Matronics Email Lists :: View topic

Matronics Email Lists
Web Forum Interface to the Matronics Email Lists

Get Email Distribution Too! FAQ Search Memberlist Usergroups Register

Profile Log in to check your private messages Log in

pitot system leaks

Matronics Email Lists Forum Index -> RV-List

View previous topic :: View next topic

Author Message

sarg314(at)gmail.com
Guest

Posted: Sun Jul 08, 2012 8:20 pm Post subject: pitot system leaks

I tested the pitot system (using the water in a U-shaped tube method) in my RV-6A today and found it leaking fairly badly.Â  Tightening up the various fittings helped.Â  I'm always afraid of over-tightening those plastic fittings.Â  That improved things but it still leaks down the airspeed indicator from about 106 to 100 knots in a couple of minutes.Â  I assume it should be able to hold constant for many minutes?

 

Do people ever use any kind of sealant on these fittings? A thin film of oil on the sealing surfaces perhaps?

-- 

Tom Sargent

  [quote][b]

n801bh(at)netzero.com
Guest

Posted: Sun Jul 08, 2012 8:47 pm Post subject: pitot system leaks

Loosing 6 Knots over a couple of minutes will not affect the accuracy of the ASI to any measurable degree. IMHO 

do not archive

Ben Haas

N801BH

www.haaspowerair.com



--------

vanremog(at)aol.com
Guest

Posted: Sun Jul 08, 2012 10:17 pm Post subject: pitot system leaks

First of all, what types of fittings are you using?  The best ones have intimate sealing surfaces or ferrules.

 

   What is the nature of the sealing surfaces?  They should be smooth and contiguous.

    

   Are you sealing to the inside diameter of the tubing or the outside?  Inside must mate with beaded or multi barbed fittings.

    

   Are there threads in the potential leak path?  If yes then use PST.

    

   -GV

    

   

 

  

   --

vanremog(at)aol.com
Guest

Posted: Sun Jul 08, 2012 10:22 pm Post subject: pitot system leaks

 	  Quote: 	
		  Are you sealing to the inside diameter of the tubing or the outside?  Inside must mate with beaded or multi barbed fittings. 	


   Sorry, this should have been completed as:  Outside must be absolutely flawless and slick to seal with O-ring fittings and a little DC4 couldn't hurt.

    

   -GV

 

 

 

   --

carl.froehlich(at)verizon
Guest

Posted: Mon Jul 09, 2012 2:54 am Post subject: pitot system leaks

The leak spec for the static system is to draw a vacuum to indicate 1000' above elevation and hold.  The altimeter should not drop more than 100' in one minute.

After chasing my tail to find a static leak on my 8A, I finally checked each instrument separately with the panel on the bench.  I found the face plate on the air speed indicator to be the source of the leak (the static port on the air speed indicator just connects to the case).  To do this ASI leak test, connect your manometer to a "T", then a line to both the pitot and static connectors.

A simple field fix is to use a very small amount for RTV around the glass perimeter.  The more elaborate fix is to send it to an avionics shop - but that will most likely be more expensive than just replacing the ASI.

Carl



On Jul 9, 2012, at 2:21 AM, vanremog(at)aol.com (vanremog(at)aol.com) wrote:



[quote]

     	  Quote: 	
		  Are you sealing to the inside diameter of the tubing or the outside?  Inside must mate with beaded or multi barbed fittings. 	


   Sorry, this should have been completed as:  Outside must be absolutely flawless and slick to seal with O-ring fittings and a little DC4 couldn't hurt.

    

   -GV

 

 

 

   --

sarg314(at)gmail.com
Guest

Posted: Mon Jul 09, 2012 7:45 am Post subject: pitot system leaks

The pitot system follows the plans. Van's pitot tube with aluminum fitting to AL tubing which then mates to poly tubing which then connects to instruments using nyloseal fittings.Â  I could tighten many of the nyloseal fittings with my fingers - so I did.Â  I suspect the leaks are at the point where the fittings screw into the instruments.

 

On Mon, Jul 9, 2012 at 3:51 AM, Carl Froehlich <carl.froehlich(at)verizon.net (carl.froehlich(at)verizon.net)> wrote:

[quote] The leak spec for the static system is to draw a vacuum to indicate 1000' above elevation and hold. Â The altimeter should not drop more than 100' in one minute.

 After chasing my tail to find a static leak on my 8A, I finally checked each instrument separately with the panel on the bench. Â I found the face plate on the air speed indicator to be the source of the leak (the static port on the air speed indicator just connects to the case). Â To do this ASI leak test, connect your manometer to a "T", then a line to both the pitot and static connectors.

 



A simple field fix is to use a very small amount for RTV around the glass perimeter. Â The more elaborate fix is to send it to an avionics shop - but that will most likely be more expensive than just replacing the ASI.

 



Carl



On Jul 9, 2012, at 2:21 AM, vanremog(at)aol.com (vanremog(at)aol.com) wrote:



[quote] 

     	  Quote: 	
		  Are you sealing to the inside diameter of the tubing or the outside?Â  Inside must mate with beaded or multi barbed fittings. 	


