Linking or coupling compressors

[richweld]

I’ve read it is possible to link or couple up compressors, but I need some advice as to (1) how to set them up to avoid exceeding duty cycles, and (2) what output pressure settings should I use on the 2 compressors to avoid any problems.

I have 2 compressors:-

Clarke 3 HP (indirect drive), 14 cfm air displacement, 50 litre tank, max pressure 10.3 bar, cut in pressure approx 8 bar.

Wolf Air 2.5HP (direct drive), 9.5 cfm air displacement, 24 litre tank, max pressure 8 bar, cut in pressure approx 6 bar, duty cycle 50% and continuous running should not exceed 15 minutes.

The Clarke is OK to run my air tools and spray gun. Bought the Wolf to run an air fed mask, but find it has a 50% duty cycle and continuous running limit of 15 minutes.

I’m thinking of coupling up the compressors to run them into a single fixed copper line similar to what Malcolm has done here at post number 3:-

http://www.mig-welding.co.uk/forum/showthread.php?t=5816

What I’m unsure about is how to set up the outlet pressures of the compressors to avoid the Wolf from continuously running.

 

[rtbcomp]

Trial and error really, it depends how much air you'll be using. Set the Wolf pressure lower than the Clarke so it cuts out first.

 

[richweld]

Just noticed that Malcolm has connected his 2 compresssors into the fixed coper line direct from the tanks, not from the regulator outlet of the compressors.

http://www.mig-welding.co.uk/forum/attachment.php?attachmentid=3349&d=1209317645

So the tank cut in pressures would determine when the compressors run.

As the Wolf has a lower cut in pressure, wouldn't this mean that it will start up before the Clarke and thus risk exceeding duty cycle. Or am I misunderstanding things?

 

[rtbcomp]

The pressure in each tank will be the same, so the setting on each compressor switch will determine when that compressor cuts in or out. If the Wolf is set to cut out at 9 bar and the Clarke to 10, the Wolf will cut out at 9, the Clarke will continue to run, pressurising both tanks, until 10 bar is reached.

If there is 1 bar hysteresis, the Clarke will cut in at 9 and the the Wolf at 8 so the Wolf will run less.

 

[richweld]

Thanks. This is becoming clearer now.

I can understand that the pressure would be the same in both tanks where the compressor tanks are directly connected to the fixed copper line (as in Malcolm’s photo of his set up), but would that hold true if the compressors are connected to the fixed copper line via the regulated outlets of each compressor?

eg. If I set the regulator on the Clarke at say 9 bar and the regulator on the Wolf at 7 bar, would the Clarke try and pressurise the Wolf’s tank to 9 bar or would the regulator set at 7 bar prevent it from doing so?

I cannot connect the 2 compressors directly from the tanks (as in Malcolm’s photo of his set up) because the max pressure on the Wolf is 8 bar. When the pressure in the Clarke starts to rise above 8 bar, the safety valve (blow off valve) on the Wolf should cut in and release the pressure.

On my set up, I think I will have to connect the compressors to the fixed copper line via the regulated outlets of each compressor, and limit the outlet pressure on the Clarke to a max of 8 bar.

Does this make sense? I just want to sort this out on paper before I start to fix any copper pipe.

 

[rtbcomp]

That might work but I'm not sure how a regulator will behave under back-pressure. You could fit a non-return valve in the output of the Wolf.

8 bar (app. 112 psi) is about the normal pressure for an air-line anyway, 10 bar is a bit on the high side so I'd drop the Clarke down to 8 bar at the pressure switch. Have the two compressor switch at slightly different pressures to avoid mains surges.