Installing compressor "Off" switch?

As far as I am aware, these little compressors just run constantly, when turned on / released from the valve, the air keeps coming out, so can't back up and over pressurise the airline.

I take all caps off and just whip around, using a 10' airline extension so I don't have to move the compressor where placed in front of the vehicle.

If you want a cut out (and the ability to enable more tasks from compressed air), you install a small airtank, put a pressure switch on it, and this will cut power when it reaches it's setting, turn on when you go to next tyre to inflate, and so on.

This is one of my mid term mods to do, once I source a decent little 9lt or so air tank.

Not hard to do, just purchase a pressure switch off Ebay, you'll need one that turns off the compressor before it reaches the max pressure the compressor rated for.

You'll also need to a relay to switch the motor current, the pressure switch operates the relay.

A small tank does hurt but you'll will get a bit of debate about whether they are worth it, I have a small 9 Ltr tank which works for me.

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Hi Mark,

The compressor you have purchased is like most compressors marketed for tyre inflation. They are "open-ended", that is their hose and chuck are open when not connected to the tyre valve. In this way they keep pumping air when not connected and the air blows free and no pressure builds up in the hose or compressor.

Whilst the compressor is "blowing free" the electrical current of the compressor motor drops to a lower value and in fact the easy passage of air through the compressor helps to cool it down. So you can see that there is little-or-no need to switch the compressor off during this short time where you are presumably moving to the next tyre. Nor is there need for a remote control.
Having free air blowing out of the hose may also have the benefit of keeping sand from entering the chuck when off the valve.

Adding a pressure switch to your setup would not only be a waste of money but it would not be called upon to work anyway as the pressure will not build up to operate it because of the open-ended hose. A pressure switch is appropriate where an air receiver tank is employed to halt the motor when the pressure has reached a full tank.

A pressure switch is used with systems where the hose shuts when removed from the valve and often with a receiver tank.
Pressure switches are also employed on compressors that are being used with differential air lockers where air is only occasionally required when the locker is called upon to actuate. The stored pressure in the system is then enough to maintain the locker actuated and the compressor motor automatically switches off until next needed.

I can't help you about the pressure switch as mine already has a pressure switch. It's a Bushranger Max and that is the reason that I chose that one because of the switch. It doesn't have any tank on it just the hose and handpiece that shuts the air off, runs for a few seconds then shuts off after releasing the trigger. I love my bushranger.
http://bushranger.com.au/product/max-air-iii-compressor/

To add to the discussion as there are some older members on the forum who are very set in their ways and not open to new ideas:)

I have my compressor permanently mounted onboard, it is controlled by a pressure switch and has a tank of around 9 liters. I have installed a Nitto quick connect socket on the rear of the car, one on the trailer draw bar, and one on the back of the van, the air hose plugs into these as needed. The air hose also has a Nitto quick connect socket and my air tools are fitted with quick connect bayonets.

I find this setup convenient as I can turn the compressor on at the start of the day and forget if I will changing pressure often. To inflate a tire it is simply a matter of plugging the air line into the socket, connect to the wheel, set the inflator to the desired pressure and off it goes.

Contrary to some I find the tank a very worthwhile addition, it provides a useful reserve for blowing out filters and dusty things, seating tires and for running air tools for a short time. I also use an air duster gun to clean the back of the camper before setting up the ensuite and again the tank provides a useful reserve. I also find the tank is advantageous when inflating tires as when one tire reaches pressure, while your disconnecting the hose coupling and putting on the cap and moving onto the next wheel the compressor continues to run and charges up the tank which gives an added blast to next tire and reduces inflation times.

The rating of air hoses is an interesting point, but usually the compressor specs will say maximum inflation pressure of 150PSI for instance, I just had a quick look on Ebay and one stated 200PSI, that's 80PSI higher than the safety zone of my large 240V compressor! One would hope if the compressor is rated for 200PSI the supplied hose will also be rated for 200PSI.