   Sorry, this should have been completed as:Â Â Outside must be absolutely flawless and slick to seal with O-ring fittings and a little DC4 couldn't hurt.

   Â 

   -GV

 

 

 

   --

Kellym

Joined: 10 Jan 2006
Posts: 1705
Location: Sun Lakes AZ

Posted: Mon Jul 09, 2012 8:08 am Post subject: pitot system leaks

The pitot system does not need to be as leak free as the static system.  

Small leaks have little effect on the airspeed indication. It operates 

at very low pressure, a few inches of water.  The static system is the 

only one that needs to meet the standard below.

Kelly

On 7/9/2012 8:44 AM, thomas sargent wrote:

[quote] The pitot system follows the plans. Van's pitot tube with aluminum 

 fitting to AL tubing which then mates to poly tubing which then 

 connects to instruments using nyloseal fittings.  I could tighten many 

 of the nyloseal fittings with my fingers - so I did.  I suspect the 

 leaks are at the point where the fittings screw into the instruments.



 On Mon, Jul 9, 2012 at 3:51 AM, Carl Froehlich 

 <carl.froehlich(at)verizon.net <mailto:carl.froehlich(at)verizon.net>> wrote:



     The leak spec for the static system is to draw a vacuum to

     indicate 1000' above elevation and hold.  The altimeter should not

     drop more than 100' in one minute.



     After chasing my tail to find a static leak on my 8A, I finally

     checked each instrument separately with the panel on the bench.  I

     found the face plate on the air speed indicator to be the source

     of the leak (the static port on the air speed indicator just

     connects to the case).  To do this ASI leak test, connect your

     manometer to a "T", then a line to both the pitot and static

     connectors.



     A simple field fix is to use a very small amount for RTV around

     the glass perimeter.  The more elaborate fix is to send it to an

     avionics shop - but that will most likely be more expensive than

     just replacing the ASI.



     Carl



     On Jul 9, 2012, at 2:21 AM, vanremog(at)aol.com

     <mailto:vanremog(at)aol.com> wrote:



>

>         Are you sealing to the inside diameter of the tubing or the

>         outside? Inside must mate with beaded or multi barbed fittings.

>

>     Sorry, this should have been completed as:  Outside must be

>     absolutely flawless and slick to seal with O-ring fittings and a

>     little DC4 couldn't hurt.

>     -GV

>     --

_________________
Kelly McMullen
A&P/IA, EAA Tech Counselor # 5286
KCHD

khorton02(at)gmail.com
Guest

Posted: Mon Jul 16, 2012 7:59 am Post subject: pitot system leaks

On 2012-07-16, at 11:39 , thomas sargent wrote:



 	  Quote: 	
		   I am still getting no where in testing my static system (or the static system leaks horribly).  Does the connection to the VSI have to be sealed off before testing?

 

 I tried bonding a vinyl tube (perpendicular)  to a piece of heavy clear plastic packing tape with GE silicone sealer. I cut a hole in the tape to open it to the tube and then pressed that onto the fuselage with the opening over the static port.  I put a piece of packing tape over the other static port and sucked on the tube.  I could get the altimeter and VSI to respond OK, but couldn't hold a deflection at all.  I had to keep sucking a lot of air thru the tube.  Air might have been leaking around the rivet that forms the static port where it penetrates the fuselage.   When I stick the tape+tube down to a flat smooth metal surface, it seems to seal well.  

 

 Some one said they used a veterinary syringe to draw a vacuum. How did you get that to seal to the static port?  The opening in the port is 1/16". All of the syringes I have are significantly larger than that.

 

 

There is no need to seal off the VSI.  But any of the pitot-static flight instruments could have a leak.
	




It may be easiest to go at this piecemeal, only testing a small part of your system at a time so you can narrow down where the leak might be.  You could disconnect and plug the forward end of the static line that comes from the rear fuselage to the instrument panel.  Then see if you still have a leak.  Then try a leak check on just the instrument panel portion of the system to see if that part is OK.



--

Kevin Horton

Ottawa, Canada

jconnell(at)fmwildblue.co
Guest

Posted: Tue Jul 17, 2012 6:39 am Post subject: pitot system leaks

The vertical velocity indicator needs to be clamped or blocked.  That  instrument has a â€œcalibratedâ€ leak in it.  Itâ€™s the difference between the  calibrated leak and pressure coming from the static port as the plane ascends or  descends that cause the needle to deflect.  As the plane continues to  ascend or descent there will continue to be a pressure differential.  Once  the plane levels off the static pressure becomes constant.  The calibrated  leak will then slowly match the static pressure and the needle will slowly  return to zero.  If there is no calibrated leak, the VSI would act like an  altimeter...

