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I have two air compressors with about 8 bar max. pressure and 150 liters per minute output at 2 bars.

Now I need min. 220 liters per minute at 2 bars and think I need to connect the two compressors together.

I've found several instructions on the internet how to do this but nobody is talking about possible problems (except when the pressure is very different or a single circuit isn't capable of handling the required current).

For the connection, I would use an air hose Y connector with two male and one female plug.

So, assuming

  • both compressors are on the same pressure, and
  • the circuit is capable of handling the required current,

are there any other problems or dangers I might encounter?

ThreePhaseEel
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marsh-wiggle
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  • Alternative solution - hire a larger compressor for this job, if its a one-off. – Criggie May 30 '22 at 01:22
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    @Criggie, I already checked that. This job will last about 4 weeks and hiring the compressor is more expensive than good used large 400V compressor. One option I think about is to buy such a compressor and sell it after the work is done. – marsh-wiggle May 30 '22 at 05:28
  • I'd suggest that if you are possibly in the market for a big, used compressor, others will be too, and that this might be a good option. i.e. you'll get what you need and still be able to sell it when you're done and not be "stuck" with it. Of course, if you use air tools, there's always a good use for more CFM... – FreeMan May 30 '22 at 13:20

4 Answers4

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Just parallel them

This will work fine as long as the compressors are reasonably close in pressure rating (bar, atm, kPA or PSI).

It is vital they be reasonably close, because both/all tanks will equalize pressure at the highest compressor's setting! You cannot couple a 10 bar compressor with a 2 bar compressor, because the 2 bar compressor probably has a tank rated for 3 bar, which means at 8-9 bar it is likely to explode like a grenade.

Compressors already have check valves in them, that are designed to work at their rating. As long as the compressors are reasonably matched that is fine.

Realistically what is going to happen is that one of the compressors will run most of the time, and the second will kick on when load is heavy. That is fine, and is to be expected. That is because one compressor's setting is slightly higher than the other. There is no way to make them equal.

Get it straight about fuses!!!!

or the fuses too weak to run both on one circuit

NO! Fuses are not "weak"! That is wrong thinking!

Fuses protect the wires inside the walls. The wire can only handle so much current (amps) before getting too hot and starting a fire. Never enlarge a fuse.

The fact is, the wires are weak. Upgrade the wires. Have an electrician install additional circuits to power your extra things. (or sometimes, a larger circuit). Then you will also have more or larger fuses obviously.

Use the fuse that is correct for the wire. Never enlarge a fuse.

Harper - Reinstate Monica
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    Thanks for your help. Luckily I have enough circuits with their own fuses. So I won't have this problem. – marsh-wiggle May 30 '22 at 05:30
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    Who said "I don't care about a fire inside the wall"? – user253751 May 30 '22 at 08:53
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    @user253751 I assumed that "weak" implied that something needs to be improved here. Sorry for my bad English. Is there a better word here to say that a fuse is weak for the needed purpose, but not in the sense of a fault which needs to be fixed? – marsh-wiggle May 30 '22 at 11:03
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    @marsh-wiggle I suppose that we should talk about the circuit instead of the fuse. e.g. the circuit can deliver enough power – user253751 May 30 '22 at 11:32
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    @marsh-wiggle the fuse is intended to be the weak link in a circuit because then it fails in a controlled way - analogous to the crumple zone in a car. If the fuse is too small for your needs, that means everything the fuse protects is also too small. So the correct terminology would be “the circuit is capable of handling the required current” not “the fuse is strong enough”. – Tim May 30 '22 at 11:37
  • one of the compressors will run most of the time - Ryan's answer suggests that small compressors are often not rated for 100% duty cycle, so the one taking most of the load could overheat. Unless it's still just bursts of heavy load with time to cool down between. – Peter Cordes May 30 '22 at 16:13
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    @marsh-wiggle "Weak wires" would be correct. The fuse is an afterthought, a mere necessity to protect the wires. What would also be correct is "not enough wires" because giving each of the loads its own circuit is a good way to solve it. – Harper - Reinstate Monica May 30 '22 at 22:14
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    @PeterCordes whether it runs continuously will depend on usage and leakage. If one wants to correct the "problem" then one will need to have a larger, common pressure operated switch that will turn on both compressors simultaneously. The way dual-engine locomotives do it (or dual-compressor streetcars). – Harper - Reinstate Monica May 30 '22 at 22:16
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I would use both compressors to feed a reservoir with oneway valves on each supply.

That way any small pressure difference will not reverse feed a compressor.

Solar Mike
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  • Think the pressure switches would have to be after the one way valves to work. – crip659 May 29 '22 at 12:27
  • Do I understand correctly that you don't see any problem connecting the two compressors if I mount oneway valves in front of the Y connector? – marsh-wiggle May 29 '22 at 12:36
  • @crip659 why do you think the pressure after the valves will be different? If the reservoir is low then the valves open… so the compressor will start due to low presdure. – Solar Mike May 29 '22 at 13:46
  • @marsh-wiggle by "in-front" do you mean upstream or downstream? – Solar Mike May 29 '22 at 13:47
  • @SolarMike between each compressor and the Y connector, allowing just airflow from compressor to the Y connector and not back into the compressor – marsh-wiggle May 29 '22 at 13:51
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I don't think there's any particular issue with connecting 2 compressors as long as pressure ratings match, at least in terms of safety.

However small compressors are often not rated for anywhere near 100% duty cycle, so depending on what you plan to do with them they might end up running hotter than they were designed for, probably shortening their life, and potentially causing other issues like hot moist air. Short bursts like an impact gun is fine but stuff where you're keeping it on for long periods like plasma cutting, blasting or spraying might be problematic.

Also, if they're going to be in the same room as you are, one compressor going constantly is unpleasant enough, I can imagine 2 making slightly different noises would be much much worse.

Ryan Callaghan
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Whenever 2 compressors are connected in parallel, always use non return valves in discharge line, in your case 2 never will be required, after that you can connect a y or T

Arun sood
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