# Automatic Switching of Lead Compressor



## PaulMJohnson

Hi,

I have a few sites where I have multiple (upto three) compressors all connected to the same system. Typically they are not the same model or capacity compressors.

The problem I am experiencing is that I'm ending up with one compressor that runs pretty much all the time, and the second barely at all. I'm ending up seeing reliability problems with the second compressor as it is not used enough.

What I'm wondering is, is there some device I can use to control which compressor is in the lead? I know I can set the load/unload pressures differently for each compressor, which is effectively what I have done, but that means one compressor barely ever turns on, as the largest compressor is set to load first and most of the time meets the air requirements.

What I'm looking for is some sort of a timer that could switch which compressor leads.

I'm using various Atlas Copco compressors.

Any help would be appreciated. As you can probably tell, I'm no expert in these matters!

Thanks.


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## 89yt12

it depends on what kind of switching system you want ...... a water heater timer would work if you are wanting to use time as a basis, it would be in line with the power to the unit


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## PaulMJohnson

The problem with something like that is it would completely turn one of the compressors off. What I want to switch is which compressor is in the lead.

Effectively with a two compressor system, I have one of them set to load at 115psi. and to unload at 125psi, whereas the second I have set to load at 105psi, and to unload at 125psi.

The problem is, the one set to load at 105psi hardly ever turns on, as the one that loads at 115psi normally has enough capacity to meet demand.

What I want to be able to do is have, for example on day 1, compressor 1 loads at 115psi and compressor 2 loads at 105psi, then on day 2, compressor 1 loads at 105psi and compressor 2 loads at 115psi.


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## 89yt12

with out adjusting a pressure switch everyday, im not sure wjat else could be done 

i hope someone else will chime in


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## Ironmower

Use only one pressure switch, or two the same range??


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## SonnyT

Not sure about Atlas Copco, but Ingersoll Rands you can do that with, but you have to buy a program standalone interface and then it controls the compressors. Might get hold of Atlas and see what they have. It wouldn't be cheap.


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## PaulMJohnson

Thanks for all the input everyone.

Sonny T, I think you've hit the nail on the head. I have heard of such things, but have been desperately hoping to find a third party "off the shelf" solution, since my experience with Atlas Copco has been very poor, and ideally I'd prefer to not have anything more to do with them.

I'll give them a call though. I'm not too concerned about the cost (within reason). I'm looking at 150+ compressors across 56 sites for this problem, and in a lot of my locations I'm seeing perfectly good compressors having all manner of reliability problems merely because they are not getting used enough.

Thanks for all the help guys - this is a great and friendly forum. Not what you always find on the internet!


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## 89yt12

PaulMJohnson said:


> Thanks for all the input everyone.
> 
> Sonny T, I think you've hit the nail on the head. I have heard of such things, but have been desperately hoping to find a third party "off the shelf" solution, since my experience with Atlas Copco has been very poor, and ideally I'd prefer to not have anything more to do with them.
> 
> I'll give them a call though. I'm not too concerned about the cost (within reason). I'm looking at 150+ compressors across 56 sites for this problem, and in a lot of my locations I'm seeing perfectly good compressors having all manner of reliability problems merely because they are not getting used enough.
> 
> Thanks for all the help guys - this is a great and friendly forum. Not what you always find on the internet!


 
glad someone could help you out , tell a friend about us


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## 89yt12

I PMed another member that may be able to help you out more, hopefully he can post up soon


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## Roadlizard7

I'm much better on mechanical equipment than on controls and electrics and electronics, so I'm going to have to talk to some of my engineers to find out how to do it. I know there's a way, because that's what they do with duplex compressor packages to even out the usage on both units, but I'll be darned if I can remember how it's done. I'll get back in a day or so.


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## Roadlizard7

One way you could get them both to run often is to set the smaller compressor to load first, and when it cannot handle the load (probably fairly often) then the larger compressor will kick in until the load can be handled. However, that will keep the smaller compressor running most all the time. 

But I'll still check on a control solution. It might require a microprocessor control that you program to do what you want.


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## PaulMJohnson

Roadlizard7 said:


> One way you could get them both to run often is to set the smaller compressor to load first, and when it cannot handle the load (probably fairly often) then the larger compressor will kick in until the load can be handled. However, that will keep the smaller compressor running most all the time.
> 
> But I'll still check on a control solution. It might require a microprocessor control that you program to do what you want.


Hi!

Thanks for the ideas - I actually tried setting the smaller one to load first, and as you say, I end up with the smaller one loaded all the time.

That I could live with, but it lead to the bigger compressor cutting in for such a short period of time, it was causing reliability problems on the big compressor!

The thing is, the way my facilities run, we pull a lot of air for about 4 hours in the morning, then things are much reduced for the rest of the day, so what I'm wanting is to get to a point whereby at least every other day, the smaller compressor is in the lead for the non-peak hours, so that it can do most of the work for the rest of the day when our capacity requirements are much lower.


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## Ironmower

wouldn't be automatic, but why wouldn't a 2-way switch work? Just flip it everymorning??


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## Roadlizard7

I checked with my engineers, and they said they sat down with an electrician and designed a little control in a box to do that on a duplex system. They also said that just about any good electrician could design a control to do what you wanted. You pay him to design it once, then just copy it for all your other locations.


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