Nitrogen rig question

[icefr8dawg]

I need to replace my friends strut coupler on his nitrogen service setup. I filled his tank but found that the coupler/air chuck that attaches to the airplane's strut was run over in the shop somehow. I did find one coupler on aircraft consumables but it dosn't have a center pin to depress the strut's schrader valve. It's the 70 degree screw on type and looked just like the one I'm replacing and have since thrown away...
How does the air get into the strut if the valve isn't depressed? Am I missing something here or did I order the wrong part?

 

[avbug]

A schraeder valve is different than a tire valve; it requires a wrench to open the valve, and this should be done once the fitting is attached to the valve stem. Once the pressure line and fitting are attached, the valve is opened with an open end wrench. Then apply the requisite pressure, very, very carefully. Close the valve with the wrench, then shut off the nitrogen supply pressure. That done, very carefully slightly loosen the attach fitting on the pressure line from the nitrogen bottle, allow the pressure to bleed out of the line, and once it's bled off, remove the fitting.

Be careful, because you'll think you haven't got enough pressure in a strut or compression unit, and in fact you may have too much; it's sticking. Throwing too much nitrogen to any component is a good way to get hurt, so use caution and adhere to the manufacturer's procedures exactly.

 

[bocefus]

I'd modify that procedure somewhat so as to avoid contaminating the GN2 system. Most shops use the same bottle, reg and line to pressurize tires, and others systems.

 

[icefr8dawg]

Thanks guys. I remembered something about a nut having to be opened but haven't done struts in a long time. It's on an aztec so I have to see what type of valve it has and probably replace the wear items.

 

[Torqued]

Many light aircraft use a filler valve on the strut that's almost identical to a tire valve. The tire valve type can be opened by pressure from the servicing bottle without depressing the valve core pin. The problem is that the servicing pressure has to exceed the internal pressure by up to a couple hundred PSI. This is no problem if the nitrogen bottle is full but you have to be carefull and use a valve that has quick and accurate control of the nitrogen. The pressure required to open the tire valve type can vary quite a bit between individual valves.

 

[icefr8dawg]

That's what the guys at my real (jet) job said today. I guess that makes sense. I looked at the valve and it is indeed the tire type and not the high pressure with the nut type. The maintenance manual talks about using shop air but i'd rather do it with N2 and not worry about it for a couple of years.

 

[erj-145mech]

An aircraft owner may perform preventive maintenance, which includes servicing struts (FAR 43 Appendix A (c)(3), but that does not give you the authority to deviate from the manufacturers maintenance manual. You must also release the aircraft for service after you perform any maintenance (43.9).

 

[wooferdog]

icefr8dawg-

Tronair has those. www.tronair.com

-wd

 

[icefr8dawg]

ERJ I'm pretty sure Piper is ok with using Nitrogen instead of shop air even though they dont mention it in the manual. Deviation yes, but I'd equate it to replacing a damaged galvanized firewall with a better stainless alloy, no?

 

[avbug]

Deviation yes, but I'd equate it to replacing a damaged galvanized firewall with a better stainless alloy, no?

Not a good equation. When you replace a part or fabricate a patch, or repair something, you use the same material, or something approved of the same strength. You don't build it bigger, stronger, better. What you end up with is an entirely new set of dynamics with respect to strength, and increasing strength in a part puts stress on other areas adjacent to the part...you can cause more damage than you'll help. To say nothing of dissimiliar metal issues and the increased potential for corrosion.

So far as putting nitrogen in a strut, you're not going to hurt anything, but don't buy into the idea that bigger molecules mean less frequent service, or any of the other garbage you'll hear about why nitrogen is used. It's more stable, contains and supports less moisture of condensation, and doesn't support combustion and oxidation as an oxygen atmosphere does.

You will not go wrong adhering to manufacturer recommendations and maintenance publications.

 

[icefr8dawg]

not bigger or stronger just smarter. I don't know what piper was thinking using cheap thin galvanized metal in a hot exhsust area... Stainless was the fsdo's idea

 

[avbug]

Not necessarily smarter.

The manufacturer can approve material substitutions, whereas the FSDO can't.

Field approvals are not a local approval any more, either.

Remember that a patch made of dissimiliar metals means corrosion, to say nothing of strength, and in some cases with proximities of different coatings and materials, embritlement and other issues, too.

While a change to a commonly used firewall material like Stainlessmight sound smarter, it's not necessarily so.

 

[icefr8dawg]

I suppose one could have fixed the problem with $20.00 of NAPA exhaust wrap fifteen years ago but, oops, that's almost 100% non pma isn't it?
These planes just weren't made to last the way we've demanded.

 

[avbug]

PMA isn't really relevant. The airplanes were made to last indefinitely, so long as they're maintained.

 

[icefr8dawg]

Perhaps made to last forever with a total and complete teardown every now and then. My point was they, Piper and Cessna really messed up in the old days when they chose inferior materials in certain areas. 1960's and 70's mostly.
And my J-3 has a 4130 repair where it had good old 1943 mild steel, no engineering or stress analysis, just "better" and there isn't a fed that would fault me for welding it in that way. Most couldn't light a gas torch without blowing themselves up for that matter.