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Air Leak
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mark.bitterlich(at)navy.m
Guest

Posted: Tue Oct 28, 2008 3:32 pm Post subject: Air Leak

Doug Sapp. 



By the way, your aircraft is NOT a YAK "W" model of any kind is it?

Like a YAK-52TW, or a YAK-52W ???  They use a totally different Pop off

valve that is uses a larger piston (in diameter) than the YAK-50, 52 or

Suke 26/29/31.  



The CJ piston is different in height and spring seating depth. I believe

I mentioned that it is unwise to use a YAK spring with a CJ piston, but

maybe not.  In any case... Yep, replace the spring.  



Mark



P.s.  Also,.... Ever consider that you might have a leak somewhere ELSE?

P.p.s.  What are you flying exactly?  Excuse me for not

remembering!!!!!!!!!



 



--

randmyak52(at)bellsouth.n
Guest

Posted: Tue Oct 28, 2008 3:37 pm Post subject: Air Leak

Steve are you certain that the leak is at the relief valve? Can you actually 

hear air escaping? If not the leak could be at another location. The gauges 

are sometimes prone to leak and other locations could be the problem. Just a 

thought!

---

mark.bitterlich(at)navy.m
Guest

Posted: Tue Oct 28, 2008 3:46 pm Post subject: Air Leak

 	  Quote: 	
		  Here are a couple of suggestions to start with ...



T1 - with the -50 main air valve OFF can you charge the main air bottle

from an external source to 50 kgf/cm2? 
	


 	  Quote: 	
		  Yes = air valve in parallel to air bottle (similar to -52) No - air

valve in series with air bottle (similar to -18T)
	




I have never tried that test EXACTLY, but I can tell you this for SURE.

Air goes from the external fill valve to the PRV whether the main air

valve is off or on.  There is a check valve between the external air

fill and the PRV because air can NEVER come out of the external fill

valve except for what is in the LINE.  I've tested this.  



LOGIC says that since air is present at the PRV when the main air valve

is open, and is NOT there when the main air line is CLOSED.  (FACT)

And that since there is AIR at the PRV when fed from the external fill

regardless of the position of the MAIN AIR VALVE, that logically the

tank should not fill with the main air valve closed.  In order for this

to be WRONG, there would have to be an air line with a check valve in

it, that came from the PRV and BY-PASSED the Main Air Valve.  Possible,

but not likely...but never tested.  But I will check this weekend.  



 	  Quote: 	
		  T2 - (as a confirmation) on performing T1 did the main & emergency air

pressures ultimately charge to the same 50kgf/cm2 >level (do this slowly
	


to avoid overcharging the emergency bottle in case the PRV regulation

assumption is incorrect) Yes >= PRV regulates main & emergency air

bottle pressure (similar to -1 No = PRV only regulates main air bottle

pressure >(similar to -52)



When I first owned the aircraft, both main and emergency bottles would

pressurize either from the engine, OR from the external fill valve to

exactly the same pressure.  If pressure was exceeded, the PRV would

open, and charging to BOTH cylinders would stop, again, either by engine

compressor or by external air source.  This was actually tested by

hooking an external air source to the snot valve and pressurizing the

aircraft.  It is WELL KNOWN that the 50 charges BOTH bottles from the

engine and the 52 does NOT.  The 52 charges the emergency bottle ONLY

from the external air source.  KNOWN FACT. 



Over time though, ... As in 700 hours of flight time, I have run into a

situation where the main bottle charges to 50 and the emergency bottle

charges to 60.  Not sure if it is a gage error, or something else weird.

I bled down the emergency air bottle to nothing... And then went flying

with the gear down.  The main bottle went to 50 and the emergency bottle

once again went to 60.  No idea for sure why it does this.  I need to

put a calibrated gage on the system with both reading zero and bring it

up with external air to determine which gage is reading correctly... One

or both.  I could do this again.. This weekend if it is important enough

to warrant. 



Mark

 	  Quote: 	
		   

 There is a check valve to keep air from back-flowing into the

compressor line and more past the PRV to prevent cross flow between the
	


main and emergency bottles. I am unsure of the one you refer to. Help! 

 	  Quote: 	
		   


	




Got that one covered Mark, it's the presence of a check valve downstream

of the air filter that I was looking out for ... as per above it may not

now exist!



Rob R.





Read this topic online here:



http://forums.matronics.com/viewtopic.php?p 10828#210828





Attachments: 



http://forums.matronics.com//files/yak_5218t_air_schematic_variance_591.

pdf

jan.mevis(at)informavia.b
Guest

Posted: Tue Oct 28, 2008 11:34 pm Post subject: Air Leak

In my Yak50, the emergency bottle is also always charged to a higher level

than the main bottle. I never understood why. The main circuit depletes to

some 40 kg/cm² when standing still. The emergency pressure always stays

high.  I have a new engine, with a new compressor, and all the lines have

been thoroughly checked. 



Jan



--

mark.bitterlich(at)navy.m
Guest

Posted: Wed Oct 29, 2008 12:39 pm Post subject: Air Leak

Jan, mine didn't use to do that.  Both gages matched perfectly.  Then one day that changed, and now the emergency bottle always goes higher than the main.  Honestly, I suspected the gage calibrations to be suspect.  I own a bottle with gage that can check to see exactly how much I am putting in there and if the gages match or not when fed from the external port, but .... Not sure what that is going to tell me either. 



