Compressed Oleo

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MSUDavid

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MSUDavid
71C85371-4738-487F-8C2E-896071554061.jpeg 71C85371-4738-487F-8C2E-896071554061.jpeg I went to the hangar yesterday for a quick flight since the weather is getting nicer. Wouldn’t ya know one of my main pleas was flat on the Archer. I have no good maintenance on field, so I was searching for options to air it up. There was no 5606 leaking, so I knew it had to be low on Nitrogen.

This one had been leaking slowly anyway, and at last annual we added some Grandin strut seal. Apparently that didn’t work and I need a rebuild kit. I needed it aired up to get it to my A&P. Searched Spruce and the cheapest strut pump was over $300. Not crazy in aviation terms but kind of high for something you never intend to use. Called A&P and he recommended that I buy a mountain bike shock pump. It cost $30 and worked! Just thought I would share to save someone a few bucks. It is also small enough that I am going to add it to the items that ride in the baggage compartment in case of emergency.
 
Interesting. I have one of those pumps. Will have to check the psi range.
 
Jdm said:
Interesting. I have one of those pumps. Will have to check the psi range.
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The one I bought says it is rated to 300 PSI. The guage went to 400. I didn’t have anyone to lift the wing, so I would pump up to 290 and then go lift the wing. It might go up 1/4 inch and then repeat because the guage was back down to 220. It would have been much easier with someone there. It did take a lot of pumping though, but not excessive.
 
Most use an aluminum gasket. DO NOT reuse once disturbed. Cheap.

A jack would help. Possibly some weight on opposite wing tip would help.​
 
MSUDavid said:
This one had been leaking slowly anyway, and at last annual we added some Grandin strut seal. Apparently that didn’t work and I need a rebuild kit.
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Just rebuild it for crying out loud. The kit is literally a few bucks on Spruce and can be done in a few hours with a competent mechanic. Granville at this point is putting a band-aid on a bruise.

You probably have an upper air leak if I had to guess. The Granville will help soften up seeping lower seals, but if they’re old and worn out, which I’m guessing they are, they need to just be replaced, else you’ll be fighting this problem repeatedly. Adding the Granville during or right after the rebuild is the best time.
 
This is not unusual in cold weather. Regular 5606 has no seal conditioners...the Granville strut seal will often help if the seals are not shot. Strut pumps work ok, but I prefer to extend the strut with the plane on the jacks and use "dry compressed air " from an inexpensive 14 volt compressor on my Bonanza. About 160 psi for the mains and 110-120 psi is about right on the nose strut. The compressor I use has its own gage, and no storage tank to collect moisture. Whenever I reach desired pressure, I simply disconnect at the strut. Be sure the shrader valve seals properly. Replacing the shrader valve is very inexpensive fix.
 
RyanB said:
Just rebuild it for crying out loud. The kit is literally a few bucks on Spruce and can be done in a few hours with a competent mechanic. Granville at this point is putting a band-aid on a bruise.

You probably have an upper air leak if I had to guess. The Granville will help soften up seeping lower seals, but if they’re old and worn out, which I’m guessing they are, they need to just be replaced, else you’ll be fighting this problem repeatedly. Adding the Granville during or right after the rebuild is the best time.
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I don’t disagree with the rebuild. I have never added any N since I bought it except for this last annual in November when we added the Granville. Worth a shot for an easy fix. Didn’t work so a rebuild is needed. I just wanted to share an inexpensive way to expand the oleo to get it to maintenance not on the field.
 
Magman said:
Most use an aluminum gasket. DO NOT reuse once disturbed. Cheap.

A jack would help. Possibly some weight on opposite wing tip would help.​
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Good advice. I’ll make sure to not reuse it.
 
I stopped using shop air in struts a long time ago! Nitrogen is much better to keep in a strut.
I will say, I never thought about using this little shock pump to get the job done in a pinch. Would be perfect for remote location until I can get home to repair and service properly. This one goes up to 300psi and is very small.
 

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Jdm said:
I stopped using shop air in struts a long time ago! Nitrogen is much better to keep in a strut.
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Agree. Nitrogen is best as it doesn’t have any moisture in it, unlike shop air, that can corrode the strut. It’s surprising how much moisture ordinary shop air holds.
 
Thanks for the suggestion about the pump. It sounds like a useful thing to have.
 
RyanB said:
Agree. Nitrogen is best as it doesn’t have any moisture in it, unlike shop air, that can corrode the strut. It’s surprising how much moisture ordinary shop air holds.
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Exactly why I stopped using it! Most flight schools and even shops will use air because it’s so convenient. Unfortunately I picked up on this poor habit and continued taking the short cut until I saw the damage in comparison to struts filled wit N2. It was significant.
 
Air vs. Nitrogen is a religious argument, I'll not weigh-in on.

However, this is the bicycle strut pump I keep in my Warrior. Rated to 600 psi.
https://www.amazon.com/gp/product/B00D0SFMJS/

Bought it just after rebuilding the nose strut, and have not yet needed it.
 
