Controlling a petrol compressor?

[gerrymoore]

I've carried this over from the plasma cutting thread. (might be worth reading it for the pictures etc.)
Basically, I have a 5.5hp Honda powered compressor that has no auto idle or cut off when pressure is reached. I've always just kept an eye out and never let it go over 110psi when I'm using my plasma CNC.

However it seems you can get something like this

https://www.zoro.com/cdi-control-de...ssor-throttle-control-tc63-4ka000/i/G2547797/

To have the motor idle when a set pressure is released. There's a similar set up called a bullwhip in the USA.

Anyone know if/where you can get these things in the UK as all the ones I find on Amazon or Ebay are either USA ship only or horrendous postages.

 

[Keith 66]

I have a petrol compressor it has a 6hp Kohler engine on it driving a three cylinder AIE pump, it has a simple unloader valve, it runs at constant speed & as soon as the set maximum pressure is reached it blows off & dumps the air from the pump before it goes into the tank.
I would think a throttle based set up would be more trouble as the motor would be likely to stall?

 

[rtbcomp]

Reading the blurb looks like it's designed to be used in conjunction with something like this https://www.machinemart.co.uk/p/1-2in-pressure-unloader/

As soon as it unloads the engine drops to idle. It shouldn't stall as the delivery pipe will be venting the pump to atmosphere.

If the pressure doesn't build up anyway under current use I'd just fit the unloader and save the cost of the throttle control.

 

[bogbushcricket]

Could one of these be adapted to do the job?

http://www.ebay.co.uk/itm/Festo-pne...398120?hash=item33cc44e0a8:g:qRQAAOSwhQhY7GY1

 

[rtbcomp]

^^ As long as they don't block the air coming out of the unloader

 

[gaz1]

from your link this is 100psi

https://www.zoro.com/conrader-throttle-control-gas-engine-drivn-100psi-tcxlpw-48/i/G5255634/

to do this

 

[gerrymoore]

Hi RTB..this is already fitted to my compressor..it's a Facciotti AU77 but I have no idea how to set it? In the 5 years I've been using the compressor it has never 'unloaded' to my knowledge as I've never let it go over 110 psi...and have no need to go any higher.

Now that I've seen this method of switching the motor to idle I quite fancy having a go but only if it doesn't cost too much!

Would the little air tube be where I would fit a piston/valve?? And I presume the plated bolt is the adjuster for the pressure??

I'm presuming the brass tube to the right is a safety prv?

 

[bogbushcricket]

^^ As long as they don't block the air coming out of the unloader

I would have thought that when the unloader trips it would send tank pressure down the plastic tube and vent pump air to atmosphere through the cone shaped brass filter on the left of the valve in Gerry's pic above.

But I could be wrong

 

[rtbcomp]

The bit to the right is the pressure relief valve, I would guess 11 bar (10 bar working pressure)

I would guess the plated bolt is the adjustment, screw out to decrease the operating pressure.

The blocked off plastic tube would normally go to the unloading valve on a pressure switch, it will be at delivery pipe (the pipe between the pump and the valve on the tank) pressure. It will empty the delivery pipe but not the tank as it's on the input side of the valve in the unloader.

I would connect the throttle control to that plastic pipe, so that when the pressure drops due to the unloader opening the engine throttles back. When the unloader closes pressure will build up in the delivery pipe and the throttle will open.

Those rams mentioned above might work, but you'd need a spring return.

 

[gerrymoore]

Great..thanks for the information..I've written to a supplier in the USA to check shipping costs but would have thought something similar should be available in the UK..I might try ringing a couple of petrol compressor UK suppliers.

 

[rtbcomp]

Ask them how it works, does it open or close the throttle when pressure is applied?

 

[rtbcomp]

Is the engine governed? If so I wouldn't bother with controlling the throttle. Once load is taken off the engine by the unloader opening it will try to speed up but the governer will maintain the rpm. Although the engine will be running at the same speed it will use less fuel as it will be running light. As it will be running at speed it will be less likely to stall when the unloader closes.

 

[normspanners]

http://www.ebay.co.uk/itm/Bore-10mm-Stroke-30mm-Double-Acting-Mini-Pneumatic-Air-Cylinder-CNBTR/191913446625?_trksid=p2385738.c100677.m4598&_trkparms=aid=222007&algo=SIC.MBE&ao=1&asc=20160908110712&meid=e47ba4931a1a499093e1b43ae1246327&pid=100677&rk=10&rkt=50&sd=191913469359
something like this might work attached to spring so the ram is pulled out by the spring when operated would pull the throttle back against the governor spring to idle and cheap enough .
There should be no problem with the engine, as mine runs at idle when not a lot of air is required and the unloader cuts in and out with no problem. just hear the governor open a little.
starting it can be a bind though, really need the unloaders to have a manual over ride like their bigger brothers.

 

[Keith 66]

Is the engine governed? If so I wouldn't bother with controlling the throttle. Once load is taken off the engine by the unloader opening it will try to speed up but the governer will maintain the rpm. Although the engine will be running at the same speed it will use less fuel as it will be running light. As it will be running at speed it will be less likely to stall when the unloader closes.

This is what mine does, once you start it you move the throttle to run (it has a nice icon of a rabbit at speed) & the govenor keeps it at constant rpm. I havent noticed it drinking less fuel though, those Kohlers are reliable but do like to drink!

 

[8ob]

How about an electro magnetic clutch robbed off an old air con pump fitted to the engine and wired up to a pressure switch? Probably use a lot less fuel when not on demand if the pump is static. Just a thought.

Bob