Linking 2 compressors

[AHTI123]

Ive got 2 of exactly the same compressors and have linked them together but they are not sharing the work, one is particularly lazy with the other doing most of the work.
I have pipework coming out of each with a non-return valve in each pipe, before they tee together.
What have I done wrong?

Thanks.

 

[Morrisman]

Unless you use enough air to trip both into running one will always lag behind the other. The low pressure switches won't be set exactly the same, thus one will always come on before the other, and run for longer.

 

[MetalMonkey]

You could adjust the pressure switches to even them out a bit more, but in reality having them switch on at slightly different pressures is a good thing as it balances out the surge from the motors starting.

If most of your air consumption is quite light and easily satisfied by one compressor you could spread use between the machines by periodically turning off the "eager" one to force the other one on and just round robin them - only turning both on when you really need the extra capacity.

 

[RaceDiagnostics]

I wired the pressure switch of one compressor to power both pumps, just check that it's rated high enough.

 

[AHTI123]

Thanks for the replies so far.
I was using it yesterday and when i say one was lazy it didnt come on at all, except when i turned the dominant one off to give it a break. But the tool i am using needs a lot of air otherwise one compressor would nearly run flat out - (but not quite.)
The compressors are 3hp 150ltr each.

Interested in what @RaceDiagnostics has said if that would sort the issue out once and for all?

 

[mtt.tr]

This commercially is dealt with by controllers.

I know hpc (that's what I was trained on) were ethernet connected one slaves and the other is the master. Then they switch.

Or you have wall mount controller.
Or you manually change the pressure switch settings.

 

[not done it yet]

Unless you use enough air to trip both into running one will always lag behind the other. The low pressure switches won't be set exactly the same, thus one will always come on before the other, and run for longer.

Thanks for the replies so far.
I was using it yesterday and when i say one was lazy it didnt come on at all, except when i turned the dominant one off to give it a break. But the tool i am using needs a lot of air otherwise one compressor would nearly run flat out - (but not quite.)
The compressors are 3hp 150ltr each.

Interested in what @RaceDiagnostics has said if that would sort the issue out once and for all?

Clearly(?)the ‘lazy’ one would only switch on at a lower pressure - and that lower pressure will never be reached unless you are exceeding the volume delivered by the one running. Seems like you never, or rarely, require two compressors?

 

[Erie Fred]

Best to have both running and actually filling the tank so they can turn off for a break before both kicking in again rather than running one flat out

"For a break" ???
Running an air compressor for a long time is good, get's the oil up to temp, boils off condensation.
Stopping & starting is harder.

 

[Morrisman]

Best to have both running and actually filling the tank so they can turn off for a break before both kicking in again rather than running one flat out

You could link the electricals together to make them both run simultaneously.

 

[mtt.tr]

One suggestion then

2x pressure switches one set to switch back on lower than the other (differential)

These can go through a rotating switch used to divert which compressor is the lead and which one lags.

Every day switch it over.

 

[Erie Fred]

Yes for a break????????
My single phase compressor's have a 50% duty cycle

Get a bigger motor.
If your going to sandblast, you need 100%

 

[AHTI123]

Yeah, compressor definately doesn't want to be running constantly - if it does (and this is the problem with only one compressor running) the thermal cutout will pop, and needs to cool down.
Il go back through the comments later to clarify in my mind but thanks for responses.

 

[brightspark]

Get a bigger motor.
If your going to sandblast, you need 100%

that wont help its the pumps that cant handle the duty cycle. i nearly cook my twin pump and motor setup after running it for 20 minutes im not realy bothered though if it jacks in hard luck didnt pay a lot for it

 

[Erie Fred]

that wont help its the pumps that cant handle the duty cycle. i nearly cook my twin pump and motor setup after running it for 20 minutes im not realy bothered though if it jacks in hard luck didnt pay a lot for it

What kind of homeshop crappy air compressors are Y'all running ?

 

[roofman]

What kind of homeshop crappy air compressors are Y'all running ?

I have 2 x 150L (3hp each) running staged, pressure drops below 60 psi and the 2nd one kicks in. under the bench out the way.

 

[mtt.tr]

I have 2 x 150L (3hp each) running staged, pressure drops below 60 psi and the 2nd one kicks in. under the bench out the way.

View attachment 421694

What sort of workshop is that. Room to navigate no piles of junk.

Oh my shame, why realise my shame.

 

[brightspark]

What kind of homeshop crappy air compressors are Y'all running ?

apart from a homemade 14cfm compressor made from a wagon compressor that has run for 55 years and still runs the twin pump setup and a roadtow comp that is 1945 and in good condition and starts 1st time everytime have you anything better

 

[Erie Fred]

that wont help its the pumps that cant handle the duty cycle. i nearly cook my twin pump and motor setup after running it for 20 minutes im not realy bothered though if it jacks in hard luck didnt pay a lot for it

apart from a homemade 14cfm compressor made from a wagon compressor that has run for 55 years and still runs the twin pump setup and a roadtow comp that is 1945 and in good condition and starts 1st time everytime have you anything better

View attachment 421697

So these (2) machines you post are not the same. Only the tiny electric one overheats.

I have 6 compressors up to 200 cfm, and none, even the cheapest Harbor freight electric (3 hp)
have to stop for cooling. Routinely blast using one of my 2 DIY cabinets for hours at a time, 3 pots
for outside usage.
Mostly outside these days using a 1/8" nozzle on my 10 hp Quincy electric. 300-600 lbs of sand is a routine job.

The 200 CFM is driven by my tractor PTO and I've run a 3/8" nozzle on the large pot (300 lb Clemco
pot with remotes) I did 12k lbs of coal ash one year with that set-up.

 

[Morrisman]

that wont help its the pumps that cant handle the duty cycle. i nearly cook my twin pump and motor setup after running it for 20 minutes im not realy bothered though if it jacks in hard luck didnt pay a lot for it

I put an electric fan on my small compressor when I was spraying with it, to keep it cool. I was living in the tropics at the time, and it never overheated even running non stop for a half hour or more.

 

[MetalMonkey]

I have 6 compressors up to 200 cfm, and none, even the cheapest Harbor freight electric (3 hp)
have to stop for cooling.

I'm fairly sure the 3HP generic Chinese pump compressors are pretty much the same either side of the pond, just perhaps ours run on 220v.

Here is a UK one - rated at 70% duty cycle
https://www.pssi.co.uk/product/erp-a18-150-240v/

And another, rated at 50% on 13A and 89% on 16A
https://surreyweldingsupplies.co.uk/hyundai-3hp-100l-belt-driven-compressor---hy3100p-16076-p.asp

Here is a US one - rated at 50% duty cycle
https://www.compressed-air-systems.com/recip/com-elec/port-3-elec.html

Can't find any mention of a duty cycle for harbour freight compressors - but that doesn't mean it doesn't have one, just that they haven't said.

Over here typically 3hp is going to be about the biggest you will get from single phase supply as it will run from a UK 13A plug, or a 16A commando.
You do get the odd 4hp single phase unit which needs a bigger supply. Or they will go for a tandem dual 3hp unit instead.

Much above that and you are into three phase industrial compressors, or screws or hydrovanes - which is an entirely different ballgame.