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the high pressure cut-out and low pressure cut-in settings found in conventional
pressure switches the E30 included a third set point called the “trip pressure”.
The trip pressure can be set to some value that is less than the pressure switch’s
normal switch on pressure. In the event of the system’s pressure falling below the
trip pressure the run-on timer is invoked. The run-on timer can be set to ignore
the state of the pressure for a period of 1 second to 900 seconds (15 minutes). If
the system pressure recovers and rises above the trip pressure before the end of
the run-on time the E30 immediately reverts to normal operation. If at the end of
the run-on the pressure has not recovered and remains lower than the set trip
pressure then the E30 will shut down the pump.
The advantage of this system over a conventional mechanical loss of prime
pressure switch is that the E30 can tolerate dips in pressure for short periods
without tripping out and stopping the pump. Often momentary dips in pressure
occur when valves open in irrigation systems. The E30 is able to ignore these
pressure uctuations while still providing loss of pressure protection when a
genuine problem occurs.
If you leave the trip pressure set to zero the E30 reverts to operating like a
conventional pressure switch with no loss of pressure protection.
Mode 2 Pressure Guard
If you choose to use the E30 in mode 2 the pressure switch will function as a
pressure guard. The pressure guard allows you to set a starting and stopping
pressure and a trip pressure. In addition, a start-up timer and a run-on timer are
included. The pressure guard functions as a protection device for systems that
are normally controlled by other means. For example, a variable speed drive that
is fully controlled by a 4 to 20mA pressure transmitter may benet from the
inclusion of an E30 operating as a pressure guard. In the event of a problem
developing with the VS drive or with its pressure transmitter, the E30 is able to
override the system and shut the pump down if the pressure rises above or falls
below settable limits. The E30’s run-on timer facilitates momentary dips in
pressure without invoking the pressure guard’s loss of pressure protection and
the E30’s start-up timer allows time for the system to pressurise before the
pressure protection functions commence.
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