Help With Leak Test Results

[Frank]

Hi,

After reading as much as I could find, and assembling the necessary
tools, I have just started a leak testing program on my 1980 LS4.

I verified that my ASI is well sealed by creating sufficent vacuum on
the static input to show 100kt on ASI and observing no appreciable
airspeed decrease after several minutes.

After verifying the ASI, I used it to test my aft static lines. With
all 4 fuselage static ports blocked with tape, I T'd my 60cc syringe
into the static line, connected the assembly to the ASI and then pulled
suffient negative pressure to measure 100kt on the ASI. After clamping
off the syringe line I verified that the clamp worked by noting that I
could no longer change the ASI reading with the syringe, and then
recorded a 37kt ASI reading decrease over a 6 minute period (just over
6kt/minute)

My question is, do I need to start tearing up the seat pan and tracing
this line back into the fuselage, or is a 6kt/minute ASI reading
decrease OK?

One of the fine articles I read give a subjective threshold for
'goodness' but although the article talked about using the ASI as the
mesuring instrument, the stated threshold was "20ft/minute", (I'm
guessing they used the altimeter instead) ;-).

TIA,

Frank

[Doug Haluza]

No leak is good. You should see no appreciable movement if the system
is well sealed. The rate of leakdown is a function of the total volume
of the system, so it's hard to say what is OK.

Static leaks are not nearly as important as pitot leaks. The cockpit
pressure is close to static anyway, so a small leak has a very small
effect. A pitot leak is much more troubling because it will cause your
airspeed to read low. The higher the speed, the worse the error, so you
can easilly exceed Vne thinking you are well below red line. It can
also cause you to come in faster than expected, leading to an
overshoot.

To test the pitot side of the system, you need to use your syringe to
pressurize the pitot. Again, you should see no appreciable movement.

To fix the leaks, first make sure the tubing is still flexible. Then
you need to cut off the stretched ends, and reinstall the tubes. Do not
yank the tubes off because you can damage instruments like varios with
the sudden pressure spike. Cut the tubes off, but do not nick the
barbs.

But most important, you need to install tubing clamps over the barbs.
Without clamps, the tubes will leak. The best ones are the mini
stainless steel pinch clamps (you can crimp these with an end nipper
set of pliers). You can also use the nylon wraparound clamps, which are
reusable. Tie-wraps are not suitable because they leave a gap at the
right angle bend.

One other thing you can try to find the leak is bubble solution. You
can get plumbers bubbles from a plumbing supply or home center, or just
use your kid's bubble wand stuff.

Frank wrote:
> Hi,
>
> After reading as much as I could find, and assembling the necessary
> tools, I have just started a leak testing program on my 1980 LS4.
>
> I verified that my ASI is well sealed by creating sufficent vacuum on
> the static input to show 100kt on ASI and observing no appreciable
> airspeed decrease after several minutes.
>
> After verifying the ASI, I used it to test my aft static lines. With
> all 4 fuselage static ports blocked with tape, I T'd my 60cc syringe
> into the static line, connected the assembly to the ASI and then pulled
> suffient negative pressure to measure 100kt on the ASI. After clamping
> off the syringe line I verified that the clamp worked by noting that I
> could no longer change the ASI reading with the syringe, and then
> recorded a 37kt ASI reading decrease over a 6 minute period (just over
> 6kt/minute)
>
> My question is, do I need to start tearing up the seat pan and tracing
> this line back into the fuselage, or is a 6kt/minute ASI reading
> decrease OK?
>
> One of the fine articles I read give a subjective threshold for
> 'goodness' but although the article talked about using the ASI as the
> mesuring instrument, the stated threshold was "20ft/minute", (I'm
> guessing they used the altimeter instead) ;-).
>
> TIA,
>
> Frank

[HL Falbaum]

"Doug Haluza" > wrote in message
ups.com...
> But most important, you need to install tubing clamps over the barbs.
> Without clamps, the tubes will leak. The best ones are the mini
> stainless steel pinch clamps (you can crimp these with an end nipper
> set of pliers). You can also use the nylon wraparound clamps, which are
> reusable. Tie-wraps are not suitable because they leave a gap at the
> right angle bend.
>
Doug:
Do you have a brand name or source of supply for these?
Quick Google search does not yield the product you describe.
Thanks


Hartley Falbaum

[chipsoars]

I've found these at places like VWR, Fisher Scientific or Cole-Parmer.

