15 years ago
I'm dealing with a control problem that involves a differential pressure
mounted across the check valve after the discharge of a pump.The pump will
be one of four discharging into a common header. The check valve will have a
motor operator on it to open and close it. Pressure in the header will
normally be in the range of 70 - 100 psig.
Before the pump starts, header pressure will initially be higher than the
pressure, of course; but with the check valve closed, discharge pressure
build and soon exceed header pressure after the pump starts. The D.P. switch
sense the difference in pressure and the switch's contact will close, and
cause the valve to open. Once the valve's motor actuator gets an open
command, its own circuit will cause it to seal-in and drive the valve to the
full-open position, until a limit switch stops the motor.
Ideally, what I'd like to find, though, is a D.P. switch with a contact that
when pressure AFTER the check valve exceeds pressure BEFORE the valve (in
case the pump malfunctions mechanically, and there is backflow.)
Has anyone ever heard of such a D.P. switch? And if so, does anyone have a
manufacuter and model number?
I know I could do this with a D.P. transmitter, DC power supply and a signal
module that changes a contact's state when the transmitter's current reaches
a certain level, but
I'm hoping a simple switch could do it instead.
I hope someone can suggest something. But then maybe I'm hoping for too