What are the best static connectors? How to locate static system leaks?
- Thread starter FORANE
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My 210 is undergoing an avionics upgrade currently and it was discovered that the tubing and connectors behind the panel are all PE tubing with Steinair (supplied, anyway) pushlock connectors. My avionics tech doesn’t like them but they have been functioning, leak free, since 2015. He kept that system and added on to it for the additional GI275. I understand that if the tubing is cut properly (square cut sharply), pushlock connectors are reliable. Supposedly, Steinair supplies the best quality.
I use only Swagelok nylon connectors and fittings. However, most similar type nylon connectors can work just as good.
You just need to be able to pull a controlled vacuum. Any hand operated vacuum tester like used for vehicle systems will work. Or if you feel adventurous, a large syringe can work if you hold your mouth right.
Ed Haywood
Final Approach
Push-to-connects work great.
I have push connectors. The tech said they are leaking. I read they are better in positive pressure applications.
ok, pull a vacuum but how to locate the leak? On vehicles evap I have a smoker but what I find works better is a small positive pressure then soapy bubbles on all lines. We can't use small positive pressure in the static system can we?
The altimeter can safely indicate -1000ft. That's an extra inHg of pressure, or about half a psi. Enough to see bubbles if you have a leak.
Personally I prefer and only use Nyloseal fittings. They take nominally longer to install/remove than the push-on connectors, but they seal nicely and are otherwise very easy to work with. Tons of stories online of push-to-connect fittings leaking, etc. And based on what I've seen, most shops don't use push-on connectors and use some variation of Nyloseal/polyflo instead.
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Ed Haywood
Final Approach
Could be cheap connectors. Or wrong type tubing. I got good results with firm Polyurethane tubing. IMO nylon is too stiff for these type connectors.
I buy my connectors and tubing from McMaster-Carr. https://www.mcmaster.com/catalog/131/166/5648K69
I don't like the brass poly-flo connectors, I think they're just harder to use (they're knurled, rather than really setup for a wrench).
I've re-plumbled several airplanes w/ nyloseal fittings. It's critical that the tubing is cut very straight, and you have to use the little inserts (without those, they will leak).
Ed Haywood
Final Approach
That's what got me started on the PTC. When I refurbed my aircraft, I redid everything in PTC. Previously it was hard aluminum tubing.
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Mainly trial and error. Once you block off your static ports(s) and connect the vacuum pump to the system, pump it to 1000' and see how fast it leaks. Note: if you want to go above 1000' you'll need to disconnect the airspeed indicator static line and cap it, then you can go higher. If it leaks down right away or you can't get a vacuum to hold, perform a visual and tactile check of all the lines, etc. for something obvious. If you can hold a vacuum, perform a "wiggle" check of the lines, etc. to see if it affects anything. If none of that works, then you'll need to split the system at a convenient place and chase the leak(s).
In general, no. But, there are times when it can be necessary. However, you must disconnect all indicators and devices and cap the lines. Then you can add pressure and use leak check or soap to chase the bubbles. Regardless, I would only use that method with larger aircraft or a complex static system with limit access. The above-mentioned process works for 95% of the static leaks once you get used to it.
Nyloseal are similar to the nylon Swageloks I use and are a good option and have used them as well. Not a fan of the push connectors or metal/nylon fittings. For a bullet proof static system the go to is AN fittings and Aeroquip 306 rubber hose. However, it is bulky, weighs a bit more, and can cause other install issues.
MauleSkinner
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Is that probably how the guy busted both my airspeed indicators doing a static check?
Dan Thomas
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Most pilots have little idea how sensitive static instruments are. One has to be really careful in applying suction to the system. Watch that VSI closely; it will peg out almost instantly if you're in the tiniest bit of a hurry, and you could damage the aneroid in it. Let the suction off slowly, too.
An inch of vacuum gives you a 1000-foot rise, and it makes the ASI read 162 MPH. You don't want to peg that ASI either.
Cessna has used Nyloseal for decades, and it works well. Most of the leaks I've found are due to negligence on the part of the last installer, or to age. The little plastic condensation trap at the static port is famous for cracking at the threaded bosses, and I have also found them installed with no sealant on the threads. Found them distorted by heat from the heater vent just below that trap. They're behind the kick panels, and people (and mechanics) can sometimes put pressure on them while struggling into or out of the airplane. Much of the time I fixed leaks by just snugging up every tubing nut in the system, occasionally taking out a fitting from an instrument and applying sealant to the threads. I didn't need to put positive pressure into anything. Don't overlook the line to the encoder.
Main advantage for me (as an owner/amateur mechanic) is that Nyloseal requires basically no special tools at all. Easy to fabricate, easy to repair, easy to shorten, easy to just totally re-run, and no specialty tools are needed (I do have a hose cutter, but the tubing can be cut with a single razorblade if you're careful/precise). Making real Aeroquip hoses w/ AN fittings is a very different exercise requiring different skills and tools (and cost).
Maybe. However, most shop level test equipment that test static and pitot systems at same time usually have a crossfeed adjustment that allows to manage static altitude vs exceeding the airspeed limits. Now if he failed to operate the crossfeed properly that could allow the airspeed to pegged out. Or he could have dumped system pressure which I've found can damage an ASI as well.
Nyloseal and the Swaglok nylon fittings I've used are basically the same. I just preferred the Swage build quality and they seemed to adapt to a larger variety of poly/nylon tube brands. However, at my Part 135 day job we used Nylo fittings were possible with the rest being OEM spec'd AN-306 hose systems.
Not aware of any special tools or different skills required to install AN 471 fitting to low pressure 306 rubber hose? But definitely more cost. However, there are still some of these lines I fabricated 35+ years ago that are still going strong.
Let'sgoflying!
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Specifically, disconnect the blind encoder before testing.
Do the AN471 fittings not require a mandrel, vice, etc.? I've seen my A&P fabricate a few; for an "amateur," it appeared more involved then snipping the nylon hose, putting in the insert and off to the races.
No. You're thinking of 491 fittings and 303 hose. Its the hose type that drives the need for mandrels. With the 471/306 combo you simply use an AN806 plug to lock the B-nut on the flare nipple and push it into the hose with the hose socket installed. Usually done by hand with a couple wrenches if needed. Not much real difference overall between this and using nylon fitting and tubing which both have their own pros/cons.
Silvaire
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Basic troubleshooting - split the system and see which half has the leak, rinse and repeat until you nail the culprit.
Let'sgoflying!
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so easy to put some things into words, so difficult to actually enact!
Sure, but I don't have the equipment to pull a tiny vacuum safely. What equipment is available to the non-pro to perform this troubleshooting?
Silvaire
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Thanks for that. I really don't want to have a maintenance induced failure...
Ed Haywood
Final Approach
Several pump/gauges on Amazon for 20 bucks.
Just go slow. However, a syringe will only work on systems with no leak or a very small leak. I kept an old metal version of the hand-pump linked in post 6 in my toolbox for years for just that type of work.