Using LPG bottles as air tanks.

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moltenfire, Apr 21, 11:53am
As these are TP'd at 3.3MPa (475psi), is there any reason why they can't be used as air-tanks? These are the big ones 90kg and I need to increase my air storage to reduce the stop/starts of the compressor.

gunhand, Apr 21, 12:24pm
Ask in motoring, very clever bunch in there and will know.

tweake, Apr 21, 1:03pm
pressure wise should not be a problem. i'm not sure what thread they use.
you will have to use them upside down as they have no drain valve
or use a water removal setup before the tank.

dastedly, Apr 21, 1:58pm
One big thing is all gas need to out of it. just stand bottle upside down and feed air in that way and feel it from other port on compressor ,not from the way the outlet hose hooked in . the any water that gets in gas bottle will go back to compressor tank .

tegretol, Apr 21, 2:06pm
Are they able to withstand constant changes in pressure ? I think they would be designed for a gradual change, like as the LPG would be used slowly but as air tanks, they'd be up and down a lot more?

mrfxit, Apr 21, 2:45pm
Shouldn't be a problem.
I regularly use an old 60ltr stainless steel LPG tank as an extra air supply tank.
I reused the original fittings including taps etc
The compressor has twin tanks set up that pumps air to 1 tank & that tank feeds the other tank which also has the outlet on it.
Only the 1st compressor tank has ever had water in it & never had water in the supply tank.
Rare to find water in the 2nd compressor tank

trade4us2, Apr 21, 3:09pm
If you happen to have 120 metres of 1" steel pipe lying around, that's about 60 litres and would stand higher pressures.

tegretol, Apr 21, 3:47pm
True but then you have 40+ fittings to leak!

supernova2, Apr 22, 5:23pm
I've been using an old forklift sized LPG bottle for my compressor for about 10 years and it's fine - so far.

bill-robinson, Apr 22, 7:47pm
i have a lpg tank from a car that I use. works fine, and has done for 15 years

sr2, Apr 22, 8:02pm
If your compressor is not big enough a larger tank will not be a solution, what are you using the air for?

bashfulbro, Apr 23, 9:21am
I went to a truck wrecking yard, and bought an aluminium air tank off a truck, it polished up like new.

tegretol, Apr 23, 9:25am
Compressor is rotary 40cu feet/min used to supply an oxygen concentrator. Need a large volume over a short time and more tanks will reduce the number of cycles.

tegretol, Apr 23, 9:25am
What pressure do truck brakes run at?

tweake, Apr 23, 5:51pm
what controls does the roatary have ?

i don't know what size tank you have all ready. a lot of small rotaries come with fairly small tanks.
might pay to go get a tank off a fairly big piston compressor. a tank would be 3-4 times bigger than a 90kg lpg tank.
a few pop up on TM now and then. but would not hurt asking around the importers.

tegretol, Apr 23, 6:15pm
Controls? On/off switch plus a pressure gauge. It's a 10HP unit with a 270L tank (Ceccato CSA 10/8). Plan to add at least six of the 90kg bottles as air receivers and get it up to a total of 1500-ish litres which in theorey will nearly 1/4 the number of starts/stops.

sr2, Apr 23, 6:20pm
Fair enough, make sense.

daves01, Apr 23, 6:44pm
Or if you look around you might be able to use bigger old lpg tanks. We have a pod at work that can't be refilled (officially) due to some change in the regulations which technically makes them unusable .

tegretol, Apr 23, 8:15pm
Mmm, now there's a thought. But I already have an abundant supply of the 90kg bottles.

tweake, Apr 23, 8:44pm
what pressure do you need for the oxygen unit? (or system pressure)
whats the max and min pressure on the pressure switch ie what pressure is it turning on at and off at?
just wondering why they are running on/off instead of load/unload.

your theory is right, but the other factor is pressure differential.

tegretol, Apr 23, 9:02pm
Ah OK. Compressor starts at 90psi and stops at 135psi. The oxy concentrator gets upset at anything below 85psi. When it's under full demand, the compressor does keep up but is cycling about every 2-3 minutes. I reckon that increasing the receiver tanks by a factor of 4 should extend the cycling time by a factor of 4.

tweake, Apr 23, 9:22pm
sorry i clean forgot to ask what duty cycle? how long does it run and how long is it off before starting again/

135 psi sounds really high, but i don't know your model. would need exact model number to find the specs.

your doing well to have a 85psi run pressure and a 90psi minimum. only 5 psi drop through all the filters and dryers.

otherwise increasing the storage is the way to go. fit it as dry storage (ie after the dryer). that way you should not need to worry about them getting oil or water in them.

ceebee2, Apr 28, 11:58am
I have done exactly that with an air compressor. Max PSI for air will be 120 so way under max tank spec.

mrfxit, Apr 28, 2:01pm
Will be plenty good if only needing modest bursts of good pressure.
Painted a few cars etc with enamel paint via my own twin cylinder poppet valve compressor + 60 ltr tank (no, not in recent years)

mrfxit, Apr 28, 2:02pm
Fair enough, but will prolong the time it IS running