Brand of compressor switches with separate hi-low adjusters

[rcx132]

Seems most compressor pressure switches have just the one adjustor which adjusts both the hi and low psi. I've got two compressors connected together so it means the big one is doing all the work, the small one only kicks in at 85psi.

Anyone know a brand of compressor switches that still has adjustable hi and low? Or some of them had a single adjustor plus a differential adjuster, that would also work.

 

[rtbcomp]

By Hi and Low do you mean switch-off and switch-on pressures? The cheap ones these days seem to have a fixed differential of about 30 psi, older ones have a differential setting, usually marked by a triangle (Delta) symbol.

I don't see a problem with one compressor doing most of the work, if you reduce the differential on a compressor it will switch on/off more frequently, using more electricity and causing more wear & tear and possible overheating on the motor. You need to have them set to switch at different pressures to prevent the mains surge if they both came on at the same time.

 

[Seadog]

These are the type fitted to Hydrovane compressors - http://www.condor-druckschalter.de/produkte/mdr5/html/mdr5.html

 

[Burdekin]

As above. If one is adequate to supply the air then no issue, if you are using more air than one can supply then the pressure will drop and the second compressor will kick in.

If you want to run them at the same time you could wire to the one switch, but you'd need to ensure your electrics are up to it.

 

[rtbcomp]

If you want to run them at the same time you could wire to the one switch, but you'd need to ensure your electrics are up to it.

Put a time delay in so there is a pause before the 2nd one starts up, but you've got the added complication of controlling both unloading valves with one switch.

 

[RaceDiagnostics]

I have both of my compressors connected to the switch on the first one, the standard switches are rated up to 20A.

 

[knighty]

I'd be tempted to have the smaller compressor kick in sooner and run to a higher pressure than the larger one.... rather have the small one running for long periods that both/either going on/off all day

extra air capacity from having both tanks connected together should reduce/negate any problems you'd have to constant stopping/starting ?

 

[rtbcomp]

I have both of my compressors connected to the switch on the first one, the standard switches are rated up to 20A.

How do you operate the unloading valve on the 2nd one?

extra air capacity from having both tanks connected together should reduce/negate any problems you'd have to constant stopping/starting ?

Don't think it would make any practical difference - a larger tank reduces the on/off cycles, but with 2 tanks connected you've got 2 pumps filling them.

It all depends on pump capacity, tank size, operating pressures, air demand.

I had a 2hp and a 3hp connected together operating through their own switches set to come on about 10psi apart. They were 20 feet apart, and supplied me with all the air I needed. I had the larger one cutting out at a lower pressure simply to keep the noise down as the neighbours could hear it. They both ran constantly while I was blasting, it's only when I stopped that the big one cut out and the little one carried on until both tanks were full.

 

[RaceDiagnostics]

How do you operate the unloading valve on the 2nd one?

Looks like a I need some educating here, whats an unloading valve and what does it do as I haven't done anything with it?

 

[rtbcomp]

^^ It's situated in the pressure switch and unloads the pipe between the tank and the pump (the delivery pipe), giving the "hiss" you hear when the motor stops. The idea is to vent the pipe to atmosphere so that when the motor restarts it doesn't have any load on it.

If you're running 2 pumps off one switch the unloading valve will only operate on the pump with the switch, as it's opened mechanically when the switch opens. If the pumps operate simultaneously you could connect the thin pipes that connect the non-return valve to the unloading valve together so both delivery pipes exhaust at the same time.

 

[rtbcomp]

View media item 1676

 

[knighty]

extra air capacity from having both tanks connected together should reduce/negate any problems you'd have to constant stopping/starting ?

Don't think it would make any practical difference - a larger tank reduces the on/off cycles, but with 2 tanks connected you've got 2 pumps filling them

(pulling numbers out of the air but...)

if the smaller one was setup to kick in at 110 and out at 120

the larger set to kick in at 80 and out at 110


then the smaller one should do most of the work, normally 110/120 on/off would be too tight and the pump would short cycle turning on and off all the time.... but with the extra air capacity of the large tank it shouldn't short cycle, it'll take a while to fill both tanks to full

(also, large compressor probably has a large tank, which helps even more?)


if lower pressure is acceptable I'd set the larger ones kick in pressure even lower, I'd rather have the small one running for long periods than have the large one stopping and starting

 

[rtbcomp]

... I'd rather have the small one running for long periods than have the large one stopping and starting

IIRC the optimum is a 50% duty cycle over 30 mins (15 on, 15 off)

 

[RaceDiagnostics]

^^ It's situated in the pressure switch and unloads the pipe between the tank and the pump (the delivery pipe), giving the "hiss" you hear when the motor stops. The idea is to vent the pipe to atmosphere so that when the motor restarts it doesn't have any load on it.

If you're running 2 pumps off one switch the unloading valve will only operate on the pump with the switch, as it's opened mechanically when the switch opens. If the pumps operate simultaneously you could connect the thin pipes that connect the non-return valve to the unloading valve together so both delivery pipes exhaust at the same time.

So that means I'm putting unnecessary strain on the electric motor/pump each time it restarts?

 

[rtbcomp]

^^ Assuming of course you have the conventional piston compressors, yes.