"RogerN" wrote in message
m...
"Ignoramus5722" wrote in message
...

snip

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?

A more complicated way... :-)

Have a pressure transducer in each tank and a solenoid valve between
them. Possibly with the flow control/check valve in line with the
solenoid valve.

Transducers ran to a controller and a little software.

For this, assuming the compressor starts at or below 90PSI and Stops
at or greater than 125 PSI.

Valve = Primary_Tank_PSI Secondary_Tank_PSI OR Primary_Tank_PSI
120 // Valve ON when secondary can help or when primary is near
full

Compressor = (Compressor AND Primary_Tank_PSI 125) OR (NOT
Compressor and Primary_Tank_PSI = 90) // Compressor turns ON at 90
PSI and OFF at 125 PSI.

RogerN

=================
Check valve from compressor to primary tank, another from secondary to
primary. Normally-closed solenoid valve from compressor to secondary,
opens when primary 90PSI. Can be switched off. Primary feeds shop air
line.

Compressor fills primary first to 90PSI, then solenoid valve to
secondary opens, check valve into primary closes as compressor outlet
pressure drops. Compressor brings up secondary.

If primary drops 90 then solenoid valve closes, compressor reverts to
filling primary.

Once primary is 90, compressor returns to filling secondary.

Normally secondary supplies airline via check valve into primary, is
refilled through open solenoid valve.

When demand is too high and pressure drops below 90PSI, solenoid valve
closes so compressor discharges into primary, as does secondary
through the tank-tank check valve until the demand drops below
compressor capacity. Then the compressor refills the primary, and then
the secondary.

I think that covers everything.
jsw