Capt. Geoffrey Thorpe said:
So all the condensed water goes straight into the strut instead of collecting in the tank?
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Yes, I was thinking the same thing actually. Either way there’s still moisture regardless. Here’s a pick (after cleaning) of a strut serviced for years with shop air.
 

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So if moisture and greater permeability leakage of air is the problem, is it outlandishly expensive to get a bottle of nitrogen. And if you had it, Is there any input port on these strut pumps to allow hookup to said bottle. (Of course only if you are trying to eliminate any air/moisture contamination temporarily in the strut.)

I realize it is all available and easily done by your A&P, but in this case, not on the OPs field.
 
MajorTurbulence said:
is it outlandishly expensive to get a bottle of nitrogen. And if you had it, Is there any input port on these strut pumps to allow hookup to said bottle.
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For comparison...the cost of nitrogen and the bottle varies a bit but usually you can get a filled bottle for less than $100 at a HVAC or welding shop. My 5 foot steel K (?) type bottle costs about $50 to refill and would last over a year usually. But I was using it a lot then. The gauge set/hose/fittings were less than $200 but there are cheaper options if so inclined. As to the strut pump never needed one on small aircraft with a bottle at least half full. If the bottle pressure was below 500psi or it was a heavier aircraft might need the pump but I had a surplus pump I rebuilt for $50.
 
I could use a small nitrogen set up myself. It’d be a lot easier than borrowing from the shop or my corporate outfit. Anyone have a reference for decent quality, reasonably priced gauge and regular setup please advise.
 
Jdm said:
I could use a small nitrogen set up myself. It’d be a lot easier than borrowing from the shop or my corporate outfit. Anyone have a reference for decent quality, reasonably priced gauge and regular setup please advise.
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I am in the hi pressure cly business. We refill some gases and send tanks out to be hydrotested. I have many aluminum and steel tanks that I swap valves in for different types of gases over the years.

Find a place that does hydrotesting and see if you can buy a tank from them. If they can't sell you a valve or regulator then get one from a welding supply. A argon regulator is what you use for nitrogen. I make my own hoses and use steel chucks that I use on big trucks to charge my strut. There are screw on chucks also that are handy for precision filling.
I refill my small tanks from a large tank with trans fill hoses.

I suggest not to mention aircraft when looking for a tank. Tell them you want to recharge shock absorbors.
 
Thanks Gary. Excellent information. I’ve never used anything other then the screw on type chucks for nitrogen. Makes it easier for one person.
 
MSUDavid said:
I don’t disagree with the rebuild. I have never added any N since I bought it except for this last annual in November when we added the Granville. Worth a shot for an easy fix. Didn’t work so a rebuild is needed. I just wanted to share an inexpensive way to expand the oleo to get it to maintenance not on the field.
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If there are no fluid leaks, you don't need a complete reseal job. The nitrogen charge is leaking out via the Schrader valve or the valve body. The nitrogen charge sits on top of the fluid. Pipers are known for this.

Get new aluminum washers and 'H' rated Schrader valves. Remove body and clean where washer contacts strut top. Reinstall body with new washer and valve.
 
JAWS said:
If there are no fluid leaks, you don't need a complete reseal job. The nitrogen charge is leaking out via the Schrader valve or the valve body. The nitrogen charge sits on top of the fluid. Pipers are known for this.

Get new aluminum washers and 'H' rated Schrader valves. Remove body and clean where washer contacts strut top. Reinstall body with new washer and valve.
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This is exactly what happened. I sprayed some soapy water on the valve and had some really slow bubbling. I picked up a schrader valve tool from Napa, and I was able to snug it up (about 1/3 of a turn) without overdoing it. Sprayed more soapy water and didn’t have any bubbles.

I am learning something new about maintenance everyday!
 
Thanks! That’s a great website. Definitely want to build at setup soon.
 
Capt. Geoffrey Thorpe said:
Every shop has air with close to 100% humidity out of their compressor because the water beyond that collects in the tank.
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It will depend on the tank temperature. If the air is allowed to sit in the tank and reach ambient pressure, much of the water will condense in the tank. Run that compressor for a long time, using air tools or spray painting, and the tank can't condense it so that much of the vapor travels on through and out of the tool or spray gun, often condensing there due to the large pressure and temperature drop. You get more water coming out the tool's exhaust, or causing cratering in the paint.

My long experience, long ago, with air brake systems used in heavy trucks and earthmoving equipment showed the damage water can do. It rusts out tanks. It washes lubricants out of control valves and causes corrosion in them. It freezes them solid in in cold weather, making the system unreliable. Two ways were developed to deal with it: finned tanks to cool the air and condense the water and automatic valves to eject it. Didn't work well at all in warm, humid environments. Dessicant filters took the compressed air from the compressor and absorbed almost all the water out of it, with an air blast to drive the water off the dessicant beads and out when the compressor unloaded. Worked far better. You'll hear that thing blast off sometimes when you're driving alongside a big truck on the highway.

In large industrial shops, the compressed air is refrigerated, the condensed water extracted, and the air returned to ambient temps.

Nitrogen makes much more sense for strut servicing.
 
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