On Board Air Tank - Follow Up

Stuart,

Like you I am no guru when it comes to air compressors but I have been looking at the idea of a larger air tank for use on the vehicl. I have an ARB Compressor fitted to the car, this has a small tank attached from ARB.

I have spoken with the guy from the local 4wd shop who is well regarded in the industry. Think Outback Challenge.

He said to use a flexible hose as it will cause less problems when it DOES work loose. The other thing that I am going to do whem I fit the tank is to connect it to the compressor with snap on fittings the female (shut off ) on the compressor so that I can disconnect and remove the tank and still use the compressor. (My 4wd is the family bus and I don't keep all my touring accessories in the car all the time cause they often just get in the way, eg. when I neeed the third row of seats.)
Also this will allow me to isolate the tank when I don't need it, why inflate the tank to 40psi when I don't need to? The other thing I am considering is a shut off valve in this line as well, just to make the isolation process easier. When all this is sorted I intend to put fittings on the front and rear of the vehicle so I can connect a hose without having to access the compressor.

Finally, if that 15 - 25 sec of air is before the compressor cuts in again I think that would be very useful.

Keep up the experimenting, I am interested in the results.
Duncs

Stuart,

I reckon the volume of a tyre is about 30L (assuming an 8" wide tyre on a 16" rim with an outer diameter of 32"). To double the pressure of air in the tyre from atmospheric pressure to 1 Bar or 15 PSI you would need to add 30L of air. So your 6L tank at 5 Bar would barely get a flat tyre up to 15 PSI. A 30 L tank at two Bar would inflate a flat tye to 1 Bar or 15 PSI. A 30 L tank at 4 Bar would inflate a flat tyre to 2 Bar or 30 PSI. A 30 L tank at 6 Bar would inflate your flat tyre to a useful 45 PSI.
So a 6 L tank is pretty much a waste of time and effort (unless you can store air at about 200 Bar which is what scuba cylinders do).

Place a one way air line filter between the tank and the compressor. This will stop all the back pressure on the compressor and make it start easier under load and also stop air leaking back through the compressor when it's not running.

Stuart
-1 As Mark says install a check valve between comp and tank ¼” bsp/npt would do the trick, get from comp shop, truck brake place or Blackwoods.

-2 Having a volume tank (receiver tank) is a good idea, because if you roll a tyre off the rim you need the volume to get it started back on the bead of the wheel.

-3 Mount the tank/switches etc where you will, but mount the pressure relief valve/blow off valve on the tank or real close to it, buy hose from truck brake shop with push-loc fittings think swag-loc do them.

Just out of curioisity what is your tank made from?

I was thinking about making a tank from an old fire extinguisher.
Do you think this would work??

G'day Stu

I think it was Boyles 1st Law of thermodynamics ... P1V1=P2V2.

Hence 6l at 110 psi = 18l at 36.666666667 psi. So if the volume of the tyre is 36l then it will only be inflated to about 18.33333333 psi. Get my drift ??

Cheers

Stuart,

My daily bread comes from working in the pneumatic and hydraulic industry, so here's a couple of tips:

A check valve in the line between compressor and tank wont unload the compressor. It will still be starting against whatever pressure is in the tank PLUS whatever the spring rating is that is part of the check valve.

I've installed a manifold in the GQ with additional ports, one of which is fitted with a solenoid valve that when I flick the switch opens the compressor line to atmosphere, thereby truly unloading the compressor. Mainly used for free running to help cool down quicker.

You can place the compressor, tanks, valves etc in any parts of the vehicle, as long as the connections are correct. The best way way to connect it all up is to get some proper polyurethane tubing (6mm) from someone like Festo, SMC Pneumatics, Norgren etc along with the right fittings, and then just install the tube inside some protective sheath, the stuff you put around electrical cables. DONT use copper as it will work harden and fracture very quickly. I've got the compressor on the firewall, under the bonnet, manifold on the other side of the engine bay and air outlets at manifold, bull bar and rear step. One outlet is connected to a pressure regulator & gauge that I can adjust for the tyre pressure required. That way I can set it to road pressure and not have to watch it every second. 150psi in a tyre would go off with a hell of a bang!

The point about Boyles Law is valid, and once exhausted, the tank is just another void for the compressor to have to fill, along with the tyre. Too much time.

You could change the cut-in set point on the pressure switch but there's no point, as the flow rate slows proportionally to the pressure diference, so as the pressure drops lower in the tank, so too the flow of air from the tank slows down.

Hope this helps, and for the record, I've got an ARB compressor that does a 31.5 10R 15 tyre from 16psi to 40psi in 3min 20sec. No problems doing my four tyres and mates as well.

Regards,
Keith

if you own a max air , why get a air tank , its so quick anyway on its own

Hey ALL,

Keep those ideas coming and thanks for the input so far.....

Stuart

I still reckon it's a top idea, as said above blowing air filters out, cleaning things etc perfect. And there is nothing wrong with a headstart when pumping your tyres up. And what about the time the compressor is running and you are checking pressures, putting caps on, and just generally buggerising around between tyres, at least it's not going to waste.
Also (and this is the main stupid male big kid reason for me) is that I would love to hook 120psi up to my air horns and bleep off the crappy compressors that came with them! LOL
I've run them through my 240v compressor at home and holy crap they are loud.
Also if I go air lockers down the track, I can just plumb them straight in.
The Blue Tounge will restart at 100PSI so I should'nt have a problem with it.