Does the air compressor have to run all of the time when the locker is locked or just when it cycles between locked and unlocked??

 

Neither However you need pressure to activate the locker. the pressure is released to release the locker. unless there are leaks, the locker requires no additional air flow to remain activated.

 

Does a valve close in the air line to hold the locker engaged?

 

No. The air locker valve opens and allows the air pressure to activate the locker by moving a lock ring to the locked position. It is spring loaded to return when pressure is released. The valve has a small hole in it to allow the pressure to bleed off when the valve is in the closed position. Seems backwards, but it is a single function valve so it only has an open and closed function

 

On my ARB locker, the compressor has a small tank attached, tank not much bigger than my fist. A valve then either directs pressure to the locker, or vents the locker. pressure turns locker on, vent releases locker. The tank remains pressurized. eventually the air does leak a bit at the locker, in which case the pressure in the system drops and the compressor turns back on. the compressor then turns off after pressure is restored. I can run the locker for maybe half an hour before leaks require the compressor to kick in again, usually for a small number of seconds.

So you got two switches at the dash, on to turn on compressor, and when On I mean its circuit is active, so that compressor is controlled by its own pressure switch, if pressure drops below about 60 or 80 psi or what ever the pressure switch is calibrated for, the compressor will turn on, then off once pressure li it is reached (as long as dash switch is on) . The second dash switch activates the locker, but to activate the system must have pressure, i.e... the tank need be charged with air pressure for the locker to turn on once you trip the locker switch on dash.
Eventually leakage at the locker or elsewhere will cause the pressure to drop enough that the compressor automatic pressure switch turns the compressor on again, then off once pressure is restored.

So unless you got a big leak, the compressor is not continuously running while locker is engaged, but eventually tiny leakage at the locker slip ring will cause enough pressure drop to allow the compressor pressure switch to trigger the compressor on again.

I recall ARB instructions consider the system leak tight enough if you can go for 15 minutes or more without having the compressor kick on while locker is on.

My compressor is mounted in rear quarter behind the trim panel that the stock spare tire rests against. nice and safe inside away from grime and heat of the engine bay.. some place then under the rear seat, others in the engine bay. your choice.

 

ps.. consider your axle ratio before buying any locker. And of course axle ratio is determined by tire diameter. Dont by a a locker that cannot accomidate the ring gear size that you may eventually go to. if you have say stock gears, and by a locker to fit that set up, then later go to huge tires, you may find that the gear ratio you then need for those huge tires require a different sized locker. so pay attention to what size gears in a diff the locker is sized for, consider if you might have future plans for bigger tires, size the locker correctly so you dont do the job twice. I recommend you finalize tire size, and gear ratio for you build up prior to
purchasing the locker.

 

Get a Detroit locker and you don't have to worry about all of that.

 

Thanks
How many psi does the air locker require? I am working on plans for my overland setup and was going to install a compressor with tank for tires, etc and was going to run the locker off onboard air.

I am considering a Detroit or Aussie for the rear and a air locker for the front axle. If I had manual locking hubs in the front I would put a locking differential in both as I can could isolate power to the front diff via the locking hubs and transfer case when on the road in 2wd. but adding manual hubs to the xj is not cheap.

 

If it is ARB, then 95 to 105 psi.

 

Does anyone know what the scfm is on the ARB compressor?

 

I don't know right of hand, but they have a single and double piston available. They claim the double piston can be used to fill tires

 

You don't have to have manual hubs to put an auto locker in the front axle, I have a Spartan locker in mine and it works fine.

 

Auto lockers work fine without hubs. I have them in both ends of my XJ. However I would suggest that an ARB would be too much for our 27 spline D30 axles. It is a sure recipe for axle breakage on something like the rocks in Moab or Sierras. So exactly what do you have in mind for tires etc

 

I got a 20 year old arb single pump. 33x12.5x15 tires. 4 minute fill time 12 psi to 30 psi. Friends new dual piston arb pump does it in 2 minutes.