Coupling 2 different PSI rated tanks together

by George
(Washington, DC, USA)

I have a system with a 240 gal / 250 psi rated tank and a 240 gal / 400 psi rated tank. They are currently coupled together, and the system operates at 200 psi. However, the field personnel want to increase the system pressure to about 380 psi. Is there a way of having both tanks in the system without the 250 psi tank being overpressured? I am trying to use what is already there. Or is that impossible and I must get a 400 psi tank? Thanks.


The system serves two air start systems (one engine at 150 psi and the other engine at 200 psi) with one engine requiring ~350 cfm at 200 psi to start (calculated from the engine bore and stroke). The field personnel, which uses the engines for training purposes, want the tanks to recharge in 10 minutes and foresee several engine starts over a 50-minute period with simulated fail starts (a limiter switch limits a failed start cranking time to 10 seconds).

Not sure if simply increasing the pressure to 380 psi in the system would help with less charging time or multiple engine starts. I am also considering adding another compressor (Gardner Denver model APKAAD with Bore & Stroke 4-3/4 & 2-1/2 x 4) in parallel to the existing same compressor. The

The overall goal is to improve the charging time of the air tanks and to provide multiple engine starts over the 50-minute period.

Comments for Coupling 2 different PSI rated tanks together

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Feb 03, 2016
Tanks...What is your goal?
by: Doug in s.d.ca

OK, much better understanding now.

Using the surplus tank is good.

Have fun.

Feb 03, 2016
Re: Coupling 2 different PSI rated tanks
by: George

Yes, starting the 735 hp, 8 cyl diesel engine several times over a training class period (typ. 50 minutes) would be the fundamental goal and is drawing down the air.

The sequence of operation is essentially the same as I arrived at yesterday. I checked the helpful responses today.

I am replacing the 250 psi tank with a surplus 375 psi tank from another location in the facility, and the 375 tank was used on the same trainer EG. Makes things a little easier, but might still keep the solenoids to isolate the 375 (lower pressure tank) as Bill explained.

Now if I had dedicated systems for each EG (375 psi system for the smaller EG and 400 psi system for the larger EG), then perhaps I could run a hose from the 375 tank to the 400 psi tank outlet in case one of the compressors has an anomaly.

Thanks again for the helpful responses so far.

Feb 01, 2016
Tanks...What is your goal?
by: Doug in s.d.ca

"The overall goal is to improve the charging time of the air tanks and to provide multiple engine starts over the 50-minute period."

By "improve the charging time", you mean shorten?

The terminology is a little confusing...the engine(s) starting more often is also a goal?

What is drawing down the air from the tanks?

What Bill said would be the way to connect both tanks, but I'm not sure that's what you want, especially given the field people's desire to increase the pressure to 380 or so psi.

Feb 01, 2016
Combing two different rated compressor tanks
by: Bill

Sure, I wouldn't have a problem setting up a circuit for that.

It would involve pressure sensors, some solenoid valves, check valves and so on.

Essentially, you would fill both tanks to the rating of the lowest PSI tank, and when the pressure reached that lower PSI level, isolate that lower PSI from the continuing buildup of pressure in the second tank.

On the outflow, air would be drawn from the higher pressure tank first and once that tank pressure reached the lower tank pressure, air could feed the mains from both.

Care must be taken to ensure that the PRV in the lower pressure tank will release air long before the tank pressure reaches critical levels, and probably for redundancy, I'd want to go with 2 PRV's in the lower pressure circuit to ensure that the lower PSI rated tank wouldn't over pressurize.

Of course, your compressor has the capacity to fill both tanks?

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