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Alt Static Air Source Options

L

lr172

Legacy Member
Had leaks on my previously leak free static system last week. Finally tracked it down to the air switch I put on the panel. It came from Mcmaster, which generally is mid range quality. Seems the orings shrunk over the last few years. Am a bit hesitant to just replace it, but have a 1/2" hole in my panel for it. Any suggestions for a better quality switch or ideas for a better solution? On my 6, I just used a TEE and a cap, but was easy to hide it from view. On the 10, none of the tubing is exposed to the pilot. I was considering a bulkhead fitting with a cap, but is kind of ugly.

Appreciate any ideas
 
lr172 said:
Had leaks on my previously leak free static system last week. Finally tracked it down to the air switch I put on the panel. It came from Mcmaster, which generally is mid range quality. Seems the orings shrunk over the last few years. Am a bit hesitant to just replace it, but have a 1/2" hole in my panel for it. Any suggestions for a better quality switch or ideas for a better solution? On my 6, I just used a TEE and a cap, but was easy to hide it from view. On the 10, none of the tubing is exposed to the pilot. I was considering a bulkhead fitting with a cap, but is kind of ugly.

Appreciate any ideas
Click to expand...
www.steinair.com

Pitot Static Toggle Valve - Steinair Inc.

Pneumatic toggle actuated valve for alternate static air source. You will also need our P-515 fitting to connect to 1/4″ tubing.
www.steinair.com www.steinair.com
 
lr172 said:
Thanks. That looks identical to the one that just failed. Looks like the sam mfr stamping.
Click to expand...
Well now I know where to look first if I develop a static leak. I have the same toggle valve installed. I imagine something like that is difficult to make to where it wouldn't be susceptible to o-ring shrinkage. A bulkhead fitting with a cap is an elegant solution as long as it can be tight enough to seal well and still be loosened by hand when you need it.
 
lr172 said:
Thanks. That looks identical to the one that just failed. Looks like the sam mfr stamping.
Click to expand...
Basically the same switch I have in the SubSonex as a gear switch (pneumatic gear) - hasn’t leaked in six years… but then again, I have a dual air pump to keep pressure up if it leaks! Not like a static system that needs to be very leak free….
 
Ironflight said:
Basically the same switch I have in the SubSonex as a gear switch (pneumatic gear) - hasn’t leaked in six years… but then again, I have a dual air pump to keep pressure up if it leaks! Not like a static system that needs to be very leak free….
Click to expand...
yeah, my leak was not significant, but enough to make the tester unhappy once we got to 5000'. in your case, you probably wouldn't have even sensed the leak as would most pressure applications that use that switch.
 
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lucas2696 said:
Well now I know where to look first if I develop a static leak. I have the same toggle valve installed. I imagine something like that is difficult to make to where it wouldn't be susceptible to o-ring shrinkage. A bulkhead fitting with a cap is an elegant solution as long as it can be tight enough to seal well and still be loosened by hand when you need it.
Click to expand...
i took it apart to see if I could fix it. it has a tiny 1/8-3/16" piston with two tiny orings that do the sealing. Viton orings would probably resolve it over nitrile, but why spend another $.04 when people buy them anyways. i didn't even bother trying to find orings that small.

i can get a nyloseal type bulkhead fitting which should seal well, just not attractive. would definately mak the static tests easier though.
 
Hey Larry- I have the same toggle as you and everybody else, so no help with a better mousetrap in that regard. But it occur to be that for aesthetic purposes if a guy was going to replace it with a bulkhead fitting and a cap, he could epoxy a knurled knob or whatever on the cap to pretty it up and make it easier to turn. You'd get bonus points if you machined a cap out of aluminum, cut pipe threads in it and anodized it danger red.
 
FWIW. Won’t fill the panel hole; but, Mooneys untilized a small 1/4 turn ball valve for many decades. Mine never leaked.

Was mounted to the bottom backside of the panel. Label reference for alt air source with — and | for open/closed. Held in place by an Adel; one end open, the other into a tee in the static line.

No need for a tool to “actuate”, opened easy/fast, still won’t fill a hole in the panel.

Just an option. Take the old one apart and attempt a remedy. What do you have to lose?
 
