Metachem Corporation also manufactures high precision, positive displacement, reciprocating plunger pumps with automatic stroke controllers. The mechanical operation of these pumps is identical to plunger pumps, but the only difference is that the stroke adjustment of the pump can be operated manually as well as in auto mode with the help of an electrical actuator which is mounted on the top of the pump.

The electrical actuator is connected to the stroke controller which shows the percentage stroke length of the pump. The actuator works with an input signal of 4-20 (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 and 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 4–20 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 4–20 mA current output.

A positioner unit, which also acts as a comparator, compares the input signal of 4–20 mA (based on process parameters) with the feedback signal of 4–20 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.

The rest of the pump mechanism is identical to that of our Simplex Plunger series.