Extra Large Tank on Small Compressor?

[bad_idea]

I have a 20 gallon direct drive compressor in my garage. It handles most work I do - impact tools and the like. But I have an air hoist hanging from the rafters for hoisting things into the loft that is an air hog. I can get two or three lifts out of the hoist before the tank is down below a workable pressure. I have a 100 gallon propane tank out behind the shed looking for a new home. I am thinking of sticking that propane tank in the loft plumbed in to the hoist. I am waffling between plumbing the tank in all the time or having it isolated from the main system except when the hoist is in use.

I know water in the propane tank is a concern as there isn't a drain on the bottom. I figure I can put it in the loft upside down with the inlet coming up from the outlet of the tank on the compressor. Figure the moisture will drop back into the primary tank.

Thoughts?

 

[cherokee]

I think I would cruise the local ad's and look for a compressor that someone is selling cheap with a bad motor or pump. Then water test it to make sure you are not building a bomb.

 

[bad_idea]

I think I would cruise the local ad's and look for a compressor that someone is selling cheap with a bad motor or pump. Then water test it to make sure you are not building a bomb.

What is your issue with using the propane tank? Propane tanks typically run upwards of 200 psi. Unlike a used air tank, I am confident it will not have rust issues inside from water.

 

[Walkers]

It doesn’t really matter what you do, that 20 gallon compressor will die after very little use. You will likely exceed its duty cycle by 500% and the pump will be puking it’s guts out.

 

[bad_idea]

That 20 gallon compressor has been chugging along in my garage for 20 years now. It was used when I got it. At this point, it owes me nothing. The oem cooling fan broke off 5 years ago when I moved to this house. I wired a box fan to blow on the compressor head whenever the compressor is running. I know the thermal overload switch still works in it because I ran a whiz-bang pump off of it last year to drain the pool for about an hour or two and it cut off once or twice then. Honestly, if it dies that's a great excuse to upgrade the compressor.

 

[laser3kw]

"small" compressors are usually designed around a low duty cycle. On / charging for a short time, off for a period to cool motor and compressor. If you attach a large receiver tank, the motor and compressor will run for extended time to refill the added volume. That will shorten the life of the motor for sure and I'm sure the compressor will not last.
The upgrade to a larger compressor is a great idea - then add the extra receiver.

 

[timgunn1962]

Biggest problem I can see is that you have a 100-gallon that currently contains Propane. Even if it's nominally empty, it'll still be full of Propane at atmospheric pressure. You then propose to pressurize it with air so that it contains a compressed Propane/Air mixture?

Lower and Upper explosive limits of Propane in air are 2.1% and 9.5%. At "about" 100 PSI, you'll have a bomb. You'll still have a bomb until you've run something over 5 complete pressurize/depressurize cycles (i'd want at least ten, personally). Depending on where the ports are on the Propane tank (or where they can be, since you've obviously thought about draining condensate), you might be able to fill with water to displace the Propane, then fill with air to displace the water, thereby avoiding an air:fuel mixture. If you only have one port, it'll need to be on top to release Propane when you fill it with water and on the bottom to drain the water and allow air in. Inverting it with 100 gallons of water in may or may not prove awkward, depending on the equipment available.

 

[bad_idea]

Good call on getting rid of the residual propane in the tank. It has two ports on top - one 3/4" NPT and one 1" NPT. I'll pull both fittings, fill with water, and then siphon the water out by dropping a hose in to the bottom. I'm a shipyard competent person (the guy that certs tanks safe to enter) and will use my meter to check for LEL after a drain and fill of water.

I appreciate you all's concern on the 'little compressor that could' shitting the bed from extended run times. I'm not sure this compressor knows how to die. If it figures it out, then I'll get a new one.

 

[cvairwerks]

Pull the fittings, allow to vent for a couple of days and then wash out with some water and ammonia. Flush well and allow to dry. Add a valve so you can valve it off when you don't need it. When you decide you need it, make sure the compressor has good cooling air.

 

[cherokee]

What is your issue with using the propane tank? Propane tanks typically run upwards of 200 psi. Unlike a used air tank, I am confident it will not have rust issues inside from water.

I don't really have an issue against it, it is just that the compressors that are dead around here are so darn cheap, or free if you come and get it. They have the legs and little platform on top if you need it, and all the fittings you need. I just see it as more easy. Plus if you have a nice big propane tank I would rather use it for that, it seems harder to come by around here over old compressor tanks. Cleaning the tanks and filling them with water to test does take some time, but that is about it.

I would give my left......well you know for a nice 100gal propane tank. Last one I looked at was $400 and did not look that good.

 

[bad_idea]

I have no need for a propane tank. It came with the house, it had a ventless fireplace in the living room that used it. I deleted that fireplace, have never been a fan. The tank has been sitting behind the shed for 5 years now. Around here junk air compressors dont come along very often and when they do people think they are gold plated. A used older quality compressor is a rarity for that matter. I'll end up buying a nice new Quincy unit when this little monster finally dies.

 

[bad_idea]

Well, looks like this is going to be a non-issue. I did a search of marketplace on a whim and found a Quincy 325 for $500. I'll need a VFD to power it, as it is 3PH. I would imagine the 325 should be able to stay ahead of the air fall, but may add the additional tank if it proves to struggle keeping up. Not sure on the CFM rating on the fall, but I know the 325 can put out 18 CFM.

 

[u2slow]

+1 on duty-cycle concerns; i.e. long run time.

I'm about to add tank capacity to my 3hp/20gal compressor, but I know this model (HP and CFM) is offered in a 60gal, so I know I know it can handle the extra run time.