As for the curly plastic hoses, the first thing I did was to throw that away and use good quality airline and a good quality rubber hose for the air fitting. I do somewhat agree with the statement that the pressure switch should be rated for the air hose, it should be rated for safe operation of the compressor, air hose and tank if fitted ie rated below the max pressure of the item that has the lowest pressure rating.

Another thing to keep in mind is the rating of the compressor, some have a specified duty cycle, ie they are not rated for continuous use. Also when running the compressor for long periods of time at high pressures the output of the compressor will get very hot so make sure the connecting hose can withstand the heat or have some sort of cooling arrangement on the outlet of the compressor.

Yep , good idea but I would not use that one until you ensure it has high contact rating. Its switch rating psi is a little high also (90-120).

If you search for ARB one then it has 30 amp contact rating and is dearer .

I use one and its good to auto switch off the compressor after I inflate tyre when moving round to next wheel.
In practise switch off effectively improves duty cycle and gives a little piece and quiet between wheels.

ARB one typically averages about 85 psi operation also (70-100psi)

Stay away for a day- come back to a novel! Thanks for the input people. Much appreciated.

I don't believe this unit has to continually run, most of the similar designs have a pressure switch which cuts out when the air hose reaches pressure. My old ARB unit does the same (not the unit with the tank and it is definitely a cut-out when the hose reaches pressure). Having said that, I really wanted a different unit. Such is life.

I am not certain of the use of a pressure switch requiring a relay, (bear with me, the words auto electrical and competent are unfamiliar territory) shouldn't the existing switch already be set up for this? Why would wiring the pressure switch direct into the existing switch be any different?

If I go for a remote switch will I have the same issue (having to wire in a suitably protected relay)?

As I said earlier, I am not wanting a remote tank.

Cheers,

Mark

I never knew blowing up tyres could be so complicated. I have an ARB compressor mounted under the bonnet. It was the one they were using for their air operated diff locks when I bought it years ago.

To use it I have a wire with an alligator clip on one end that clips onto the battery and a push on terminal at the other end that goes onto the compressor. In the middle is push button hazard light switch from a VP Commodore. When I press the button the compressor starts. When I push it again it stops.

I connect the air line to the tyre and press the button. When I think it should have enough air in it I press the button to stop it then walk around and check the pressure.

I suppose doing it that way these days is like using T Ford technology but the tyres get inflated and I get a bit of exercise. It helps to prevent me from seizing up.
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I mounted an old ARB compressor in the back of my old wagon years ago. I intend to do it again in exactly the same way as it worked so well. As said above, the compressor did chew the power and you would notice the rpm drop significantly when the car engine was shut down, so I mostly left the car idling when I wanted air.

The power to the compressor ran via a guarded switch to prevent accidental activation, to a relay that was switched by the pressure switch sourced from ARB and was made for the compressor when it was installed to run airlockers.

I run lots of air tools at work and 90psi seems to be the standard for tools, air lines and regulators with a sufficient safety margin, so I'd be more than happy using 90psi switch. A hose splitting will be noisy, but won't do much damage as the volume of air is low, pressure tanks on the other hand can be spectacular so I'd be hesitant to include one due to the potential for internal corrosion, if I did it would be rated for use in a similar application. Truck air tanks are popular and I have seen small fire extinguishers put into service.

The old compressor had an approximately a 500ml integral pressure tank, so didn't hold a lot and was pretty much a waste of time. I ran the outlet to a brass T with the pressure switch screwed into 1 port and a self sealing air fitting on the other.
I could pull up, flick the switch and have the compressor get up to pressure while I dug the air hose out of the back of the wagon.

With around 8m of air hose, the male air fitting to plug into the port at one end, a tyre valve fitting on the other and a small inline valve around 12" from the tyre valve end it was ling enough to reach from the back of the wagon to the front corners and trailer.

I think it was the inline valve that made all the difference as the compressor was relatively low capacity, it allowed the line to be pressurised, rather than having to wait for the compressor to pressurise the tank and 8m of hose before pushing anything into the tyre and essentially tripled the capacity of the tiny air tank if you needed to blow dust out of something.