Check Amazon, there seem to be 1mm thick o rings down to around 1mm ID (that's a bit over 1/32, smaller than 3/64) readily available. Mostly nitrile, but some silicone too.
 
lr172 said:
i took it apart to see if I could fix it. it has a tiny 1/8-3/16" piston with two tiny orings that do the sealing. Viton orings would probably resolve it over nitrile, but why spend another $.04 when people buy them anyways. i didn't even bother trying to find orings that small.

i can get a nyloseal type bulkhead fitting which should seal well, just not attractive. would definately mak the static tests easier though.
Click to expand...
Viton (FKM or fluorocarbon) elastomer has developed an aura of being a "magic" solution to sealing problems in our airplanes, especially as a replacement for nitrile (NBR or Buna-N). Like all elastomers, each is designed for a particular temperature range and chemical resistance.
Here's a comparison source:
www.wyattseal.com

Viton® vs. Nitrile O-rings – Which to Choose? | Wyatt Seal

Choosing Viton® or nitrile O-rings depends on temperature, chemical resistance, and environmental conditions. Learn which material suits your application best.
www.wyattseal.com www.wyattseal.com
I've extracted some data from this source:

TEMPERATURE​

  • NBR: -30°F to 250°F (-35°C to 120°C)
  • FKM: -15°F to 400°F (-26°C to 205°C)

PERFORMANCE CHARACTERISTICS​

  • Chemical Resistance: FKM outperforms NBR in resistance to fuels, oils, solvents, and many aggressive chemicals.
  • Environmental Resistance: FKM maintains integrity under extreme conditions and is resistant to mold, ozone, and weathering.
  • Abrasion and Tear Resistance: Both materials perform well, but NBR typically offers higher abrasion and tear resistance, making it a strong choice for mechanical wear applications.

LIMITATIONS​

NBR O-rings are not ideal for harsh chemical environments or prolonged outdoor exposure. Their resistance to specific liquids can also be reduced when the material is formulated for extreme high or low temperatures. Conversely, FKM O-rings should be avoided in applications involving brake fluid, ketones, hot water, or very low-temperature conditions, where performance may be compromised.

In the limitations of FKM they are referring to automotive brake fluid, not the MIL-H-5606 hydraulic fluid we use in brakes. Viton is used in our wheel brake cylinders due to its high temperature rating, but it does not have as low a temperature rating.

For most of our applications, (except wheel brake cylinders), but including including the switch type alternate static source I think nitrile is a better choice.

Note that ALL o-rings are sensitive to cuts and abrasion when being assembled which is why all parts must be properly deburred prior to assembly.
 
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terrye said:
Viton (FKM or fluorocarbon) elastomer has developed an aura of being a "magic" solution to sealing problems in our airplanes, especially as a replacement for nitrile (NBR or Buna-N). Like all elastomers, each is designed for a particular temperature range and chemical resistance.
Here's a comparison source:
www.wyattseal.com

Viton® vs. Nitrile O-rings – Which to Choose? | Wyatt Seal

Choosing Viton® or nitrile O-rings depends on temperature, chemical resistance, and environmental conditions. Learn which material suits your application best.
www.wyattseal.com www.wyattseal.com
I've extracted some data from this source:

TEMPERATURE​

  • NBR: -30°F to 250°F (-35°C to 120°C)
  • FKM: -15°F to 400°F (-26°C to 205°C)

PERFORMANCE CHARACTERISTICS​

  • Chemical Resistance: FKM outperforms NBR in resistance to fuels, oils, solvents, and many aggressive chemicals.
  • Environmental Resistance: FKM maintains integrity under extreme conditions and is resistant to mold, ozone, and weathering.
  • Abrasion and Tear Resistance: Both materials perform well, but NBR typically offers higher abrasion and tear resistance, making it a strong choice for mechanical wear applications.

LIMITATIONS​

NBR O-rings are not ideal for harsh chemical environments or prolonged outdoor exposure. Their resistance to specific liquids can also be reduced when the material is formulated for extreme high or low temperatures. Conversely, FKM O-rings should be avoided in applications involving brake fluid, ketones, hot water, or very low-temperature conditions, where performance may be compromised.

In the limitations of FKM they are referring to automotive brake fluid, not the MIL-H-5606 hydraulic fluid we use in brakes. Viton is used in our wheel brake cylinders due to its high temperature rating, but it does not have as low a temperature rating.

For most of our applications, (except wheel brake cylinders), but including including the switch type alternate static source I think nitrile is a better choice.

Note that ALL o-rings are sensitive to cuts and abrasion when being assembled which is why all parts must be properly deburred prior to assembly.
Click to expand...
Thanks for the education here. Interesting. One thing not mentioned is shrinkage. From experience, i have seen nitrile rubber orings give up their solvents (a guess here, not sure what is happening chemically) and dry out and shrink over time, at least those not bathed in fluids that prevent it, like atf. Does FKM share the same characteristics? I speculated that it may not, hence my comments. But clearly I don’t know a lot about it.
 
drinkwater said:
Check Amazon, there seem to be 1mm thick o rings down to around 1mm ID (that's a bit over 1/32, smaller than 3/64) readily available. Mostly nitrile, but some silicone too.
Click to expand...
Thanks for the tip. I just broke down and bought another switch from mcmaster. Looks like a different mfr, but similar design. Was only $22. If it lasts another 7 years, i guess that is good value in aviation anyways.
 
