Daisy chaining compressors

[Tai Fu]

Does anyone do that to get extra CFM? I have seen tradesmen in Taiwan daisy chain several direct drive compressors so they wouldn't have to carry a heavy 2/3 HP compressor up a narrow flight of stair when they need to use framing nailers or spray paints.

I just received a 2HP belt drive cast iron compressor... and man my back hurts after having to move that up 3 flights of stairs by myself. However in the event that I might need extra CFM, but not wanting to move 1000lb compressor, would it be wise to daisy chain several compressors together to meet the required CFM? I've even seen this done at factories where for whatever reason, they'd have several 10HP compressors rather than one 30-50HP compressor...

[Mike Henderson]

The term "Daisy Chain" would normally apply to taking the output of one compressor and running it to the input of the next compressor. I doubt if that's what you want to do. What you probably want to do is gang the output of several compressors together so that they are all supplying the work.

I never done that but I don't see why it wouldn't work.

Mike

[Tai Fu]

Although I often wonder if that's even possible, taking the output of one compressor and send it into the input of another... maybe that could create a multi stage compressor to compress air to like 1000000 psi

[Dave Cullen]

I imagine you're talking about paralleling compressors into a common output. I suppose two compressors in parallel should combine their CFM capacity (kinda makes sense), but I've never tried it.

I have seen automotive painters put an auxiliary tank on a too-small compressor to give more capacity in the short term. Like if a spray gun empties the tank before you're done spraying a panel then adding more air storage gives you more time before the compressor is called upon to keep up. Of course it takes longer to refill with the extra tank, but painting typically is not 100% duty cycle.

[John TenEyck]

We had two compressors at work feeding one chiller and receiver. We could run either one alone, or both together, as required to meet the flow demands. As long as the regulator from your receiver, or manifold, is set no higher than the turn-on pressure of the compressors it should work fine, and you should get close to the combined flow of the compressors in the system as long as the piping is large enough to allow for that flow.

John

[Matt Meiser]

I really can't see your compressor caring whether the pressure its compressing against was produced by itself or another pump. Most industrial facilities have multiple compressors in parallel--sometimes many thousands of HP.

[Greg R Bradley]

I have a 25hp IR Screw Compressor at one end of the line and 50hp IR Screw Compressor + 15hp IR piston compressor at the other end. Based upon expected need that day, we turn on 25hp or 50hp Screw compressor, which run continuously. Then the 15hp piston compressor will cycle on if, or when, needed.


277464

[Matt Meiser]

Cute little baby ones :)

One of my customers will typically have on the order of 6-7 ranging 500-1500 HP at a plant--usually IR.

[Greg R Bradley]

Very glad I don't have to pay the electric bill to run those.........

[Ben Burns]

I have connected 2 150 psi compressors together to get additional Cfm. It worked well. You have to have high enough of a usage that when one compessor kicks on the pressure keeps dropping until the other kicks on. They never are totally synced. I did this to run a small sandblaster. I kept both compressors regulators wide open and regulated it at the sandblaster.

[Michael W. Clark]

Cute little baby ones :)

One of my customers will typically have on the order of 6-7 ranging 500-1500 HP at a plant--usually IR.

That's a good one. I worked in a low pressure die casting shop where we had about 10,000 CFM in each of two different compressor rooms, no motors that big though. One foundry I worked at had a couple of large Joy compressors though. All the compressors were parralleled and the controls is always the issue. You want all of them fully loaded, and one trimming. Rarely works that way without an expert setting up controls for it.

[Larry Edgerton]

I tried it once and could not make it work. I'm sure there is a way, but my attempt failed. I ran both outputs to a Tee, one line to a spray gun. One compressor would not shut off, not sure why. As long as I was spraying it was fine but as soon as I was done I had to unplug the compressor that wanted to run on.

I hauled a big compressor to a site this week and was wondering again what caused this.

Larry

[Greg R Bradley]

Larry,
If both compressors are conventional compressors that cycle on and off, they will need to be compatible on the pressure settings where they start and stop. You may want to have a valve on each output before the tee fitting until you get them adjusted. I prefer to adjust them both to be the same and then adjust one down around 5psi from there.

You also need to make sure each has a one-way valve between the compressor unit and the tank of that unit and that they work correctly.

Did the one that continued to run keep moving air backwards thru the unit that had cycled off?

[Jason Roehl]

Although I often wonder if that's even possible, taking the output of one compressor and send it into the input of another... maybe that could create a multi stage compressor to compress air to like 1000000 psi

In theory, this might work, however, the limiting factor will be the failure pressure of the components beyond the first compressor. More than likely, the valve seals in the second compressor won't be able to handle a pressure much higher than what the first compressor outputs. And, if they did, then the tank on the second compressor becomes a dangerous bomb (provided you had changed out the pressure switches on the second compressor to higher pressure cut-in/out ratings).

[Lee Schierer]

It is very common in industrial settings to have multiple compressors feeding a factory. We had huge compressors when I worked at Channellock that supplied the air for the forging hammers. There were three of them feeding into on very large accumulator and they were set to run such that when the pressure dropped due to demand, one then the next would cut in to provide more volume of air.

