Minimum useful air tank volume

TP is test pressure..ie the pressure the cylinder is tested to. Note it is NOT the working pressure.

How big a tank you'll need is dependant on how big your tyres are.....are they 10" or are they dumpster truck tyres? Not being sarcastic but emphasizing that tyre size is relative to how much air is required.
If your using a airconditioning compressor as the air compressor then cylinder size is not important. Dont believe its important with the mini compressors either as its only time (minutes/hours) that is required to pump tyres to 35 psi.
No doubt there'll be more usefull replies to your question as time goes by.Richard

If it helps, I made up a tank to use with a Blue Tounge compressor, 300mm dia x 450mm long to run my diff locks, it took about 5 min to fill, good for seating tyres back onto rims but once it lost that inital burst was back to pumping at 1 psi.

The compressor had a 120 psi cut out, I never bothered to work out the volume cause I didn't know how. The wall thickness was 6mm with welded caps on each end.

Gary, I have a truck air brake tank off a small truck (mabye Mitso or Isuzu). It would be around 300mm diam x 350mm long (19 litres ??). It is run off the arb and uses the cutout to limit pressure to 100 psi. It is enough to pump one tyre from about 18psi to 30psi, as I tested a couple of days ago. Takes about 2 minutes to fill to 100psi.

Good for reseating tyres, or it will operate my diff locks for ages should the compressor crap out (if I remembered to leave the tank at full pressure at the start of the day).

Don't forget a shut off valve between the compressor and the tank as it will leak the pressure back through the piston on the compressor over a few hours.

I reckon you would need a mega tank to do all four tyres.

Hi there.

I have had 2 troopies over the past 15 years and both had blue Tongue compressors before I fitted an A/C type compressor, to both.

My observations are basically the same as already stated but I now state appears to have been over looked.

(1) 12 Volt compressor: With an air cylinder, as stated you only really get benefit with the first tyre but when the pressure in that cylinder drops to the existing tyre pressure, you now have to fill up TWO vessels (the cylinder and the tyre) to the desired pressure, as the total volume has increased. In effect the cylinder is now working to a degree against you.

(2) A/C compressor....Only way to go :-) A cylinder is really a necessity rather than an option.

Before anyone jumps down my throat let me explain why.

The A/C compressor does not in most cases have an oil sump and thus it has to be lubricated by pouring oil (about 1/3 pint) directly into the compressor via the plug on the body.

As the compressor works it pumps the oil out quite readily either as straight oil or as oil vapour. Either-way this is not a desirable event for the tubes.

Now if you have a storage cylinder, a truck brake size is good, fitted preferably some distance from the compressor and you can draw the air from the top of the cylinder, then there is a very good chance the the oil vapor has by now liquefied and/or any oil travelling down the air line fall to the bottom of the tank reducing the oil discharge considerably.

In my setup, I have between the compressor and the truck air cyl a small intermediary cylinder/manifold made up of a 6 inch length of rectangular thick walled tubing. This manifold has an oil drain tap, and the blow-off valve set to 120 PSI.

This system works so well that the air coming out of the brake cylinder is oil free to the extent that when I blow air onto my fingers and rub them together I can not feel any oil, there is a small amount of water vapour, but I can live with that.

I hope this helps in you decision.

Regards

how did you mount the air conditioner compressor to the land cruiser safe driveing mal

Hi GaryInOz,
Lots of great comments and ideas, but I was surprized nobody pointed out the mysterious. It is a fact about air pumps and receiving tanks that if the connection between pump and tank is on the opposite end of the tank from the outlet connection, then somehow the pump capacity is increased. I believe that this applys only when the outlet is being used and the pump is pumping. It does make sense to keep the inlet and outlet on opposite sides of the tank. Perhaps an industrial air compressor guru can explain this.
Another disturbing fact is that a tremendous amout of energy is stored in a compressed air tank. If the tank is pressed up to full value then the sun heats it you are really asking for vehicle/personel injury if you dont have a safety relief valve installed where it cant be shut off.
As metioned before quite a few necessary additions are required to your air system to make it right and make it last. Safety relief valve, pump inlet filter, pump oiler, pressure gage (or schrader fitting to measure pressure with tire gage), pump outlet water/oil filters, tank drains (auto or manual), check valve between pump and tank are really necessary.
Years ago I installed a small tank with copper lines in my car trunk to press up my air shocks. Ignorance is bliss. After seeing industrial application copper tubing fail so easily under vibration conditions I believe that copper tubing has absolutly no business being in a 4x4 in Australia. Stainless tubing or steel pipe is the way to go for all connections.
Some comments on your original question.
Taking a tire from 0 to 15 psig requires adding 1 extra volume of air into the tire.
I just measured my car tire a 4highx6widex60middlecircumferance inches or about 2040in^3 or 33 liters. So it would take 33 liters just to get it to 0 psig. Add another 33 liters takes it to 15 and another 33 liters for 30 psig. Another 10 takes it to 35 psig for a total requirement of about 76 liters. (I think Len Beadle said it took about 450 strokes on his manual air pump to press up one tire.)
You have 21 liters to work with in tanks that were once tested and proved to hold 150 psig (TP) but built to be used at 100 psig (WP) More than likely the existing blowdown (I hope they are really relief valves not water blow down valves) valves are set to 125 psig. Thus it should be possible to safely press those tanks up to 100 psig.
0 = 21 liters
10 = 28
10.7 = 30
15 = 42
30 = 84
35 = 98
60 = 168
90 = 84 + 168 = 252
100 = 280 liters of air
120 = would be 336 liters but dont take the tanks that high
At first look the 280/76 would yield 3.6 tires but that would entail draining the tanks to 0 psig but you have to stop at 35 (acutally higher so air will flow from tank to tire). So we only have 280-98 = 182 liters available as the tank pressure drops from 100 to 35 psig. At 76 liters per tire you would get just 2 tires done and be leaving 98 + 30 = 128 liters in the tank at a pressure of 45.7 psig. The second tire would have been slow to fill.
What happens when the tank pressure drops to the pump motor cut in pressure (assume 90 psig)? If there is no check valve between tank and pump the pump piston will have 90 psig on it and the motor will have to be able to overcome that 90 psig to stroke the piston. If it is an electric motor it will likely stall and burn up since it was probably designed to start with 0 psig on the piston. An electric motor does not build up much torque until it is running full speed, thus the need for a check valve to unload the piston via piston leakby
To summarize; your tanks will do a couple tires, but do be careful and be sure you get working relief valves on each tank, and since you will have to run the pump while filling tires you should have the inlet and outlet on opposite sides of the tanks. I am not certain if putting the tanks in series would also add to the effective pump flow rate, but I bet it does.
later, slater