$22? That's a wayyy better option than guess-and-chech futzing with mini o rings or trying to measure impossibly small grooves with calipers, or wires, or whatever it would take to pick the right part
 
I like simple so I just dropped a short section of nylo tube down where the vent is and cap it off with some nylo fittings that are easy to reach in flight.
Also doubles as a access point for testing.
 
Walt said:
I like simple so I just dropped a short section of nylo tube down where the vent is and cap it off with some nylo fittings that are easy to reach in flight.
Also doubles as a access point for testing.
Click to expand...
That is what i did on my 6. Simple and effective. On the 10, none of the lines are exposed to pilot. I could run one there, but no real good place to secure it. I really liked the idea of the nyloseal bulk head fitting in the panel and also bought one. In the end i just wanted to keep the panel looking sharp. If this switch fails, the bulkhead fitting is going in.
 
Walt said:
I like simple so I just dropped a short section of nylo tube down where the vent is and cap it off with some nylo fittings that are easy to reach in flight.
Also doubles as a access point for testing.
Click to expand...
I have a question for which you are well qualified to answer. While my static is now leak free again, we also found a leak in the Pitot. I can’t get to the fittings without dropping the pitot. The stupid gretz has threaded inserts embedded in the compsite and one spun on me, so a big pita now to get it out. If i pull a 10” vacuum on that line to the pitot, it will drop to 0 in about 5-7 seconds. A decent leak but not huge. Always figured the pitot system is pretty tolerant of leaks. Do you believe mine is enough to cause inaccuracies? It used to be leak free and my speeds seem very consistent to what they used to be.
 
lr172 said:
I did. It ha two of the tiniest orings i have ever seen. Have no idea how i would order replacements.
Click to expand...
For future reference, this has been a reliable source for NBR and FKM orings in *lots* of sizes for me:

Orings and More | Metric Orings and Hydraulic Seals

Stocking distributor of metric o-rings and seals in various materials and sizes. Metric Orings in Buna 70 & 90, Silicone, Viton and EPDM material.
oringsandmore.com oringsandmore.com
 
lr172 said:
I have a question for which you are well qualified to answer. While my static is now leak free again, we also found a leak in the Pitot. I can’t get to the fittings without dropping the pitot. The stupid gretz has threaded inserts embedded in the compsite and one spun on me, so a big pita now to get it out. If i pull a 10” vacuum on that line to the pitot, it will drop to 0 in about 5-7 seconds. A decent leak but not huge. Always figured the pitot system is pretty tolerant of leaks. Do you believe mine is enough to cause inaccuracies? It used to be leak free and my speeds seem very consistent to what they used to be.
Click to expand...
From my experience small leakage in pitot is not something to worry about. There is an unlimited amount of air to compensate for the leakage.
 
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Walt said:
From my experience small leakage in pitot is not something to worry about. There is an unlimited amount of air to compensate for the leakage.
Click to expand...
thats what i thought. Thanks for the help. I believe the static guy ties the pitot and static together during the testing, so he will still have to deal with the leakage during testing, correct?
 
For reference, the Cessna (heated) pitot head has a small hole drilled in the bottom aft corner of the casting as a water drain (when flying through precip). During one of my pitot static checks on my C-150, the tech neglected to tape over this hole and of course, the test gear showed a massive leakdown. Taping over the hole brought the test gear back to an acceptable level and my system passed the test.

If you know the pitot head has a known leak (water drain hole or otherwise) make sure the tech tapes over the hole/leak and you should be fine.
 
terrye said:
For reference, the Cessna (heated) pitot head has a small hole drilled in the bottom aft corner of the casting as a water drain (when flying through precip). During one of my pitot static checks on my C-150, the tech neglected to tape over this hole and of course, the test gear showed a massive leakdown. Taping over the hole brought the test gear back to an acceptable level and my system passed the test.

If you know the pitot head has a known leak (water drain hole or otherwise) make sure the tech tapes over the hole/leak and you should be fine.
Click to expand...
Every heated pitot has a drain hole, I can't imagine a repair station that does these checks didn't know this.
 
Walt said:
Every heated pitot has a drain hole, I can't imagine a repair station that does these checks didn't know this.
Click to expand...
yes, tester knows that. however, the gretz is unique and does not have a drain hole like all the others. At least that is what the internet says. previous certs we did not plug any drain holes and it held a vac quite well without leaks. something changed in the last two years.
 
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