New Compressor - Very Slow Leak / Normal?

[buckeye95]

All,

I just purchased a Porter Cable C1010 1-gallon oil-free compressor and broke it in yesterday by running it for 15 minutes with the drain open (per the instructions). All I can say is wow. Though small, it is not only light (24 pounds) but the quietest compressor i have ever used. I was looking for something for those small "punch out" jobs around the house that could avoid lugging it's 60-pound big brother around, and this seems perfect.

Unfortunately, after firing it up with the tank drain closed, it seems to have a very slow leak. Was up to 135 psi last night after cutoff, and dropped slowly last night down to 60 psi this morning. I checked and the drain valve is tight, and unfortunately i think the leak is so slow it would be nearly impossible to find with the soap-and-bubbles method.

Is this normal for most compressors? I just got it and could return it for a replacement, but don't want to hassle with it if this is just the way that compressors are in terms of holding air long term.

Regards,

Pete

[unknown poster]

My compressor will hold pressure if the drain and regulator are closed. If the regulator is open I get a slow leak, probably from one of the connections or the quick release adaptor.

[sweensdv]

Both of my compressors have slow leaks like you described, even when the pressure regulator closed. The common denominator on both compressors are quick connect couplings so that is where I believe the problem lies. All my fittings have been purchased at either HD or HF so that could also factor into why they leak.

[cwsmith]

Quick answer: YES!

Most all of the fittings in the assembly or the compressor are threaded and/or with some "compression" fittings. Too little or too tight and they leak and, too little pipe dope they leak. Quick connect final fittings leak notoriously.

Challenge of course is to find where the leak or leaks are at. Usually it's an easy fix.

I have two Craftsman compressors, my larger 33-gallon, 150 psi oil-less leaks about 10 psi over a course of about two to three hours... thus I cannot ever just leave it in the ON position (not that I would anyway).

My little 2-gal, 125 psi lube unit doesn't leak anything noticeable and I've actually pumped it up and left it that way and weeks later it will have lost maybe 5 psi, if that.

So YES, I would say it is quite normal. If it is to the extend that it is annoying, get some "bubble soap" and start checking the conections.

CWS

[LCHIEN]

Lets apply a bit of engineer thinking to this:

a quick point, with only 1 gallon accumulator tank, any leak will manifest itself as a faster loss of pressure than with a bigger tank. For example, if your other compressor is a 10 gallon tank, the same sized leak would have only dropped the pressure 7 PSI instead of 70 psi. Perhaps your expectations were set too high?

another way of looking at this:
135 psi ~=9 Atm
60 psi~=4 Atm
so you lost 5 Atm. x 1 gal = 5 Standard gallons (at normal pressure.) = .65 Standard Cu ft.

Assuming it was over a period of 12 hours (you weren't specific) or 720 minutes,
then the size of your leak is approx .001 SCFM (that's 1/1000th of a Standard cubic foot of air per minute, standard meaning at normal or room pressure). A few hours more or less still gives us an order of magnitude for the leak, order of magnitude meaning 1, 1/10th, 1/100th, or 1/1000th or basically how many decimal points).

This is essentially nothing where the order of magnitude of SCFM flow for tools and compressors is 1 SCFM. Its of no importance other than if you want to have a perfect system or leave it on all the time and not have it cycle.

Finally, if you do want to make it perfect, I think some soapy water would find the leak easily. .001 SCFM would blow 250 .5" diameter bubbles per minute. Or around four bubbles per second.

FWIW, I'm not expecting my compressor to hold pressure for a day without losing any pressure, esp. with a hose attached. Quick coonnect fittings would be a prime candidate for leaks, first off.

[Daryl]

Probably don't apply here, but if the tank was hot when you pumped it up, such as running for a long time, then when it cools, the pressure will be less.

[cwsmith]

Thanks Loring,

I'm always impressed with your "engineering" and very well-expressed, and easily understood explanations.

[LCHIEN]

Probably don't apply here, but if the tank was hot when you pumped it up, such as running for a long time, then when it cools, the pressure will be less.

That's true but a minor effect. THe ratio of pressure vs temperature is based on an absolute temperature scale such as Kelvin.
Suppose the tank went to 70 C which is about 160F and
way too hot to touch - you'd really notice that. I doubt it got anywhere near that hot. Room temperature is 25 C (77F). Converting to an absolute Temperature scale of Kelvin which is 273 degrees + the Centigrade temperaure,
the cold tank would be 273+25 = 295K and the hot tank would be 273+70C=343K.