[Jim Neeley]

Installing two identical compressors in parallel is a no-brainer; just do it.

Likewise, installing two different compressors with the same maximum pressure rating is a no-brainer.

Where the complexity can come in is if you have one compressor rated at 175psi and another rated at 110 or 125. In that case you can install a regulator on the discharge of the high pressure compressor, setting it down around the pressure of the lower pressure unit. Filure to do so may cause the HP compressure to overpressure the LP unit, causing the relief valve on that compressor to pop.

Just my $0.02.. YMMV.

Jim

[Mike Cutler]

Does anyone do that to get extra CFM? I have seen tradesmen in Taiwan daisy chain several direct drive compressors so they wouldn't have to carry a heavy 2/3 HP compressor up a narrow flight of stair when they need to use framing nailers or spray paints.

I just received a 2HP belt drive cast iron compressor... and man my back hurts after having to move that up 3 flights of stairs by myself. However in the event that I might need extra CFM, but not wanting to move 1000lb compressor, would it be wise to daisy chain several compressors together to meet the required CFM? I've even seen this done at factories where for whatever reason, they'd have several 10HP compressors rather than one 30-50HP compressor...

Tai Fu
As stated they aren't daisy chained, but paralleled, which is common, world wide application. The difference is that they are configured for a "lead/lag" strategy
Will the CFM be additive? Doubtful, but you will increase the CFM on the common discharge header. The variables will be all of the ID's of typing, piping and hose involved.
It's not exotic, or complicated at all. Put two compressors in parallel, set the regulators as close as you can to the same cut in and cut out points, and give it a whirl. You may have to increase the regulated pressure to the point that both compressors are in continuous run, so that you don't have a square wave pressure output signature on your common header.
You shouldn't need discharge flow checks on the compressor outlets with small compressors, The regulator discharge is downstream sensed and will close against an increased downstream pressure. If they were big industrials, than yes, there are discharge flow checks.

One of the reason tat you see multiple smaller units in industrial applications is for a myriad of reasons.
1.) Redundancy. You have backups in place of you lose a compressor.
2.) Available power, electrical distribution. The electrical system may support multiple smaller units, but no single large units without expensive upgrades to wiring and power feeds. I have 5 at work, the smallest being 85 HP, in addition to two non filtered units, and we can crosstie to another facility and have even more standbys at the ready. We've hooked up as many as 40 of the portable diesel powered Atlas Copco's, in parallel. it's quite the little "Air Farm" when we do it. 3" hoses everywhere.

Point is, yes it's done all the time.

[Jeff Erbele]

Will the CFM be additive? Doubtful, but you will increase the CFM on the common discharge header.


The question and the statement are in direct conflict.
With multiple compressors in parallel:
* CFM is cumulative. That is the point of creating a manifold, increase the volume. Having restrictions such as airlines to small to deliver the available CFM is counter productive.
* PSI is not cumulative. It cannot exceed whatever the setting is of the pressure switch with the highest setting. Well, if everything is functioning properly.

My cousin had a small compressor, probably a 1 HP, single stage, 20 gal in his corrugated steel quonset. The pressure switch malfunctioned and it pumped until it blew up the tank. The tank was rolled steel in the middle as many are, with two dome shaped caps welded on each end. When it blew up, it mostly unrolled the steel back to a flat sheet, with one end partially attached and blew the other end across the shop. A full 5 gallon pail of grease, with lid clipped in place caught the brunt of the force; popped the top off of that, flattened that pail and with much of the grease on the ceiling, a fair amount fell back to the shop floor and splatter every direction. Parts of the compressor went thru the steel roof.

Lucky, no one was in the shop at the time. We will never know but always wondered what PSI was attained before the explosion.

[Mike Cutler]

Jeff

Maybe I wrote is incorrectly.
The discharge header output flow of each compressor will be close to it's rated value, butat the point the the individual compressor discharge headers are joined, via manifold, or tee, at that point the common discharge header, or the header that sees all of the cumulative flow, will not be additive. It will be close, if the common header is sized appropriately, but it's not like hooking up three, 3 cfm rated compressors ,will result in 9 cdm total flow at the discharge of the common header. More consideration would need to be given. PSI on the common discharge header will be a function of each individual compressors ability to maintain a flow rate at a given pressure. When not in in use the pressure on the discharge header and all the commons in absence of individual discharge flow checks will reach stasis and reflect the pressure , "reset" set point of the highest individual compressor regulated output setting.

As for your cousin's compressor; It sounds like a few things were missing. There should have been a tank pressure relief valve, and a discharge pressure relief valve, built into the compressor, usually it's just a small disc that blows. Large air receivers not only have reliefs, but they have designated blow out ports welded into them. Definitely, someone would have been hurt, or worse, if they'd been in the room when it blew the tank.
I've been setting up and tuning multiple large compressor arrangements for 30 + years now, and you definitely need to respect the energy involved, even in a small portable compressor.