Valve to fill additional compressed air tank

I have a strange sounding idea. I want to have an extra compressed air tank in my system. I have a bunch of tanks at this moment to choose
from. This way, I could run air hungry tools like breakers, etc, intermittently but longer.
So far, so good, and nothing complicated. I have a whole bunch of tanks right now, and thought to do something nice for my shop and have an extra tank.
Examples of tanks I have are:
http://igor.chudov.com/misc/ebay/tmp/Marengo/186.jpg
http://goo.gl/PdkzbM (Tank with "QT-15" lettering on left)
However, I also realize that with a big extra tank, it will take so much longer for the air system to come up to pressure. This will be my wasted money, as people will be waiting longer to use compressed air.
So, I thought, can I have a valve, that would not fill the tank, until system pressure reached 120 PSI. And then it would shut off again if the pressure ever falls to below 90 PSI.
To use the accumulator tank to supply air, another pipe would be used with a check valve.
This setup makes sense to me, as
1) I would get the system to reach pressure quickly and 2) I would eventually get a supply of air in the accumulator, without ever dropping the system pressure below 90 PSI.
I do realize that I can accomplish what I want, with a electric pressure switch and a normally open pneumatic valve. But I thought, perhaps, there is a purely pneumatic valve that does this? What would it be called?
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Ignoramus5722 wrote:

Add compressor capacity, rather than tank volume, presuming you have a reasonable size tank now. Set the pressure switch for the second compressor to come on as say 10 psi below the first's cut in pressure so it will only come on when the first is unable to keep up with the demand.
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Yep, Ig. Remember, no matter HOW large your tank, you can never use more air per minute - on average - than your pump will supply.
LLoyd
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On 2013-12-07, Lloyd E. Sponenburgh <lloydspinsidemindspring.com> wrote:

Lloyd, and Pete, I appreciate your opinion and I do understand that I cannot get more compressed air per hour with an extra tank.
But, I want an answer to my originalquestion,as I do see a big benefit in what I want to accomplish.
i
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Ok... just put a uni-directional flow-control valve (with a ball check in it) between the 'main system' and the reserve tank. Control the flow (slow bleed) INTO the reserve tank, but let it back-flow freely into the main system any time its pressure is greater than the system.
Then the main system will pump up _almost_ as fast as it would without the reserve, slowly bleeding air into the reserve as it goes. When sudden demands occur, the reserve will freely feed the whole system.
Such valves are purely mechanical, one-piece assemblies... ball-check and flow control (often needle type) valve in one unit.
Lloyd
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"Lloyd E. Sponenburgh" <lloydspinsidemindspring.com> fired this volley in

Here's one that'll do 83scfm in the free-flow direction, and the schematic symbol.
http://www.mcmaster.com/#45045k44/=pp43sh
LLoyd
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"Lloyd E. Sponenburgh" <lloydspinsidemindspring.com> fired this volley in

Oh... that one is a poppet style, not ball-check, but I've used that model, and they last for years and years.
Lloyd
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On 2013-12-07, Lloyd E. Sponenburgh <lloydspinsidemindspring.com> wrote:

Lloyd, I thought a lot about this, and I think that it is the best solution because it is so simple, and also is friendly to the air dryer that would be between the compressor and the additional tank.
Thank you. I Saved your suggestion. I will talk to my shop guy and if I put in the second tank, I will use this valve.
i
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Pete, I would like to explore my idea in the original post, for now. I do not really want to get more compressors, for now. Even though it is tempting to upgrade,I just bought a 15HP Quincy 370 compressor. My shop guy wants me to upgrade my 10HP quincy to this one.But I do not want the hassle of upgrading the wiring and dealing with a messy wiring duct.
i
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40 feet, I believe 10 gauge, 30 amp breaker, 220v
i
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I have about 1200 lbs of cables. But my problem is that the wire going to the compressor, goes through a 48 year old wire duct. I am afraid of messing with it. I do not even know how I am going to figure it out.
Perhaps I should start with a clean slate, and get a new 50A circuit to the compressor, with a real neutral, etc, through a separate conduit. And then upgrade the compressor from my 10HP QUincy to the 15HP quincy that I bought on auction. My original plan was to sell the 15 HP compressor. But maybe I should keep it and sell the 10HP inspead.
i
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Amen!
Lloyd
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Ig, you're mistaken about people "waiting for air". Unless their net usage is higher than the pump capacity, the pump will come on when the combined tanks get to the desired cut-in pressure, and shut off when they get topped off, just like they do with smaller tanks. The difference is, that they can use air-hogs longer before they have to stop.
The total duty cycle will remain approximately what it was before. The pump will stay on longer, yes; It'll also stay off longer.
You don't need _any_ valves to accomplish what you want. You're over- thinking it.
(although you should provide manual valves to isolate tanks, in case of a leak or a service issue)
Lloyd
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On 2013-12-07, Lloyd E. Sponenburgh <lloydspinsidemindspring.com> wrote:

We do not have the compressor on at all times. We turn it on in the morning or when it is necessary.

Exactly.
But when we turn the compressor on in the morning, when we need air, I do not want to wait extra 15 minutes.

No,I do need that for start-ups.
i
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On Fri, 06 Dec 2013 20:03:43 -0600, Ignoramus5722

So isolate a smaller tank before the large and use a ball valve to shut down the main tank and use the smaller one for quick air needs. It could easily be valved both to the compressor and to system air, with a single line for your immediate use. Keep the little guy filled and only open him when you need a dustoff.
--
Make awkward sexual advances, not war.

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Sounds like you have a bad leak if the system won't hold air overnight.

Filling the extra tank through a throttle valve and delivering the stored air through a check valve will do what you want, but the energy efficiency will be around 50%. It's the same story as charging a battery through a resistor. A manually-operated valve would be better if its operation can be timed to miss the demand peaks.
If your peak loads are sufficiently infrequent (once in ten compressor cycles or some such) the resistive reservoir charging might be useful. For my part I'd try to make the system hold pressure when the shop's closed. Compresed air is basically money.
Hope this helps,
bob prohaska
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Exactly. Like charging battery through a resistor.
A pressure controlled solenoid valve would be better.

I think that I should try to get my act together and find leaks. Plus the dryer dumps a bunch of air every 2 minutes, very annoying.
i
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... But I thought,

It's a pressure relief valve. With an exit port, not just venting to air. The tricky part is finding one with an adjustable differential, so that it could be made to stay open until 90 psi. Bob
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That doesn't solve the filling part, only the 'feeding' part.
A one-direction flow control valve will do both.
Lloyd
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On 12/6/2013 9:28 PM, Lloyd E. Sponenburgh wrote:

Yeah, it does: the relief valve "in" is connected to the basic tank and the "out" to the auxiliary tank. When the basic tank reaches 125, the relief valve opens & delivers air to the aux tank.
Unless I'm missing something, which wouldn't be the first time.
Bob
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