Chip F

[chipsoars]

I've found these at places like VWR, Fisher Scientific or Cole-Parmer.

Chip F

[jcarlyle]

Here's a leak testing article that I found helpful:
http://www.borgeltinstruments.com/Leaks.pdf
Sure, it's commercial, but it gives a nice detailed procedure for leak
testing.

Note paragraphs 3 and 4 near the front. Mike recommends using rubber
donuts to prevent leaks (I thinking these donuts are similar to the
grommets used for feeding power cables into metal boxes). He also
concurs with Doug that cable ties or twisted wire are not good for
pneumatic systems.

-John

[Papa3]

http://www.mcmaster.com

Page 233 for pinch clamps

I think one day I will just buy all of the bits needed to build my own
glider from these guys - it's pretty much the default source for
anything that I can imagine needing.

P3

[bumper]

Yup, one of my goals in life is to be able to afford to call 'em and have
them ship me 6 of everything . . .

Seriously, placing an order with them is a problem, 'cause there's always
something you should have included in the order but forgot.

When you order the pinch clamps, don't forget to get a roll of UHMW
polyethylene tape. Great for anti-chafe etc. Their number is 76445A12 for
the 1" wide X .0065" X 18 yds.

bumper
"Papa3" > wrote in message
oups.com...
> http://www.mcmaster.com
>
> Page 233 for pinch clamps
>
> I think one day I will just buy all of the bits needed to build my own
> glider from these guys - it's pretty much the default source for
> anything that I can imagine needing.
>
> P3
>

[01-- Zero One]

"jcarlyle" > wrote in message
oups.com:

> Here's a leak testing article that I found helpful:
> http://www.borgeltinstruments.com/Leaks.pdf
> Sure, it's commercial, but it gives a nice detailed procedure for leak
> testing.
>
> Note paragraphs 3 and 4 near the front. Mike recommends using rubber
> donuts to prevent leaks (I thinking these donuts are similar to the
> grommets used for feeding power cables into metal boxes). He also
> concurs with Doug that cable ties or twisted wire are not good for
> pneumatic systems.
>
> -John



The donuts he talks about are like "O" rings. Roll them an inch or so
onto the tubing, place the tubing onto the barb then roll the donut back
over the connection. This gives good sealing pressure with no voids.



With good tubing and barbed connectors I have seen precious few leaks
without any sort of clamps. Once the tubing gets hard then, yes, you
could have a leak. If I were going to use any sort of clamps, I would
use donuts.



Larry

"01" USA

[Ken Ward]

those "donuts" are, in real life, used for castrating sheep (cheers to
those Australians for finding a second use for everything). however,
they make great tubing clamps. they will crack after a few years
exposure, but are cheap to replace.

the electric wire grommets have nearly no elastic properties.

Ken

In article >,
"01-- Zero One" > wrote:

> "jcarlyle" > wrote in message
> oups.com:
>
> > Here's a leak testing article that I found helpful:
> > http://www.borgeltinstruments.com/Leaks.pdf
> > Sure, it's commercial, but it gives a nice detailed procedure for leak
> > testing.
> >
> > Note paragraphs 3 and 4 near the front. Mike recommends using rubber
> > donuts to prevent leaks (I thinking these donuts are similar to the
> > grommets used for feeding power cables into metal boxes). He also
> > concurs with Doug that cable ties or twisted wire are not good for
> > pneumatic systems.
> >
> > -John
>
>
>
> The donuts he talks about are like "O" rings. Roll them an inch or so
> onto the tubing, place the tubing onto the barb then roll the donut back
> over the connection. This gives good sealing pressure with no voids.
>
>
>
> With good tubing and barbed connectors I have seen precious few leaks
> without any sort of clamps. Once the tubing gets hard then, yes, you
> could have a leak. If I were going to use any sort of clamps, I would
> use donuts.
>
>
>
> Larry
>
> "01" USA

[jcarlyle]

Sheep castraters, eh? That's well outside my life's experience! What
would be a source of supply for such a thing?

