×
INTELLIGENT WORK FORUMS
FOR ENGINEERING PROFESSIONALS

Log In

Come Join Us!

Are you an
Engineering professional?
Join Eng-Tips Forums!
  • Talk With Other Members
  • Be Notified Of Responses
    To Your Posts
  • Keyword Search
  • One-Click Access To Your
    Favorite Forums
  • Automated Signatures
    On Your Posts
  • Best Of All, It's Free!
  • Students Click Here

*Eng-Tips's functionality depends on members receiving e-mail. By joining you are opting in to receive e-mail.

Posting Guidelines

Promoting, selling, recruiting, coursework and thesis posting is forbidden.

Students Click Here

Jobs

minimum test of faulty servo valve
2

minimum test of faulty servo valve

minimum test of faulty servo valve

(OP)
Hi
I'm having a problem with a hydraulic teststand and have a suspicion that it might be because of a faulty servo valve.  As we have plenty of oilsupply and a good cooling system the leakage isnt really a problem. My question now is if I just want to check if the valve is faulty and dont care what exactly is the reason of the faulty valve, what tests should be made as a minimum? I have an idea that a null test and a dynamic test would be enough but as my knowlege in the world of hydraulics is not that great I would like to know your oppenion
(If something like this thread is already out there I'm sorry to repost)

Best regards
Hans H.

RE: minimum test of faulty servo valve

(OP)
Oh I forgot to mention that the valves used in the stands are MTS 252.24C and mts 252.25C. I dont know if its relevant but now you know :)

RE: minimum test of faulty servo valve

Is the oil clean?

By clean, I mean clean to the required NAS or ISO 4406 standards for servo valves.

Are you getting position feedback from the valve? Does the feedback change in relation to the command signal?

Contamination will cause the spool/solenoid sleeve to stick.

RE: minimum test of faulty servo valve

(OP)
Hi again and thanks for the fast reply
As fare as I can tell the filters are working and the oil is not contaminated but I haven't used the teststand for a while so it might have been at some point. If this might be the problem a sticky spool would result i an abnormality when compared to a new valve right?  
As the problem started after i came back from holiday I have a suspicion that one of two things has happened:   

1: Someone have forgot about the cooling system so the system has reached a temperature higher than what the valve is rated for  

2: The supply pressure have been to high at some point   

It is obvious that these two things could be a reason for the error but I dont know exactly what kind of trouble they would result in and if I can see it from a dynamic test

 

RE: minimum test of faulty servo valve

What pressure does the system operate at?  I've seen some sticky valves that did not function properly at operating pressure, but upon lowering the pressure the valve operated normally.  This was due to the valve clearances being very tight and at the lower pressure, the clearances were acceptable for proper operation, but at the higher (operating) pressure, the spool would hang up on the sleeve.

The problem came from the wrong process in manufacturing where the sleeve and spool were fitted at a lower pressure than operating.

Is it possible to vary flow rate and pressure?  How about disassembling the test stand and checking the flow through the valve in either the open or closed position?

RE: minimum test of faulty servo valve

The MTS servo valves are made by Moog. Supposedly they have some special tweaks beyond the normal Moog items, but I have never found out what. These two valves are rated at 10 and 15 gpm at 3000psi.

I don't know if overly high pressure would cause operation like that. But if the oil got too hot it could have caused varnish and deposits. MTS is very particular about the oil, and STONGLY recommends Mobil DTE 25 because over time it has proven resistant to varnish formation.

As far as cleanliness goes you should keep the oil cleaner than an ISO 4406 rating of 16/13/9. It is possible that you have some particle stuck inside the valve.

As far as a check goes, the easiest one is the do a continuity check on the coils. Look for oil in the connector or broken wired in the connector back shell. If you do not have a known good valve to substitute (or a bunch of pressure and flow gauges) than the best thing to do is send it to any number of servo repair shops.

ISZ

Red Flag This Post

Please let us know here why this post is inappropriate. Reasons such as off-topic, duplicates, flames, illegal, vulgar, or students posting their homework.

Red Flag Submitted

Thank you for helping keep Eng-Tips Forums free from inappropriate posts.
The Eng-Tips staff will check this out and take appropriate action.

Reply To This Thread

Posting in the Eng-Tips forums is a member-only feature.

Click Here to join Eng-Tips and talk with other members!


Resources