:

As expected, my boom & arm cylinders have virtually NO drift, because the lock valves in the main valve chest are working as they should.
I was mainly concerned about the bucket & thumb circuits, since these do NOT have lock valves. As you can see, both circuits have some drift, but both have drift rates that are about 0.6mm / 5 minutes or less. (I've independently run piston bypass leakage tests to prove that there is no bypass leakage.)
While even this low rate of drift is annoying to the way I often use my excavator, note that the allowable rate of drift that came out of the service manual is SO huge (3mm / 5 minutes) as to be ridiculous in my opinion.

So, I'm curious as to what the allowable rate of drift is for anyone else's excavator?? it should be listed in your service manual in the "Maintenance & Test Procedure" section, or similar. Please post your allowances here.

And while you're at it, if you have any results of drift tests on your excavator, I would be interested to compare them to mine, so please also post them here.
Thank you...

 

[John C.]

I have looked at hundreds of excavators and drift rates are always checked as part of the appraisal process. Hydraulic cylinders are all designed to have some drift as it is the only way to lubricate the packings on the pistons. Three inches in a minute on a used excavator is common and is noticeable to the operator sitting in the seat but under the normal operation of an excavator is usually not much of a problem. If you are lifting and setting heavy items and need to be that sensitive you need to think about using a crane made for that purpose. Excavators are not cranes even though most people are using them as such.