Adjustable 12v Pressure switch

Submitted: Thursday, Sep 25, 2014 at 20:49
ThreadID: 109615 Views:4418 Replies:4 FollowUps:5
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Anyone have any ideas about getting an small adjustable pressure switch to put in line to control my compressor pump and make it cutout at around 40 PSI. The factory settings are cut in at 120PSI and cutout at 150PSI. As I am running the hose and hand piece direct from the compressor I want to drop the pressure cot off at around 540 to 50 PSI. Any tips appreciated. I am considering running small air tools for brief periods from it when in isolation, so would like the easy of increasing the pressure at a later date. Thanks
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Reply By: HKB Electronics - Thursday, Sep 25, 2014 at 21:02

Thursday, Sep 25, 2014 at 21:02
Something like this?

Pressure switch
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Follow Up By: Graeme S - Thursday, Sep 25, 2014 at 22:20

Thursday, Sep 25, 2014 at 22:20
Yes that is the sort of thing I am after but the description says operating voltage from 40 to 220 volts. Would it work at 12v?
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Follow Up By: HKB Electronics - Friday, Sep 26, 2014 at 09:05

Friday, Sep 26, 2014 at 09:05
Yes will work fine on 12V but you will need a relay to switch the current to the motor.
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Reply By: Member - John and Val - Thursday, Sep 25, 2014 at 21:14

Thursday, Sep 25, 2014 at 21:14
Graeme,

Suggest in the interests of safety, leave the existing pressure switch in place. This will allow you access to the present 120-150 PSI supply too which might be useful for air tools.

Drawing from that 120-150 PSI point I'd add a second pressure switch such as this one . It's a 30-50 PSI switch on Ebay, so that link probably won't work for ever. It's intended for mains voltages but could be used to control a high current relay to switch the 12V supply.

One problem you might face is that any pressure switch will have significant hysteresis, meaning that if it turns off at say 150 PSI, it won't come back on again until the pressure has dropped to 120 PSI. Likewise off at 50 and back on again at 30. You may need a bit of storage capacity to smooth out the supply/demand cycle too.

Cheers

John
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Follow Up By: pop2jocem - Thursday, Sep 25, 2014 at 22:24

Thursday, Sep 25, 2014 at 22:24
As John said leave the existing pressure switch in place but add a regulator as used by spray painters. Then you have the option of setting the pressure at your hose outlet to whatever you need. Higher for air tools and lower for whatever other purpose you require.
One of the uses I have for my on board compressor is blowing dusty air cleaner elements out. Not a good idea to blow holes in them with high air pressure.

Cheers
Pop
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Reply By: The Bantam - Friday, Sep 26, 2014 at 07:47

Friday, Sep 26, 2014 at 07:47
a couple ofvthings to think about.

Do you have a reciever or tank in your air system?....this makes any air system more efficient and makes working with a regulator more effecive.

Reducing the air pressure to 40 psi will make tyre inflation very very slow....to achieve air transfer you need a considerably higher source pressure than you wish to inflate to for it to happen with any sort of speed.

Any presseure switch you plan to use should use a realy to do the heavy 12 volt switching which will be in the area of 30 to 60 amps.
That means just about any pressure switch will do the job, if used with an appropriatly rated relay.

Yes there is the issue of hysteresis....all pressure switches will have a significant difference between when they cut in and out..this is unavoidable and in fact desirable, because it stops the switch from hunting and making too many stops and starts.

Most adjustable pressure switches will have either upper and lower limit adjustments or a pressure adjustment and a window or hysterisis adjustment..

personally I'd be adding a tank and a regulator.

This will reduce the number of compressor starts and stops increasing the life of both the compressor and the pressure switch, giving a smpoother air flow and the ability to have a small amount of air stored when the engine is stopped and compressor is not running.

The tank will also drop a lot of moisture and oil out of the air a filter reg will help here too.

The regulator will give you accurately regulated air pressure where a pressure switch will not.

cheers
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Follow Up By: HKB Electronics - Friday, Sep 26, 2014 at 09:04

Friday, Sep 26, 2014 at 09:04
There is some debate regarding tanks on small compressors, in a typical vehicle setup the tank is going to be small, therefore it is argued it will have little effect on the inflation time due to the large capacity of say a 4X4 tire compared to the tank capacity. It has also been suggested that the tank will actually slow inflation times as once it pressure equalises with the tire you then have to pump up then tire and the tank to the correct pressure.

Having said that I have a tank on my vehicle as it gives me enough capacity to give a blast of air if required.
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Follow Up By: The Bantam - Saturday, Sep 27, 2014 at 00:06

Saturday, Sep 27, 2014 at 00:06
I doubt that there is any advantege to a tank for tyre infaltion alone...unless the tyres are small........it is when you want to run regulated air that a tank comes into its own.....if you have the tank sitting at 100+psi......that is 3 times the air capacity when regulated down to 30PSI.
and having the tank there puts a buffer betwen the compressor and the reg..which is good for both.

There is a very good reason why almost all commercial workshop compressors run a tank.

cheers
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Reply By: V8 Troopie - Friday, Sep 26, 2014 at 20:56

Friday, Sep 26, 2014 at 20:56
I had an application that required pumping up to only 5psi (airbag suspension) which was very difficult to do with a compressor (too powerful) or a footpump.

So I bought that automatic inflator gadget that Ryobi sells at the big hardware stores.
The gadget's compressor is just a toy so I discarded that - I was after the electronics.
I rigged the gadget's pressure sensor into an air manifold to my compressor with a shutoff solenoid.
All I need to do now is connect the airhose to whatever needs pumping up - or deflating - and dial up the required pressure. Hitting the on switch does the job for me automatically now, the compressor stops when the selected pressure is reached.

Its a bit of a tinkerer's job but works fine for me, I was wondering why ARB or any other aftermarket gear company haven't come up with something similar yet. It sure makes it easier to change the tyre pressure for different terrains, one can enjoy that cuppa without having to watch a pressure dial like a hawk.
V8Troopie
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