air compressor

[canderson]

Hello,

The TCM inspection bulletin (SB03-3) for a cylinder differential pressure test states the compressor should be able to deliver 125 psi with a minimum of 15 cfpm to succesfully run said test. When I look at the availability and cost of machines with these specs, which seem to require 220V in most cases, the prices seem pretty darn high, besides the fact that the 220V requirement is, to me, prohibitive in and of itself.
I'd like to hear what people have for compressors that allow for compression tests and other 'normal' activities such as riveting, painting, tire inflation etc...

Thanks

ps. made it to my first Sun n Fun this year commercially, and it was a blast. Oshkosh is next, after convention hopefully.

[bsdunek]

The only recommendation for air supply for compression testing I could find had the same requirements, 125 psi @ 15 cfm. Eastern's E2M tester requires a minimum of 90 psi, so I'm not sure of the 125 psi. Witha 0.040 orifice, probably 15 cfm would be a good number to look for. Sears sells an Ingersol Rand 5 HP compressor that is rated at 14.8 cfm at 90 psi, so it looks like a 5 Hp compressor might be an absolute minimum. For 5 HP, you certainly want to run it on 230 VAC, which you probably don't have in your hanger - I sure don't.
For the other tasks you mention, riviting, painting, tire inflation, etc. a one HP compressor is adequate. I have an old Sears one HP two cylinder that will run a small spray gun just fine. Riviting is not a continous use, so the compressor doesn't have to keep up with the gun, just average out. Tire inflation takes nothing at all - witness the cheap Chinese 12 VDC units they sell at the auto parts.
A one HP unit just gets buy on a 20 Amp 120 VAC outlet.
I let my shop do the compression testing, although it would be nice to check things out once in a while.

[Watkinsnv]

I would think that any air source that can maintain the inlet pressure on the gauge during the cylinder test would work. Lance

[lowNslow]

I have a five HP compressor 120volt which keeps tripping the CB in my hangar, so I sometimes borrow my neighbors 2HP small compressor and it works just fine for compression checks. Unless you have very leaking cylinders you really don't need a big compressor.

[Bruce Fenstermacher]

I have a small 2 gallon compressor, probably one horse I got as a bundle with some air nail guns at Home Depot. I use it for filling tires, painting small pieces or touch ups, riveting and compression checks.

I would not plan to use it to paint an entire airplane. It does fine for compression checks on our size engines but might not on larger cubic inch engines.

It runs on 120 doesn't draw much current, easy to move and will fit in your trunk.

When I'm at the hanger in the next day or so I'll try to remember to write down the exact make and model number.

[blueldr]

In a word or two:

You don't need that much compressor for that job.

[Jimmy M.]

I've got a friend that rigged up a compression tester with a scuba tank.I've used it and it works well.Easy to hear any leakage with no background noise.
Don't know how many tests he can do with one fillup.

[canderson]

Well, I wasn't sure but I sort of suspected those numbers were on the high side, especially for our smaller engines as you said Bruce.
Thanks for all the advice. I think I can confidently choose something now and not have to sell the plane to afford it!

[jrenwick]

There are two kinds of compression tests now -- the old way, where we're happy if the cylinder can hold at least 60 out of 80 pounds (or higher than 60, if you wish), and the new TCM procedure, which requires comparing the cylinder's leakage against a standard orifice. The latter test is really about establishing a standard for ring leakage, below which TCM is willing to honor its warranty on new cylinders. It requires that the reference pressure be kept constant against leakage down to 40 PSI, and it may indeed require a 5HP compressor to do that.

Clearly the leakage tests we're used to doing don't require that high a flow rate, but if it comes right down to whether or not TCM will replace a cylinder on warranty because of leakage past the rings, you might have to certify that the test was done with a compressor that met their spec.

Disclaimer: this is my guess on this subject. I'm not a mechanic, but I've listened to our local expert, Daryl Bolduc, lecture on the subject. He didn't say this exactly, but I believe it follows from some things he did say.

Best Regards,

John

[blueldr]

I can't see where the engine size would have anything to do with the required compressor output volume. The air has to go through a sized orifice at a given input pressure which is the same for all engines. It appears to me that any compressor able to maintain the required constant input pressure should be adequate.

[Bruce Fenstermacher]

BL

I was thinking about the smaller compressors and the reservoir they have. The compressor itself may be inadequate but the reservoir may have enough volume for smaller cylinders to accomplish the task.

[Watkinsnv]

Whan I did my remote prebuy annual inspection in Elko NV. I used one of those air tanks that they have to fill tires. I got three cylinders on the charge that I had and asked to fill the tank at the Elko FBO, and then got the other three cylinders. Lance

[Bruce Fenstermacher]

Here is the compressor I bought at Home Depot and use for my compression tests as well as bucking rivets and nearly everything else.

It has a max psi of 135psi and rated at 2.6 scfm@90PSI. 2HP with a 6 gallon tank. made by Porter Cable.

0427081237a.jpg (144.41 KiB) Viewed 8213 times

[GAHorn]

135 psi? Made my Porter-Cable, heh? Thanks.
What color is it?

Seriously... what does a small compressor like that sell for? That looks like something a travelling mech. might find pretty useful.

On a somewhat related matter.... I had to buy a new car this month and the dealer offered to do me a special favor and fill my tires with Nitrogen for only $100.

Much better for tires he said. They'd last much longer and keep pressures better than air... it's so good that's what they use on airplanes, ... etc etc.

I bought a "Q" cylinder of Nitrogen for our Hawkers/King Air's when we operated at remote airports, etc. Whenever we needed it refilled (which was only twice in about 5 years, having to service 3 airplanes with 15 tires regularly with it) the refill cost $11. At that rate, I think there might be a wee bit of profit in the dealership's tire-inflation scheme, perhaps.
Whaddya think? (I didn't have the heart to remind him that about 80% of whatever the shops air compressor delivered into a tire was .... Nitrogen!)

[Bruce Fenstermacher]

George,

I was in the market to buy at least one pneumatic nail gun. In reality I needed two because I wanted to drive both small brads and larger ones the small nailer couldn't shoot. I mauled over the purchase for hours at the Home Depot even went to my favorite ACE to compare. Back at Home Depot a salesman stopped an said they had a deal going. Two nail guns and an air compressor. I didn't want the air compressor thinking it waste of time plus I already had a large air compressor and enough hose to reach around by house.

The salesman said considering I needed two size nail guns if I bought the bundle the compressor was free and plus it came with a hose and couplers worth another $30.

I bought the bundle and love the air compressor. In fact i wish I had two of them. Yes I can put it in the trunk of my Honda and I use it like an air bottle when I need air at a remove location.

I seem to remember the total deal, 2 guns, air compressor, hose and couplings to be in the $300 range. It's turned out to be a pretty good purchase.