Actuators keep leaking even after changing of parts

[samlloyd1881]

Hi guys.I'm in the marine industry and my company manufacture actuators for valves.We mostly use a reck and pinion concept. Recently, a few of our actuators are constantly leaking, even after they have been changed. Our Service Engineer found some scratch marks on the reck gear body.

The casualty are mostly single acting actuators which are operating at 130bar.We suspect it's due to particles in the hydrualic oil, and also the fact that the reck gear is chrome plating, not so good wear resistance.

Hope to get advise on whether the above is possible or there could be other factors as i am still a novice in this department.

 

[ScottyUK]

I guess what you mean is a 'rack' and pinion arrangement. 'Reck' isn't a word, at least not in the English language.

Where are the leaks occurring? Presumably the seal does run on a smooth portion of the actuator, not on the rack? Is this the scored area? Normally chrome in the hydraulics world is a hard chrome on a rod to give improved wear resistance. Have you analysed the particles? What are they composed of?

Can you post an image of the actuator? It's hard to visualise the configuration and you could identify the point at which the leak is occuring. There are a few FAQs on image posting. Here's one: faq238-1161

For future reference, there's a dedicated fluid power forum: forum1083 but the guys who post there will almost certainly see this so don't worry about it.



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If we learn from our mistakes I'm getting a great education!

 

[opairengineering]

More information needed...

Type of fluid, seals, filtration.
Contamination level of subject unit and upper acceptance level for the same.
Area of leak.
Condition of the "chromed" component (agree with poster above that hard chrome is applicable in almost every instance).
Pictures?

 

[ccw]

Please point to where the actuator(s) are leaking, and to where the engineer saw the scratches.

 

[samlloyd1881]

Hi guys,

Fluid is hyderaulic oil (Shell Tellus),seal is Buna N typed O rings.Contamination wise, not too sure as my Service Engineer did not check how badly contaminated was the HPU.

There were some scratches on the chromed rack.Which could be due to the hard chrome being in sufficient.

The leakage was from the chamber block(cylinder covers) and the pinion gear from the single acting actuator.

 

[hydtools]

Is the leaking fluid hydraulic oil or gear lube oil?

Is hydraulic oil showing up in the gear cavity?

Ted

 

[Cheddarcaveman]

Is this a pus/pull or rotary actuator?
You say your company manyfacturers these. What is your roll that you are having to ask these questions?
Can you post a cross section drawing indicating where these leaks are? Where are these actuators installed?

 

[budt]

What is the condition of the "O" Rings that are leaking?

Do the O" Rings have backup washers?

What is the "O" Ring material?



Bud Trinkel, Fluid Power Consultant
HYDRA-PNEU CONSULTING

 

[EdDanzer]

My guess is there are no bearing surfaces to take the side loads from the gear meshing. Do not use o-rings in this type of application for seals the dynamic movements are more than they are good for.

Ed Danzer

http://www.danzcoinc.com

http://www.dehyds.com

 

[Cheddarcaveman]

Er - hello samlloyd1881!! You posted your question on 24th. October. It is now 1st November. You have many questions to answer to help us to help you so WHERE ARE YOU?
It's no use posting problems on these forums if you then don't take any further interest or part in the following discussions!
We are trying to sort out this problem for you, but you are now a part of the problem, SPEAK TO US!! HELP US TO HELP YOU!!

 

[ccw]

@Chedder, he said "reck and pinion". I put up a Moog Flow torque drawing for talking purposes.

He should check the rotational load and mechanical stops for this application. He should also pass word back to OEM of his unit about these problems. When is the last time the OEM ran accelerated life tests at max pressure, max velocity with max rotational inertia banging against the acutuator heads or shaft ends for mechanical stops?

Scratches on the back side of the rack indicate a failure of the rack back up idler bearing, or bad lubrication between rack and pinion teeth causing the rack to want to climb up out of the pinion. The good rack and pinion units do not let the rack/pinion reaction side loads be taken up by the piston/shaft seals and bearings. Good reciprocating seals in the hydraulics are "U" cup viton, not Buna-N "O" rings. "O" rings in reciprocating sliding action should have back up rings as stated.