SO the temperature reduction as the tank cooled from 160F to 77F would be Press_cold=Press_hot x 295/343 = which is a reduction of about 16%. THat would take a 135 psi tank to 116 psi. In reality, I doubt the tank got anywhere near 160F, so the pressure drop due to temperature change would be much, much less than 20 psi.


P.S. just measured my compressor - 8 Gallon Pancake Oilless. Emptied it, let it fill the tank to shutoff. Tank temperature rose from 80F to 88F -indicating the air inside was probably heated some and the equilibrium of the air and the metal tank was 88F. CHange was 8F or 4.44C So when it cools back to 80F (that's the temp in my garage tonight) it will pressure will change by -4.4deg/300 or -1.4% which is a drop from 130 PSI to 128 PSI.

[LCHIEN]

I had some QC fittings audibly leaking, I blamed it on HF QCs - I have bought several of the five piece for $3.99 I think 1 QC females and 4 studs http://www.harborfreight.com/5-piece...set-68237.html

AFter doing a bunch of mixing and matching, it turned out the HF stuff was fine, the Husky fittings I had from HD were leaking. Took them back and exchanged for another set and they worked fine.

[cabinetman]

Slow leaks are normal. You could do a soap and water check, which is the simplest method. I've had slow to very slow leaks in small systems to large ones. Even on my IR 80 gal tank with a ball valve shutoff at the air discharge.

.

[buckeye95]

Thanks for everyone's comments. Looks like this is just the way compressor systems go.

Regards,

Pete

[LCHIEN]

you could improve it by looking with soapy water and fixing the leaky points, but I don't think its necessary.

[cabinetman]

Many leaks can be minimized by some prudent parts assembly. I like using Teflon tape. Some of the mating threads may have some burs so, screwing the mating parts together dry first may clear out some of that. Then disassemble and clean the threads of both parts. Wrap the threads (at least 3-4 wraps) on the male part in the direction of the turning to tighten.

Then when assembling the parts turn to tighten until there is slight resistance. Run the compressor until it kicks off. Then check with soapy water. look for leaks then, and if so, tighten slowly until the leak stops. If the parts are tightened and then untightened the tape becomes faulted.

This can happen when assembling gauges, discharges or filters when trying to line them up.

.

[T...K21]

Did you check the rubber seal on the drain valve? it may have cracked or unseated when you tightened it after breaking it in.

[LCHIEN]

Primer on Air fittings

Most common places to use teflon tape in a home shop:
Air compressor to hose or female QD fitting
QD female fitting or male stud to hose
male stud to tool (such as - air nozzle, nailer, screwdriver/drill/impact driver etc, spray painter)

Note the male stud and female QD, the "sex" depends on the part that mates with each other. Depending on the hose and or the tool, the NPT fitting is usually a 1/4" male or female NPT. There's actually then four types of fittings:
Female QD with 1/4" male NPT
Female QD with 1/4" female NPT
Male stud with 1/4" male NPT
Male stud with 1/4" female NPT.
they also come in 3/8" NPT for higher flow rates but 1/4" is probably all you'll encounter.

To add to the confusion there are three types of QD/studs.
there's a industrial, automotive and ARO. By far the most popular is industrial. They're often color coded (orange, yellow, blue) with paper tags and if you stick to the same type you'll be OK, but by far the most popular is the Industrial - orange - that's all i buy. Blue is automotive, Yellow is a universal; the QD coupler supposedly works with the industrial, automotive, and ARO studs but I've never tried it. Physically they all look alike so look for the colors when you shop at HD, or Lowes. I think the HF stuff is the popular industrial and not marked.

my do's and don'ts for teflon tape.

its only for tapered joints - 1/4 NPT and the like usually used on air fittings. Do not use on straight threads.

use three layers or so

Don't cover the first thread... this keeps shredded tape from getting into the airway.

Try and wrap in the direction so that screwing it in makes it tighter, not unwraps it. - That means holding the male end in your left hand pointing right, start wrapping the tape under the bottom and towards you. Pull the tape tight so that you can see the tops and valleys of the threads clearly through the tape. Don't pull it so tight that the tape thins so much it separates. After three wraps I just pull the tape hard it'll stretch and break leaving the stretched and broken end well seated into the threads - no flying end. (actually, the wrap direction is not critical in my opinion if the tape is properly stretched on and the end pulled tight and seated like I described - I never had a problem but it won't hurt to wrap in the direction I described).

Once covered with the tape, thread the fitting into the female until it bottoms. and you encounter resistance. Then keep going another turn or so. THis will deform the tape to fill the gaps. Don't back it out, if you do this will release the seal the tape made and you will have to strip the old tape off and retape before putting back together. Tape cannot be reused.

I've never observed any leaks in my fittings after this.