  

 Joe Connell

 Stewartville, MN

  

 Time: 08:40:12 AM PST US

Subject: Re: pitot system  leaks

From: thomas sargent <sarg314(at)gmail.com (sarg314(at)gmail.com)>



I am still  getting no where in testing my static system (or the static

system leaks  horribly). Does the connection to the VSI have to be sealed

off before  testing?

   [quote][b]

khorton02(at)gmail.com
Guest

Posted: Tue Jul 17, 2012 7:09 am Post subject: pitot system leaks

The "calibrated leak" in the VSI is internal to the VSI.  It is not a leak between the VSI and ambient pressure.  The only way air can get into or out of a serviceable VSI is at the connection to the static system.



There is no need to disconnect the VSI to do a static system leak check.  I just had my system checked by an avionics shop a few weeks ago.  It passed with zero leaks, without disconnecting anything.



Kevin Horton



On 2012-07-17, at 10:38 , <jconnell(at)fmwildblue.com> wrote:



 	  Quote: 	
		   The vertical velocity indicator needs to be clamped or blocked.  That instrument has a “calibrated” leak in it.  It’s the difference between the calibrated leak and pressure coming from the static port as the plane ascends or descends that cause the needle to deflect.  As the plane continues to ascend or descent there will continue to be a pressure differential.  Once the plane levels off the static pressure becomes constant.  The calibrated leak will then slowly match the static pressure and the needle will slowly return to zero.  If there is no calibrated leak, the VSI would act like an altimeter...

  

 Joe Connell

 Stewartville, MN

  

 Time: 08:40:12 AM PST US

 Subject: Re: pitot system leaks

 From: thomas sargent <sarg314(at)gmail.com>

 

 I am still getting no where in testing my static system (or the static

 system leaks horribly). Does the connection to the VSI have to be sealed

 off before testing?

n320wt(at)yahoo.com
Guest

Posted: Tue Jul 17, 2012 7:51 am Post subject: pitot system leaks

Good point, static system instruments AI, Alt and VSI are closed systems. Otherwise they would not work in a pressurized aircraft. There should not be anything disconnect during calibration, but troubleshooting a problem is a different situation!

Sent from my iPhone

Brian Alley

carbonfibercomposites.net

304-395-4932

On Jul 17, 2012, at 11:08 AM, Kevin Horton <khorton02(at)gmail.com> wrote:

 	  Quote: 	

 The "calibrated leak" in the VSI is internal to the VSI.  It is not a leak between the VSI and ambient pressure.  The only way air can get into or out of a serviceable VSI is at the connection to the static system.

 There is no need to disconnect the VSI to do a static system leak check.  I just had my system checked by an avionics shop a few weeks ago.  It passed with zero leaks, without disconnecting anything.

 Kevin Horton

 On 2012-07-17, at 10:38 , <jconnell(at)fmwildblue.com> wrote:

> The vertical velocity indicator needs to be clamped or blocked.  That instrument has a â€œcalibratedâ€ leak in it.  Itâ€™s the difference between the calibrated leak and pressure coming from the static port as the plane ascends or descends that cause the needle to deflect.  As the plane continues to ascend or descent there will continue to be a pressure differential.  Once the plane levels off the static pressure becomes constant.  The calibrated leak will then slowly match the static pressure and the needle will slowly return to zero.  If there is no calibrated leak, the VSI would act like an altimeter...

> 

> Joe Connell

> Stewartville, MN

> 

> Time: 08:40:12 AM PST US

> Subject: Re: pitot system leaks

> From: thomas sargent <sarg314(at)gmail.com>

> 

> I am still getting no where in testing my static system (or the static

> system leaks horribly). Does the connection to the VSI have to be sealed

> off before testing?

>

jconnell(at)fmwildblue.co
Guest

Posted: Wed Jul 18, 2012 1:18 pm Post subject: pitot system leaks

â€œUpon further reviewâ€ I now realize my VSI analysis was in error.   Sorry about the bad scoop I was giving out, guys...

  

 Joe

  

  

 

Time: 08:09:33 AM PST US

Subject: Re: pitot system  leaks

From: Kevin Horton <[url=wlmailhtml:{786209CE-C84E-49C1-8527-87BDB40934B3}mid://00000073/!x-usc:mailto:khorton02(at)gmail.com]khorton02(at)gmail.com[/url]>

The  "calibrated leak" in the VSI is internal to the VSI. It is not a leak  between

the VSI and ambient pressure. The only way air can get into or out of  a serviceable

VSI is at the connection to the static system.



There is  no need to disconnect the VSI to do a static system leak check. I just

had my  system checked by an avionics shop a few weeks ago. It passed with  zero

leaks, without disconnecting anything.



Kevin  Horton



   [quote][b]

Display posts from previous:

	Matronics Email Lists Forum Index -> RV-List	All times are GMT - 8 Hours
Page 1 of 1

Jump to:

You cannot post new topics in this forum
You cannot reply to topics in this forum
You cannot edit your posts in this forum
You cannot delete your posts in this forum
You cannot vote in polls in this forum
You cannot attach files in this forum
You can download files in this forum