Wings & Wheels doesn't appear to offer anything similar (
http://www.wingsandwheels.com/page23.htm ). I also checked
McMaster-Carr ( http://www.mcmaster.com/ ) by putting o-ring into the
find box at the upper left. It comes up with a page with mind-numbing
information - multiple shapes, multiple sizes, materials, hardness,
etc.

Can you offer any guidance, Ken?

-John

[Eric Greenwell]

bumper wrote:
> Yup, one of my goals in life is to be able to afford to call 'em and have
> them ship me 6 of everything . . .
>
> Seriously, placing an order with them is a problem, 'cause there's always
> something you should have included in the order but forgot.
>
> When you order the pinch clamps, don't forget to get a roll of UHMW
> polyethylene tape. Great for anti-chafe etc. Their number is 76445A12 for
> the 1" wide X .0065" X 18 yds.
>
> bumper
> "Papa3" > wrote in message
> oups.com...
>
>>http://www.mcmaster.com

I also recommend getting some of their silicone tubing to connect your
instruments. I started using it when some came with my Cambridge vario a
few years ago. It is softer and more flexible the typical clear (but
often colored) plastic tubing and remains that way instead of hardening
over the years. That makes it easy to put it on the instrument, easy to
remove (just pull - no cutting required), and it doesn't need clamps to
prevent leaks.

Because the glider is plumbed in the usual clear tubing, you need to
transition from that to the silicone with a barbed fitting (straight,
tee, or cross, depending on how many things you want to connect to the
particular line). You could use a clamp on the original plastic line
tubing, but because it is never removed, I haven't had any problems with
leaks there.

It costs a bit more, but you can buy it from McMaster-Carr in short
lengths, so the price is not an issue.


--
Change "netto" to "net" to email me directly

Eric Greenwell
Washington State
USA

www.motorglider.org

[Robin Birch]

In message >, Eric Greenwell
> writes
>
>I also recommend getting some of their silicone tubing to connect your
>instruments. I started using it when some came with my Cambridge vario
>a few years ago. It is softer and more flexible the typical clear (but
>often colored) plastic tubing and remains that way instead of hardening
>over the years. That makes it easy to put it on the instrument, easy to
>remove (just pull - no cutting required), and it doesn't need clamps to
>prevent leaks.
>
>Because the glider is plumbed in the usual clear tubing, you need to
>transition from that to the silicone with a barbed fitting (straight,
>tee, or cross, depending on how many things you want to connect to the
>particular line). You could use a clamp on the original plastic line
>tubing, but because it is never removed, I haven't had any problems
>with leaks there.
>
>It costs a bit more, but you can buy it from McMaster-Carr in short
>lengths, so the price is not an issue.
>
>
I would also recommend putting springs over the silicone pipe if there
is any chance of a sharp bend coming up as it can collapse and
effectively seal the tube.

Robin

--
Robin Birch

[Martin Gregorie]

jcarlyle wrote:
> Sheep castraters, eh? That's well outside my life's experience! What
> would be a source of supply for such a thing?
>
Try a Stock & Station Agent from an American sheep-farming area. Sorry,
but I don't know American for "Stock & Station Agent".

In NZ the rings are called "emasculator rings", but the name may be
different in the US, especially if the PC pests have been at work.


--
martin@ | Martin Gregorie
gregorie. |
org | Zappa fan & glider pilot

[Eric Greenwell]

Robin Birch wrote:
> In message >, Eric Greenwell
> > writes
>
>>
>> I also recommend getting some of their silicone tubing to connect your
>> instruments. I started using it when some came with my Cambridge vario
>> a few years ago. It is softer and more flexible the typical clear (but
>> often colored) plastic tubing and remains that way instead of
>> hardening over the years. That makes it easy to put it on the
>> instrument, easy to remove (just pull - no cutting required), and it
>> doesn't need clamps to prevent leaks.
>>
>> Because the glider is plumbed in the usual clear tubing, you need to
>> transition from that to the silicone with a barbed fitting (straight,
>> tee, or cross, depending on how many things you want to connect to the
>> particular line). You could use a clamp on the original plastic line
>> tubing, but because it is never removed, I haven't had any problems
>> with leaks there.
>>
>> It costs a bit more, but you can buy it from McMaster-Carr in short
>> lengths, so the price is not an issue.
>>
>>
> I would also recommend putting springs over the silicone pipe if there
> is any chance of a sharp bend coming up as it can collapse and
> effectively seal the tube.

