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Air Leak
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flatspins(at)gmail.com
Guest

Posted: Sun Oct 26, 2008 8:45 am Post subject: Air Leak

Folks,



Once again I am looking for your expertise.



My air system charges up nicely to 5.5 on the gauge while flying.   

Then when I shut down I can hear it leaking out the two small vent  

holes in the pop-off valve body.  Soapy water confirms this leak as it  

sits.  Within two days the system will completely leak out.



I have thoroughly cleaned the inside of the pop-off valve to a nice  

shine and tried two new pistons.  It still leaks.



Could this be caused by a weakened spring?  Your thoughts are greatly  

appreciated.



-Steve Dalton

dsavarese0812(at)bellsout
Guest

Posted: Sun Oct 26, 2008 8:47 am Post subject: Air Leak

Absolutely.

 Dennis

  

 [quote]   ---

randmyak52(at)bellsouth.n
Guest

Posted: Sun Oct 26, 2008 9:12 am Post subject: Air Leak

Steve:

  I have had some of the same problems with various YAKS. I have found that 

after time the rubber seal molded into the brass plunger recedes to the 

point that the metal surface of the plunger makes contacts with the seat, 

this prevents proper seating. I have not had much luck with just replacing 

the rubber, doesn't last very long. I have however on several occasions used 

this method. I recently ordered the spring and plunger new from Jill. this 

worked perfectly, however it cost something over $100.00. I use a scuba 

bottle at the fill port to adjust the valve. Just hook up the bottle, get 

the pressure you want, and tighten the valve until it stops discharging. 

This method avoids a lot of readjusting while looking for the proper 

setting. Ideal is this, it pops of at Approx. 5.5 while in flight, and 

bleeds back to 5.0 after shutdown.



                                                                             

                                                                             

        Robert

---

dsavarese0812(at)bellsout
Guest

Posted: Sun Oct 26, 2008 9:21 am Post subject: Air Leak

Robert,

 I believe Steve said he tried two new  pistons.  The new pistons that I have purchased come with the  rubber seals molded in.  Assuming the new pistons Steve purchased did come  with the seals molded in, the only thing left to replace is the  spring.

 Dennis

  

 [quote]   ---

randmyak52(at)bellsouth.n
Guest

Posted: Sun Oct 26, 2008 10:02 am Post subject: Air Leak

I do agree with that Dennis, I did solve my problem  with the new plunger and spring. Actually one should never replace the plunger  without a new spring. that thing really takes a beating eveytime you  fly.

 [quote]   ---

wlannon(at)persona.ca
Guest

Posted: Sun Oct 26, 2008 10:02 am Post subject: Air Leak

Dennis;

  

 The new piston usually does the job, with or  without a new spring.  The available adjustment allows for a large  variation in spring tension.

 In this case a very detailed inspection of the  valve seat is in order.  Pitting corrosion may have compromised the  seat.

  

 Walt 

 [quote]   ---

dougsappllc(at)gmail.com
Guest

Posted: Sun Oct 26, 2008 10:10 am Post subject: Air Leak

On 10/26/08, Robert Langford <randmyak52(at)bellsouth.net> wrote:

[quote] I do agree with that Dennis, I did solve my problem with the new plunger and

 spring. Actually one should never replace the plunger without a new spring.

 that thing really takes a beating eveytime you fly.

   ---

dougsappllc(at)gmail.com
Guest

Posted: Sun Oct 26, 2008 10:46 am Post subject: Air Leak

Guys,

My computer has a glitch in it today and my unfinished email seems to

have gone away,so I'll try this once again.

On a CJ:

Air comes from the compressor into the snot valve, out of the snot

valve and into the pop off valve assembly which is made up of the

pressure reducing valve and two check valves, (one inward facing check

valve on each side of it).  The pop off valve also has a center

leg/fitting which goes on to the air filter and then on into the

system and tank.  Isn't the 52 the same?  In order for Steve to be

draining his system would he not have to have a leaking check valve as

well as pop off valve problem?  How else could the air get back

through the system to the pop off valve??

I do have new CJ6 pop off valves in stock (at) $85.00 each.  While the

exterior is different than that used in the 52 TJ tells me that the

interrior parts are the same as used in the 52 style pop off valve.

Always Yakin,

Doug

On 10/26/08, doug sapp <dougsappllc(at)gmail.com> wrote:

[quote] On 10/26/08, Robert Langford <randmyak52(at)bellsouth.net> wrote:

> I do agree with that Dennis, I did solve my problem with the new plunger

> and

> spring. Actually one should never replace the plunger without a new

> spring.

> that thing really takes a beating eveytime you fly.

>   ---

Rob Rowe

Joined: 10 Jan 2006
Posts: 124
Location: Berkshire, UK

Posted: Mon Oct 27, 2008 2:35 am Post subject: Re: Air Leak

 	  Quote: 	
		  In order for Steve to be draining his system would he not have to have a leaking check valve as well as pop off valve problem? How else could the air get back through the system to the pop off valve?? 	




