O-ring / seals replacement
 

This question is regarding all seals in general (0-rings, gaskets, etc.)

Unless the maintenance / service manual says to replace the seal if it is damaged, otherwise it can be reused, is it ok to not replace the seal if it was just replaced a few hours or days earlier?

Example - I replaced a hydraulic filter and it's seals with new ones as part of a routine maintenance check. Few days later due to some other defect arising related to hydraulic system, I am to remove and inspect the filter. Upon removing and inspecting the filter everything is ok. Should I reuse the same seals as I was the one who replaced it only a few days earlier and the aircraft is still undergoing the same maintenance check?

Of course the manual says to replace the seals all the time, but this is already done by myself a few days ago... And by some luck new seals are no longer in stock...

O-Rings should be replaced EVERY time.

Seal-oil plates can be reused, "on-condition".

ST

If the system has been operated Id be more worried about the filter you have re-fitted.

All filters I fit are expendable or cut in half for spectro-analysis.

Experience and common sense....

I agree with Golden Rivet about 'O' rings.
I'd always change metal or paper gaskets though.

An experience qualified LAE engineer should be able to make your own judgement because you are the one who sign the CRS.

If in doubt as in your case, change it to ease your worry.

Yup common sense, if the seal is in an environment where it crushes down on it I would replace it everytime, it's is common sense as you do not want it failing. To be honest, I change them all when disturbed as it is both good practice and safety. Same with stiff nuts and nylocks.

Changed every time.

Rubber has a shelf life and expiry dates / DOM need to be checked on the replacement item to ensure its still serviceable.

You obviously work in an nice warm hangar with large stock of spares.

Exactly, And after such deviation, when there's a big smokin' hole in the ground directly attributable to loss of fuel / oil / hydraulic fluid, whose door do you think they'll be knocking on ?

No, But I do know how to spell AOG !

ST

Well, Gentlemen, a fascinating range of answers.
The same scenario applies in the motor -Trade..... Rolls Royce (as was) scheduled an extremely short service life for hydraulic hoses (4 years)
and, from memory, there's 10 0r 12 on a Spirit! (suspension and brakes licensed from Citroen and using non-corrosive mineral oil)
So, when did you renew all flexy's on your Escort/toyota/whatever braking system? ( And they all use DOT 3/4/5 Brake fluid which is extremely hygroscopic and rusts the system from the inside )

I suspect that this is all about arse-covering...it has nowt to do with sensible service life but all about inducing paranoia in the user and generating a profit-stream for the equipment-maker..... of course Rolls breakdowns were rare...just about anything that was likely to age or wear was scheduled for a service-change with a reserve margin putting it in the Helicopter or space-shuttle league.

Instead of blindly following "'cos the schedule says so," could someone (other than those who say Common sense,- it isn't very common)
can we have a rational reason why a seal you replaced a couple of weeks ago, is suddenly no longer serviceable.....
do you suggest that if a maintenance -sequence involves, say, building-up, measuring,partial stripping, adjusting and reassembly.....you'd change ALL O-rings and seals EVERY time? that could entail a lot of "used" parts before the rebuild even got completed.

I am NOT advocating that manufacturer's schedules should be ignored, just curious about how many follow blindly and how many question the rationale.

As Fargoo has rightly said,.........." its not blindly following - it's best practice. Seals/O-rings cost pennies, not worth re-using to save a few pennies overall.'

I still couldn't see all the fuss about here. This question should not be ask here on an Engineering forum.

You as a licensed Aircraft Engineer is FULLY responsible to your action to sign a CRS. You as an LAE would bear the consequence for your action.

Of course, we may be talking about cowboy LAE.

Static seal I use my judgement.
Dynamic seal I change as matter of course.

BH

Question for the OP.....are you an engineer and if so, what are your qualifications ?......the reason for asking is quite simple...if you are an engineer, then your training was clearly lacking in some of the basics and if you are qualified and working on aircraft, then I suggest you consider a career option change....today, for example, would be a good time to start.

So... how about 'O' rings on engine oil level dipsticks, hydraulic reservoir, fluid de-icer tank and fuel filler caps? :)

Stevef raises an interesting point.....I'd venture to suggest these items are probably not mandated for "once-use" change....it stretches the realms of credulity to suggest that an o-ring should be changed EVERY time a dipstick is checked.

perhaps the most sensible judgement is Blackhand's......he's trained to understand the engineering judgement and does so....
I agree that O-rings are relatively cheap (though exhorbitantly -priced once they're "certified" as Aircraft components) however, like fuel in the bowser, airspace above you , etc. they're no damned good in a stores miles away on a public Holiday , with AOG and a perfectly serviceable component ready-fitted and ready for re-installation.

sometimes blind obedience can be set aside and skill,experience and common-sense allowed to prevail. Theory and practise are not necessarily the same thing....as I said before.....it doesn't cost the seat-polishing academics a bean to cover their backside, so they don't "allow" a skilled engineer's judgement -call. (bet they'd change their tune if stuck somewhere inhospitable without all the throwaway items on tap)

" ......he's trained to understand the engineering judgement and does so...."

And the rest of us, presumably, are not ?....:}

Why would I risk my livelihood and the lives of a hundred plus passengers and crew just to save a few minutes and a few bucks. If at all possible I change all o-rings, static or dynamic. The oil filler cap is the only exception off the top of my head, its changed by task card on a time basis. If I have no alternative but to reuse a o-ring I can defer its replacement for 1 day per my companies approved maintenance program.


"Note: If applied to an ETOPS aircraft, contact SEAMC to “TOP” defer the aircraft along with the1 day deferral. Refer to ETOPS Manual E05-00-12 for “TOP” procedures.
During maintenance, if the instructions require the replacement of an O-ring or seal and the part is not available:
(1) If the existing O-ring or seal is reused:
(a) Verify the existing O-ring or seal is not deformed, worn, torn or degraded.
(b) Create a 1 day deferral to have the discrepant O-ring or seal replaced.
(c) Perform a “leak check” as required.":)

So, there IS a "get out of jail card"
Funny how you're allowed to judge that it's fit for use, but 24 hrs. later it transmogrifies into a "do not fly , this could cause a catastrophy" item.

Sane logic and reasoning have gone out of the window....the desk-wallahs run the asylum and we all jump to their tune.

just questioning "the system" not arguing about sensible , scientific judgements, but annoyed at how some twit comes up with an ass-covering diktat which affects the whole world.........mandatory seat-belt scrappage, anyone?

Have you asked yourself, why, ONE manufacturer has decided that after a given number of years, the whole assembly is unserviceable, irrespective of storage, sunlight -exposure, atmosphere and straight-forward wear-and-tear.

Scenario
 

You find a hydraulic case drain filter popped during a turnround. You drop the filter and find it clean and the o ring looks good. Only then do you realise that the nearest o ring is 4 hours away. 200 pax in the terminal and a crew going out of hours..........What will you do??