That doesn't seem necessary with the tubing I have, unless it is quite
sharp; for example, bending the tubing in a "U" that is 1.5" (measured
at the center of the tubing) across doesn't cause a problem. It has a
maximum temperature rating of 500 F, so cockpit temperatures won't be a
problem! The McMaster-Carr label on the bag it came in is says

Vanguard Products
Size: 3/16" (ID) x 5/16" (OD)
Material: translucent, 50 Duro silicone


Other types might be more prone to collapse, but this one seems quite
resistant.

--
Change "netto" to "net" to email me directly

Eric Greenwell
Washington State
USA

www.motorglider.org

[Doug Haluza]

Here is a link that shows both types of clamps. The prices do look a
bit high.

http://www.engineeringfindings.com/cat22/cat22pg130.pdf

The idea of using an O-ring as a seal sounds interesting. I have not
tried it, though.

[jcarlyle]

I did some research on this subject. Turns out that the proprietary
term is "elastrator ring", used with a device called (naturally) an
"elastrator" for castrating calves, goats and lambs. Mostly they are
green in color, but they also come in blue and orange in quantities of
100, 500 and 2000. Apparently there are two materials that they are
made from, with latex "expanding 170% more and gripping tighter" than
whatever the normal material is. I found no information about size; but
since Mike Borgelt has found that they work in our exact application
the question is settled.

In the USA you can find them at at veterinary and farm supply firms,
see ( http://shop.store.yahoo.com/animalmedicstore/cassup.html ). One
potential problem is that they are so cheap ($1.20 for 100) you might
run into a minimum order size problem if you mail order them.

Warning - if you're squeamish, don't investigate this subject too
thoroughly! There are some graphic pictures of these things in use,
plus painful descriptions of animals reacting to them. There's also
some kinky stuff on human use out there, too. You've been warned!

-John


Martin Gregorie wrote:
> jcarlyle wrote:
> > Sheep castraters, eh? That's well outside my life's experience! What
> > would be a source of supply for such a thing?
> >
> Try a Stock & Station Agent from an American sheep-farming area. Sorry,
> but I don't know American for "Stock & Station Agent".
>
> In NZ the rings are called "emasculator rings", but the name may be
> different in the US, especially if the PC pests have been at work.
>
>
> --
> martin@ | Martin Gregorie
> gregorie. |
> org | Zappa fan & glider pilot

[bumper]

Latex is a questionable material to use when there are much better
alternatives, from McMaster-Carr on latex:

Oil and flame resistance - poor
Weather and oxidation resistance - fair
Ozone resistance - poor

Like Eric, I've been using silicone tubing for the connection to instruments
for years. It retains its elasticity and is excellent in all three
categories; weather, oxidation, and ozone resistance.

Besides the options of using small hose cinch clamps or O-rings (silicon,
viton or EPDM resist weather well), MC also sells "Caps for Caulking
Tube/Glue Bottles. These are like miniature condoms and are designed to
unroll onto the tip of a bottle or applicator. They have great elasticity
(probably strong enough to cinch down even a relatively hard hose) and I
imagine would weather well also. To use them on a hose, one would cut off
the tip and roll them out on the hose, place hose over instrument nipple and
then roll cap back up onto nipple.

MC item number is 7526A11 $4.48 per package of 35 ea.

If you don't like 'em for hoses, you can always use them for sealing
caulking tubes (g).