YAK-52s do not have the additional check valve between the PRV and the air filter, so if the PRV fails the main air leaks down too. 



While early DOSAAF schematics do show such a check valve it seemingly never made it into series production (ditto for having the emergency air fed from the PRV) ... for reasons only known to YDB.



Rob R.

mark.bitterlich(at)navy.m
Guest

Posted: Mon Oct 27, 2008 1:23 pm Post subject: Air Leak

That's a perplexing problem.  If the spring were weak, one would think

that the air pressure would never reach 55 atmospheres to begin with.

Typically that problem is caused by a bad seat on the piston where the

rubber gets worn down or torn.  You say you tried two new pistons?  Did

you REPAIR them or were they actually NEW?  Yes, ... Once you replace

the piston, the spring is the next thing to change.  It is POSSIBLE that

you have some damage or contamination to the little metal ring that the

top of the piston (where the soft rubber is) pushes against in the main

body of the pop-off valve assembly itself.  Remember that the piston is

pushed by a spring to where the front of it simply pushes against a HOLE

thus sealing it.  That "hole" has a little ridge around it, and if that

is marred, scratched, contaminated with a piece of old rubber, corroded,

etc., then you will have a constant leak, that no new piston or spring

will ever correct. 



Best I can think of!  



Mark Bitterlich

 



--

mark.bitterlich(at)navy.m
Guest

Posted: Mon Oct 27, 2008 1:33 pm Post subject: Air Leak

I told you that too!    Yes, your CJ inside parts will work in a YAK

as long as you replace the piston and the spring at the same time.  The

spring seating depth on the piston for the CJ is different than the YAK

so the spring is different too!  Thus it is not wise to use a CJ piston

and a YAK spring.  However, if you simply use both the spring AND the

piston from the CJ, it works like a champ, which I have done on a 50, a

52, and a Sukhoi 26 and 31.  



Doug, the 52 is different than even the 50 on the air system.  For

example, if I close the main air valve on my 50, it shuts off ALL the

air even to the pop off valve.  Thus imagine my surprise when I closed

the main air valve on the 52 and went to pull the cover off the pop-off

valve only to have 700 PSI of air come screaming out.  SURPRISE!  



Mark Bitterlich

 



--

Rob Rowe

Joined: 10 Jan 2006
Posts: 124
Location: Berkshire, UK

Posted: Mon Oct 27, 2008 7:13 pm Post subject: Re: Air Leak

 	  Quote: 	
		  ... the 52 is different than even the 50 on the air system. For example, if I close the main air valve on my 50, it shuts off ALL the air even to the pop off valve. Thus imagine my surprise when I closed the main air valve on the 52 and went to pull the cover off the pop-off valve only to have 700 PSI of air come screaming out. SURPRISE! 	




Mark,

I understand that, functionally, the -50 air charging system has the same configuration as a CJ. So regardless of whether the -50 main air valve is open or closed it's the check valve between the PRV & air filter that's protecting you when you work on upstream components. As you discovered without this check valve a -52 needs to be de-pressurised first.



Rob R.

keithmckinley

Joined: 11 Aug 2008
Posts: 434

Posted: Mon Oct 27, 2008 8:32 pm Post subject: Re: Air Leak

Don't we compensate for the different spring tensions with the adjusting nut?



Interestingly, I turned down my air pressure after a recent post about high air pressure in the main and emergency tanks. My pressure was set at 55 atm and I reset it to 45. I also removed and cleaned the "pop off' valve body, spring,  and installed a new piston. Since then I have had a similar leak/venting at engine shutdown until about 30-35 atm when it stops and holds steady. I even tried putting the old piston back in as the rubber on the new one looked a little thin and misaligned....no change.



Since my system holds air with the main air valve shut off you'd think that I might get the air bleeding down to that same 30-35 atm level when I turn the main air back on a day later but I don't.



In any case, I can't imagine it's the spring but it must be, or like Mark mentioned, maybe a small bit of contamination or pit on the sealing lip hmmm...



Keith

700HS

mark.bitterlich(at)navy.m
Guest

Posted: Mon Oct 27, 2008 8:34 pm Post subject: Air Leak

Rob,  you lost me here.  In my 50 I can turn off the air valve and work on anything in the aircraft.  Check valve or not.  For example, if I pull the pop off valve apart and then turn on the air valve, air WILL come out of the PRV.  If I turn it off, the pressure stops.  How does a check valve come into play here?  

 

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!  

 

In the 50, the emergency and the main air bottles are fed from the engine compressor.  Not so the 52.  Does the CJ fill both air bottles from the compressor as well?  

 

Mark



________________________________



From: owner-yak-list-server(at)matronics.com on behalf of Rob Rowe

Sent: Mon 10/27/2008 11:13 PM

To: yak-list(at)matronics.com

Subject: Re: Air Leak




 	  Quote: 	
		   ... the 52 is different than even the 50 on the air system. For example, if I close the main air valve on my 50, it shuts off ALL the air even to the pop off valve. Thus imagine my surprise when I closed the main air valve on the 52 and went to pull the cover off the pop-off valve only to have 700 PSI of air come screaming out. SURPRISE!


