Petrol powered air compressors

[flyingbrick]

Just wondering how these govern air pressure- do any drive the pump fulltime and use a relief valve to simply vent air once at max psi or is there more advanced trickery happening.

Experience appreciated

[Tumeke]

My bach compressor (1960s probably and certainly not industrial) automatically turns off the mighty Briggs and Scrap-Iron at a pre-set PSI. It then automatically re-starts (air starter) when drops below a second pre-set PSI. Hope this helps? I'd have to pay more attention to it when I'm at the bach next time if you need more info.

[flyingbrick]

Thanks man.. thats way more advanced than i was expecting! Just have access to a perfect tank and pump for a conversion and as i use it very rarely i think full start and stop probably isnt necessary..

Maybe pressure sensitive throttle could work with a centrifugal clutch to disengage pump... i havent googled this or looked for parts yet

[BLIZZO]

ask dolan, hes got a lush old girl that was an electric compressor that his brother put an old stationary motor on, i used it hooked up with my compressor also to paint my car, the engine doesnt shut off but i cant remember if it disengages or bypasses, it doesnt hiss like fuck when at peak pressure so must disengage but yea ask him fo sho he will tell ya 

[CaMpylobacter]

yeah my one was just an electric jobby that my bro had lying round in my lockup which had no motor and I bodged a briggs onto it and made a hori belt tensioner. 

fitted an unloader valve from a late 70s/early 80s mercedes truck to it - when it gets to pressure(120psi) it just unloads to atmosphere. it chuffs away til the kick in pressure (90psi) and then starts pumping again. 

It's a fairly lol apparatus. doesn't run at ideal rpm when pumping so is a little slow but it's been a bloody handy bit of kit to have (only owes me the cost of one pulley and a belt) to chuck on the ute when you're going to pick up a parts car or need to pump some tyres up or some shit. have seen it used to power a truck and trailer's air system to get it back to a depot when the compressor on said vehicle fucked out. strapped to the deck with it running. lolz. 

 

most 'professional' ones will run an unloader that has a pilot port which when the compressor unloads to atmosphere, it'll charge a wee air ram which will cut the engine back to idle. this also acts as a soft starter for if you're trying to fire the engine up when the tank is at half pressure etc so you're not fighting the pumping action of the compressor head - mine's nowhere near this flash. just runs at constant rpm and is a cunt to start unless it's dead flat ha

 

this is what my unloader looks like. 

one pipe in

one out

one exhaust. 

you can get silencers for the exhaust too but aside from the PISSSSH when it initially unloads, the rest of the noise is much less than the engine makes. 

 

you can get these cheap enough from china. genuine wabco ones are about $600 hah. 

I scored a brand new wabco one for free that was in some obsolete stock from an old place of employment. 

you could probs score one secondhand off pretty much any older merc/man truck that doesn't have an air drier (army 2228s etc etc. i think even the mogs probably run them). pretty much if the truck goes PSSSHHHH CHIT CHIT CHIT CHIT CHIT CHIT CHIT CHIT CHIT when the compressor kicks out it'll have one hah

 

if you have to pay for a new one then you may be best getting the flash harry type with the little air ram to return to idle. 

sometimes we get decent specials on brand new ones. I recently scored a hellishly good deal on a brand new petrol powered compressor for me bro that'll happily run his 3/4" rattle gun etc. they're about $3k now but he paid just under half that in the end! 

[flyingbrick]

Thanks guys! Thats exactly what i was wanting to know!

Hadnt thought about unloader valve (and non return)- good points. Time to mash ali express

[Mr Vapour]

I have a old.broom wade at home was a 3 phase. It's completely mechanical. The motor runs at a constant and It has pressure unit that is controlled by the crank case pressure. This connects to a rod that works on a rocker on the head to open a Valve in the head so the cylinder free runs with out compression when the tank is full. When pressure drops the valve closes and the pump works. It also.Has a mechanical valve to set the tank pressure.

I.brought.It.to.use.The tanks for a receiver, but the compressor.part is.soo cool I'm thinking about putting a 5hp stationary motor on it and having it as a back up to my diesel compressor.

[CaMpylobacter]

Thanks guys! Thats exactly what i was wanting to know!

Hadnt thought about unloader valve (and non return)- good points. Time to mash ali express

 

that wabco one I roll is unloader and check valve all in one. ideal Neil.

[datlow]

Standard ones are called a pilot unloader valve, many different brands & styles just find one with the thread and ports where you want it

1/2 good for 30 ish cfm,

chinese looking copies on eBay can't seem to find them on Ali app

http://www.ebay.com/itm/GAS-AIR-COMPRESSOR-PILOT-CHECK-VALVE-COMBO-140-175-PSI-/280520913228

Some come with port for throttle, handy if they also have a port at the intake, can chuck a ball valve into that and open it to make pull starting easy under load (just vents pump to atmosphere)

[nickrock]

Or you could do like what I have done and have a couple of extra cheap electric compressors under the bench which I plug in to the big tank I have when I need a bit extra

Will run a high volume spray gun full time but my big old 3/4 rattle gun will get a couple of stubborn truck wheel nuts off before I need to let it catch up but that rattle gun is real old school and just hogs the air it was second hand when I brought it 40 years ago