bumper


"jcarlyle" > wrote in message
oups.com...
>I did some research on this subject. Turns out that the proprietary
> term is "elastrator ring", used with a device called (naturally) an
> "elastrator" for castrating calves, goats and lambs. Mostly they are
> green in color, but they also come in blue and orange in quantities of
> 100, 500 and 2000. Apparently there are two materials that they are
> made from, with latex "expanding 170% more and gripping tighter" than
> whatever the normal material is. I found no information about size; but
> since Mike Borgelt has found that they work in our exact application
> the question is settled.
>
> In the USA you can find them at at veterinary and farm supply firms,
> see ( http://shop.store.yahoo.com/animalmedicstore/cassup.html ). One
> potential problem is that they are so cheap ($1.20 for 100) you might
> run into a minimum order size problem if you mail order them.
>
> Warning - if you're squeamish, don't investigate this subject too
> thoroughly! There are some graphic pictures of these things in use,
> plus painful descriptions of animals reacting to them. There's also
> some kinky stuff on human use out there, too. You've been warned!
>
> -John
>
>
> Martin Gregorie wrote:
>> jcarlyle wrote:
>> > Sheep castraters, eh? That's well outside my life's experience! What
>> > would be a source of supply for such a thing?
>> >
>> Try a Stock & Station Agent from an American sheep-farming area. Sorry,
>> but I don't know American for "Stock & Station Agent".
>>
>> In NZ the rings are called "emasculator rings", but the name may be
>> different in the US, especially if the PC pests have been at work.
>>
>>
>> --
>> martin@ | Martin Gregorie
>> gregorie. |
>> org | Zappa fan & glider pilot
>

[Papa3]

bumper wrote:
> Yup, one of my goals in life is to be able to afford to call 'em and have
> them ship me 6 of everything . . .
>
> Seriously, placing an order with them is a problem, 'cause there's always
> something you should have included in the order but forgot.
>
> When you order the pinch clamps, don't forget to get a roll of UHMW
> polyethylene tape. Great for anti-chafe etc. Their number is 76445A12 for
> the 1" wide X .0065" X 18 yds.
>
> bumper

My office happens to be about 30 minutes away from their East Coast
warehouse, so I've driven down there on occasion. Talk about a kid in
a candy store - yikes. My wife sees about 2 packages a month from
there between glider fiddling and household projects . She was
beginning to wonder if I'd developed some substance abuse problem, but
all I had to do was mention the glider, and she just shook her head
knowingly.

P3

[jcarlyle]

I'm trying to pin this whole issue down a bit better. Using this web
site ( http://www.mcmaster.com/ ) I found that Eric's translucent, 50
Duro silicone tubing with 3/16" ID and a 5/16" OD is McMaster-Carr P/N
51135K23. It is $0.74 per foot for 10, 20, 50 and 100 foot lengths.

I think O-rings would work better than Bumper's caulking tube clamps,
because I think O-rings will have better quality control. McMaster-Carr
has a mind numbing selection, but specifying 70 Duro silicone rubber
O-rings with a 5/16" ID and a 3/32" width gives McMaster-Carr P/N
9396K74. They are $9.93 for a pack of 100.

What I'm not sure of is the optimal ID and wall thickness. I picked
5/16" OD so they would easily roll over the tubing above, and 3/32"
width because it would be slightly stronger than 1/16" while still not
much more expensive. However, a 1/4" OD with a 1/16" width would surely
hold tighter - but might it distort the tubing to the point of leaking?
I don't know - opinions?

-John

[Martin Gregorie]

jcarlyle wrote:
> I did some research on this subject. Turns out that the proprietary
> term is "elastrator ring", ......
> ...... Apparently there are two materials that they are
> made from, with latex "expanding 170% more and gripping tighter" than
> whatever the normal material is. I found no information about size;
It's a long time since I've seen them, but IIRC the hole is about 4.5mm
(3/16") and the ring is about 3mm (1/8") thick.

They all stretch a lot. As Todd says, they are also used to remove
lamb's tails and so must stretch far enough to be easily slipped over
the tail + wool in it. At a guess that means they will stretch to an ID
of at least 25mm (1"), so even the non-latex variety should do as the
tubing clamp.

> In the USA you can find them at at veterinary and farm supply firms,
> see ( http://shop.store.yahoo.com/animalmedicstore/cassup.html ). One
> potential problem is that they are so cheap ($1.20 for 100) you might
> run into a minimum order size problem if you mail order them.
>
If the applicator is not too expensive, you buy that to bulk up your
order. The ones I've seen have four wires coming out the business end
and bent at right angles to the plane of the grips. The wires are
normally all touching and a ring slides snugly over them. Squeezing the
grips separates the wires to expand the ring into a stretched square so
you could use it to place rings onto the tube.

