This model comprises of hydraulically actuated diaphragm liquid heads incorporating a diaphragm actuated replenishing system along with an actuator and controller. The working principle of this pump is identical to that of the Simplex Hydraulic Diaphragm series.

The only difference is that an electrical actuator is mounted on the top of the pump. With the help of this actuator and the stroke controller, the stroke length of the pump can be controlled automatically with the help of an input signal of 4 to 20 mA.

An electrical actuator is a device which converts electrical energy derived from a motor to corresponding mechanical movement, which is imparted on the final control element. Each electrical actuator is provided with a hand wheel with clutch for manual operation in case of power failure. A continuous local mechanical position indicator is provided which shows real-time opening/closing of the actuator irrespective of whether the actuator is in manual or electrical mode.

These actuators work with an input signal of 4 to 20 mA. Normally, a 4 mA output signal corresponds to fully closed (i.e., 0% stroke length of the pump), and 20 mA corresponds to the fully open condition (i.e., 100% stroke length of the pump). A feedback potentiometer fitted inside the actuator converts the mechanical movement of the actuator to a corresponding resistive output. A two-wire position transmitter (PPT) converts the resistive output of the actuator-mounted feedback potentiometer to a corresponding 4 to 20 mA current output.

A positioner unit, which also acts as a comparator, compares the input signal of 4 to 20 mA (based on process parameters) with the feedback signal of 4 to 20 mA generated from the actuator-mounted PPT and generates open/close relay signals through ICs, which are routed through an RC network for forward and reverse movement of the motor until the desired position is achieved.

The actuator, which is mounted on the pump, with its change in linear motion due to the input signal given, in turn changes the stroke length of the pump, resulting in the desired flow.