Connecting two portable air compressors to a common air receiver


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Old 08-01-11, 07:23 AM
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Connecting two portable air compressors to a common air receiver

We have two portable (diesel engine driven) air compressors of 375 CFM 8 bar rating.
We want to connect these two compressors to a common air receiver. Is it possible to control duty/standby and alternate starting like in the case of electric motor driven compressors?
 
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Old 08-01-11, 09:50 AM
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Possible? Certainly, but not really a question for a site that is really for homeowner DIY questions.

How you would do the control interconnect depends upon the individual controls on the two machines and the sophistication of the desired control scheme.
 
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Old 08-01-11, 05:30 PM
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I agree with Furd, the receiver (tank) would have to govern all the start, stop, standby protocols. This may require a separate, electrically engaged set of controllers, with defaults set up as to which one is master and which one is slave, if you only wanted one to run at certain times. Wow, 750 cfm, that powers some big equipment! But I guess you have them in Saudi Arabia, huh?
 
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Old 08-01-11, 06:14 PM
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I consider a 750 CFM machine rather small. While i did have a couple of 250 CFM compressors these were only used for load peaks with the bulk of the machines being 2,000 CFM or larger. Something like 21,000 CFM ultimate capacity.
 
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Old 08-02-11, 02:43 AM
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Sorry about posting my query here, but going thru other threads it seemed to me that there are experienced members over here who could help! We use compressed air mostly for sand-blasting precast concrete elements, which consumes lot of air, for operating air tools like pneumatic poker vibrators, various air tools and cleaning.
In the individual machine there is pressure switch, unloading valve which load/unload the compressor, the engine continues to run on idle when the compressor is unloaded.
If we connect these two m/cs to a single receiver, is it possible to control such that say comp 1 loads and fills the tank, unloads, next time there is demand, comp2 loads and so on. When there is a greater demand, both run at the same time.
It is possible if they are electric-motor driven compressors, but can it be done with engine -driven ones?
 
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Old 08-02-11, 06:35 AM
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You'll need a couple of adjustable pressure pilot valves like the one here:

GAS AIR COMPRESSOR PILOT CHECK VALVE COMBO 140-175 PSI | eBay

If you adjust one to cut in about 10 psi below the other one, you can control demand. Hook them up to the existing individual throttle controls and the second unit will kick on if the pressure in the tank gets low. That'll solve your cfm load control problem, but will not give you alternate starts (unless you want to readjust the pilots all the time). I don't know how to do it with pneumatics, most likely you'll need to program a separate pcb for that and work it out with electrics. Why don't you check with the manufacturer of those units, there may be a simple solution for this already. Good luck.
 
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Old 08-02-11, 11:37 AM
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If manual starting of the compressors and having them run unloaded at idle is acceptable then alternating the load/unload cycles between the two machines is fairly easy.

I would caution against alternating each machine on each cycle because it will cause each machine to have equal hours load time and that means each machine will require routine maintenance at the same time and that they will both wear out at about the same time. That used to be standard operating procedure but it makes more sense to do both maintenance and repair / replacement on a schedule that allows sufficient time to do the work correctly rather than hurry it up because BOTH machines are due.

The scheme proposed by Markiz37 is a good one and by use of a simple four-way valve in the pneumatic control tubing between the two machines and the two pilot unloaders you can easily switch the lead / lag machines with a turn of the valve. If you have standard electric available it can be done with solenoid valves and an alternator relay.

Tell us more about the manufacturer of the compressors and their individual control schemes. How much money you have to spend on this project, the required time frame and do you prefer a semi-automatic pneumatic control or a fully automatic electronic control.
 
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Old 08-03-11, 02:29 AM
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I get the idea - 4-way valve and 2 unloaders. Think sem-auto pneumatic control will suffice. Thanks a lot Furd, Markiz37 and Chandler
 
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Old 08-03-11, 09:40 AM
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Here is what I would do for a test. Connect both machines to a common receiver. Set the governor (unloader) on one machine ten psi lower (or higher) on one machine. Start both machines and see how it works. Of course in this test the machine with the higher governor pressure will be the "lead" machine and the second machine will only come on if the first cannot supply the entire load.

If this works satisfactorily then you can go the route of two new governors (pilot unloaders), the four-way valve and associated tubing. I strongly suggest using the same model of governor as already installed on the machines and also retain the original governors on each machine as back-up controllers. The machine-mounted governors will need to be set at a pressure slightly higher than the auxiliary receiver-mounted governors which will be connected between the machine-mounted governors and their associated unloader valve.
 
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Old 08-03-11, 03:17 PM
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Furd's suggestion would save a lot of speculation about what you should do.
I have many times just connected two compressors with receivers to a common air supply line.
An extra receiver should not even be necessary unless you experience unwanted short cycling.
 
 

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