You'll need something to stretch a ring so you can push the tube through it.


--
martin@ | Martin Gregorie
gregorie. |
org | Zappa fan & glider pilot

[Robin Birch]

In message >, Eric Greenwell
> writes
>Robin Birch wrote:
>>>
>>>
>> I would also recommend putting springs over the silicone pipe if
>>there is any chance of a sharp bend coming up as it can collapse and
>>effectively seal the tube.
>
>That doesn't seem necessary with the tubing I have, unless it is quite
>sharp; for example, bending the tubing in a "U" that is 1.5" (measured
>at the center of the tubing) across doesn't cause a problem. It has a
>maximum temperature rating of 500 F, so cockpit temperatures won't be a
>problem! The McMaster-Carr label on the bag it came in is says
>
>Vanguard Products
>Size: 3/16" (ID) x 5/16" (OD)
>Material: translucent, 50 Duro silicone
>
>
>Other types might be more prone to collapse, but this one seems quite
>resistant.
>
Well I know to my cost that the standard silicon tubing you can get in
the UK suffers from this problem. Especially if you don't secure the
pipes in the shapes that you want them to follow.

I've also known them to temporarily compress if something moves behind
the panel in severe turbulence.

Robin

--
Robin Birch

[Papa3]

jcarlyle wrote:
> >
> What I'm not sure of is the optimal ID and wall thickness. I picked
> 5/16" OD so they would easily roll over the tubing above, and 3/32"
> width because it would be slightly stronger than 1/16" while still not
> much more expensive. However, a 1/4" OD with a 1/16" width would surely
> hold tighter - but might it distort the tubing to the point of leaking?
> I don't know - opinions?
>
> -John

I'm a big believer in the experimental method :-)) You can pick up a
variety pack of o-rings at most hardware stores (even the so-called
"tools section" at Walmart). I'd try a couple first before buying in
volume. My guess is that 5/16" ID with a thicker wall (ie. width)
would work fine; the barbs on the fitting tend to increase the
effective OD of the tubing, but not so much to cause a problem.

If you're in the US of A, try your local ACE Hardware if you have one.
If it's anything like mine, they actually have a good-ole-fashioned
"hardware" section with bins of O-Rings. I feel kind of sheepish (no
pun intended based on earlier tone of this thread) walking up to the
register with 3 o-rings totalling 15 cents, but hey...

P3

[bagmaker]

Whoa- normal "O" rings? CAUTION! The rubber compounds used in many so-called O rings is not up to the task, UV, Temperature and standard gaseos compounds will break them down in just a few weeks.
If you cant do a test on the ring, like leave it on the cockpit seat for a month or two, stick with a proven thing!

[bumper]

This would be the case for "normal" Buna-N O-rings. It would not apply to
Viton, EPDM "normal" O-rings (g).

If you go into a hardware store and ask for an O-ring, you'll likely get
handed a Buna-N. They do petroleum oils well, but not weather and ozone.
EPDM does DOT brake fluids and resists weather/ozone etc.

bumper

bumper

"bagmaker" > wrote in message
...
>
> Whoa- normal "O" rings? CAUTION! The rubber compounds used in many
> so-called O rings is not up to the task, UV, Temperature and standard
> gaseos compounds will break them down in just a few weeks.
> If you cant do a test on the ring, like leave it on the cockpit seat
> for a month or two, stick with a proven thing!
>
>
> --
> bagmaker

[Doug]

Actually the donuts I've got for my instruments look like the bands used to
castrate male cows and I assume that's what they were originally for. You
can but a big bundle (100's) for cheap. They're easy to use, but just watch
out where you put them ;>)

Doug

"jcarlyle" > wrote in message
oups.com...
> Here's a leak testing article that I found helpful:
> http://www.borgeltinstruments.com/Leaks.pdf
> Sure, it's commercial, but it gives a nice detailed procedure for leak
> testing.
>
> Note paragraphs 3 and 4 near the front. Mike recommends using rubber
> donuts to prevent leaks (I thinking these donuts are similar to the
> grommets used for feeding power cables into metal boxes). He also
> concurs with Doug that cable ties or twisted wire are not good for
> pneumatic systems.
>
> -John
>