My memory dimly recalls one gent mentioning that a check valve can cause this.  No idea which one!  



Mark

 



--

Mozam

Joined: 24 Nov 2006
Posts: 85

Posted: Wed Oct 29, 2008 1:43 pm Post subject: Re: Air Leak

 	  mark.bitterlich(at)navy.m wrote: 	
		  Doug Sapp. 



By the way, your aircraft is NOT a YAK "W" model of any kind is it?

Like a YAK-52TW, or a YAK-52W ???  They use a totally different Pop off

valve that is uses a larger piston (in diameter) than the YAK-50, 52 or

Suke 26/29/31.  



The CJ piston is different in height and spring seating depth. I believe

I mentioned that it is unwise to use a YAK spring with a CJ piston, but

maybe not.  In any case... Yep, replace the spring.  



Mark



P.s.  Also,.... Ever consider that you might have a leak somewhere ELSE?

P.p.s.  What are you flying exactly?  Excuse me for not

remembering!!!!!!!!!

-- 	




Mark,



Yes, it's -52TW.  Explains why it has the bigger piston (which was news to me...thanks)



Doug Sapp told me he has no springs.  



The leak is obvious (you can hear it, and see the bubbles with soapy water use).  I checked and found no other leaks.



I just ordered a new spring from Jill (at) M14.  I'll post the results!



Cheers,

Steve

mark.bitterlich(at)navy.m
Guest

Posted: Wed Oct 29, 2008 2:10 pm Post subject: Air Leak

For lack of a better term:  "Oh shit".  



Steve, a few years ago a fellow came by New Bern with a YAK-52TW that

needed a new cylinder on the engine.  While he was here, I spent a

number of hours going over the airplane and looking at the differences

between it, and a standard 52.  One way or another we got around to

adjusting his pop-off valve to set the air pressure correctly.  I told

him I had a spare piston and spring if he needed it.  



Well.. Not so fast.  When I went to look at the Pop Off Valve, or

Pressure Regulating Valve, (whatever the proper term is), I IMMEDIATELY

noticed this his valve was NOT the same as the ones I had worked on and

had spare parts for.  The YAK-52, 55, 50, CJ, Sukhoi 26, 29 and 31 all

have pretty much the same piston and spring, as long as you change them

as a pair.  The 52TW is DIFFERENT!  I have not a clue in the world as to

why this is, but my GUESS is that since the 52TW was actually (re)made

in a different country, they used a pop-off valve that they had on hand.

Heck, it could even be a BETTER one for all I know.  



The difference is in the diameter of the piston for SURE.  If you use a

piston from Doug or someone else, it is just going to go in there and

rattle around and it will NOT seal correctly.  This is why you are

having your problem.  



I see two answers... Aerostar in Romania for a new one, or... Find your

original and try to put a new "top" on it per se.  



And lastly, there is another alternative.  I can't remember if it was

Hubie Tolson's Suke 31 or Sergei Boriaks old 31, but one of them had an

AMERICAN MADE pressure relief valve.  This puppy was made from stainless

steel and had an adjustable pressure assy, with a pull ring relief

fixture.  I did some research on it, and found that a new one cost $800.

I quickly gave up on it after that, but .... It sure worked and it NEVER

goes bad (in comparison to what we have now anyway)  You might want to

go that route if all else fails.  



Bottom line though, that is why you are leaking, without a shadow of a

doubt.  



Mark Bitterlich

 



--

dsavarese0812(at)bellsout
Guest

Posted: Wed Oct 29, 2008 2:32 pm Post subject: Air Leak

"....my GUESS  is that since the 52TW was actually (re)made in a different country."   One small correction Mark.  The 52TW was also made in Romania at the  same Aerostar factory as the standard 52's.

 Dennis

  

 [quote]   ---

mark.bitterlich(at)navy.m
Guest

Posted: Thu Oct 30, 2008 12:06 pm Post subject: Air Leak

Roger that.  And the bottom line is I have no idea why they would use a

different diameter valve.  Dennis, have you run into this at all?



Mark

 



--

dsavarese0812(at)bellsout
Guest

Posted: Thu Oct 30, 2008 2:43 pm Post subject: Air Leak

Not really.  

 Dennis

  

 [quote]   ---

Mozam

Joined: 24 Nov 2006
Posts: 85

Posted: Mon Nov 10, 2008 5:42 pm Post subject: Re: Air Leak

OK guys,



Here's the follow up I promised.



My problem was the air leaking out entirely overnight.  But, my compressor had no problem pumping the system up to 5.5 as I flew it.  The only leak I could find was out the vent holes in the pop-off valve.  



I replaced the piston in the pop-off valve (it had lasted 700 hours) with one Cliff Coy sent me, which matched the original one exactly.  I *think* the one Cliff sent me was not new.  I suspect Cliff told me it wasn't *new*, but I missed that part.  I only heard what I wanted to hear...know what I mean?



Then I tried another "new" piston I bought from Doug Sapp.  It was very different from the original (smaller height and diameter) and leaked like a sieve.  I think it was a CJ piston.  Doug probably assumed I had a CJ.



So, I thought maybe the spring was weakened.



Finally, I replaced both the spring and piston with new parts from Jill at M-14P.  Worked perfect.



Don't know if it was a bad piston or spring, but since both together are less than $100, I suggest replacing both if your leak is out the pop-off valve vent holes..



Cheers,

Steve Dalton

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