air compressor req'd for positive pressure in container 1

[skier1]

I Have an enclosure that is located outside close to San Francisco. The container is 60 cu. ft and to keep the air dry inside we have purchased a de Walt Model d55153(tank cap.4 gallons) air compressor with an air dryer purchased from mcmaster carr. The container is completely sealed and we just want shut the compressor off once the container has positive pressure of 10 psi. The air pressure going from the filter to the container is just 20 psi.The problem is that we cannot get up to the 10 psi and the compressor runs continuously. Do we need a compressor with more tank capacity?
Thank you

 

[MintJulep]

What type of container? How is it sealed?

 

[IRstuff]

Sounds like you have a few problems. The first is that your box appears to be leaking like a leaky sieve and you apparently haven't even thought to check it for leaks. Your compressor is rated for 4 CFM at 90 psi, and 5.4 CFM at 40 psi, so it's pumping out a large amount of air into the filter and box.

What's the pressure drop across the dryer? Are you dropping a full 70 psi across the dryer? What's your outlet pressure from the compressor?

TTFN

FAQ731-376

 

[berkshire]

skier1 (Mechanical)
You do not say what you store in the container.
However for the purpose of finding the leak if you set off a smoke cartridge inside, close everything up and start your compressor, you should literally see where your leaks are. You can obtain smoke cartridges at HVAC supply stores.
I do not think you need a larger tank on your compressor, it sounds more than adequate for the task.
B.E.

 

[chief]

Ensure you have a check valve in your discharge pipe to the container.

Offshore Engineering&Design

 

[jistre]

Hmm... Given that you're having leak problems, I have to ask: Is the container even designed to hold 10 psig, or is this something that is being tried as a new approach to an existing problem? I have to think that if this vessel is designed to hold a 10 psig blanket, it would be designed to maintain that pressure over its expected operating conditions. 10 psig might not sound like much, but assuming a perfect cube, each face of the cube is going to see a load of 22000 lbf or so at 10 psig. I sure wouldn't want to be anywhere near it if it's not designed to handle it.

If I'm misreading the situation and the vessel really is designed to hold that much pressure, then I definitely agree with chief. Get a PSV immediately upstream of the vessel as step one. If you do manage to seal your leaks up and get the system running, and the compressor control to stop it at a vessel pressure of 10 psig fails, then the compressor is probably going to run until it gets the whole vessel to its internal cutoff. If it's able to do that until everything is at 20 psig, then you're getting into ASME Boiler and Pressure Vessel Code ranges. Your vessel might not be covered by it, but the fact that you'd be in the same potentially lethal pressure ranges in a failure would give me pause.

 

[RossABQ]

If the purpose is to keep salty sea air out of the enclosure, 10 psi is WAY overkill! 10 INCHES w.c. would be more than adequate, 2" or 3" would even be adequate. As noted above 10 psi is close to pressure vessel territory. It will just leak faster.