	




Mark,

I understand that, functionally, the -50 air charging system has the same configuration as a CJ. So regardless of whether the -50 main air valve is open or closed it's the check valve between the PRV & air filter that's protecting you when you work on upstream components. As you discovered without this check valve a -52 needs to be de-pressurised first.



Rob R.





Read this topic online here:



http://forums.matronics.com/viewtopic.php?p 10708#210708

dsavarese0812(at)bellsout
Guest

Posted: Tue Oct 28, 2008 4:12 am Post subject: Air Leak

Yes, the CJ does.

 Dennis

  

 [quote]   ---

dsavarese0812(at)bellsout
Guest

Posted: Tue Oct 28, 2008 4:16 am Post subject: Air Leak

I have a question pertaining to the new piston  and seals that posters are referring to.  Were these pistons and seals  new, still in the original brown wax paper, with original seals or are  these pistons ones where the rubber seal has been replaced and the piston has  been cleaned and polished?  There is a significant difference between the  two.

 Dennis

 [quote]   ---

keithmckinley

Joined: 11 Aug 2008
Posts: 434

Posted: Tue Oct 28, 2008 6:49 am Post subject: Re: Air Leak

Dennis,



Mine was not in a brown wrapping and in fact didn't look shiny at all. The rubber looked like it was painted on vs the one I was going to replace which had a solid looking symmetrical rubber piece.    



Keith

700hs

dsavarese0812(at)bellsout
Guest

Posted: Tue Oct 28, 2008 10:35 am Post subject: Air Leak

Where did you get it?

 Dennis

  

 [quote]   ---

Rob Rowe

Joined: 10 Jan 2006
Posts: 124
Location: Berkshire, UK

Posted: Tue Oct 28, 2008 11:24 am Post subject: Re: Air Leak

 	  Quote: 	
		  In my 50 I can turn off the air valve and work on anything in the aircraft. Check valve or not. For example, if I pull the pop off valve apart and then turn on the air valve, air WILL come out of the PRV. If I turn it off, the pressure stops. How does a check valve come into play here? 

	




Curiouser & curiouser ... the more I look into this the more variation I find ... this post carries an Anorak warning!



1 - I'm 99% sure of -52 air system functionality as I'm in possession of the schematics and it ties up with collective operational experience



2 - I cannot find a set of YDB issued Yak-50 original air schematics here in the UK, does anyone have these to share? So all I can get universal agreement to is that both the main & emergency bottles are fed from the PRV. Anecdotal info then conflicts about the presence of additional check valves and whether the main air valve isolates the main air bottle (as you describe Mark) or simply separates the air sources from air consumers (as per the -52). Perhaps YDB modified the -50s over time?



3 - YAK-18T schematics have the main air valve isolating the main air cylinder, which would produce the outcome you've described Mark so maybe your -50 is configured this way? Nb - I've no operational info to verify the -18T schematic is correct ... any -18T owners out there who can confirm this?



4 - seems YDB used the same air system components but in fundamentally different configurations across YAK 18Ts, 50s & 52s - see attached PDF showing 52/18T variance. It would be useful to add -50 version(s) to this with everyones help & CJs too (again can anyone post an original Nanchang air schematic?)



In the presumed absence of -50 schematics perhaps we can come up with some simple ground tests to determine air system function? 



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? 

Yes = air valve in parallel to air bottle (similar to -52)

No - air valve in series with air bottle (similar to -18T)



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 -18)

No = PRV only regulates main air bottle pressure (similar to -52)



 	  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! 

	




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.

YAK-52~18T Air Schematic Variance.pdf

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Mozam

Joined: 24 Nov 2006
Posts: 85

Posted: Tue Oct 28, 2008 2:50 pm Post subject: Re: Air Leak

Guys,



Here is more info and answers to several questions you asked.



Initially, the system would leak down to 3.0 to 3.5 and then hold there.  Gradually it began to completely leak out as time went on.  IOW, it slowly got worse.



I cleaned the inside of the valve to a nice shine...no corrosion or pitting.  Still leaked out.  Sometimes in less than a day, and other times it might hold pressure for a week or more.  Very erratic.



That's why I tried a new piston (from Cliff Coy), which made no difference at all.



Then I tried a new piston from Doug Sapp.  This piston was much shorter in height and appears to be slightly smaller in diameter (a CJ piston?).  It leaks like a sieve!



Surprisingly, even with these leaks, the system pumps up to 5.5 inflight, although it may be a little slow to pump up.



Because the valve interior appears clean and pit free, the leak is confirmed out the valve's vent holes, and I tried other pistons, the only conclusion I can reach is a weak spring.



The spring seems to hold enough pressure on the piston to allow the compressor to pump the system up (ie, a small leak the compressor overcomes), but not enough pressure when sitting to hold the piston tight in the valve.



So, anybody know where I can get a new spring, 'cause I'm out of ideas?



Thanks,

Steve

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