Do you know the electric stroke adjustment of reciprocating compressor?
The actuation of the stroke length adjustment can also be carried out by an electric actuator. This may be done by using the local controls right on the actuator, but in most cases, is carried out remotely from the control room. This has the significant advantage of being able to automate processes.
To this end, the control room sends a signal to the electric stroke adjustment unit, which adjusts the stroke and also outputs feedback to the control room, creating a closed control loop. One example of a electric stroke adjustment can be seen in figure 1.
Figure 1: Example of an electric stroke adjustment
Rotary actuators for electric stroke adjustment can be attuned precisely to each drive unit in collaboration with the manufacturer. These rotary actuators mainly consist of an electric motor, a worm gear, an integrated non-intrusive control unit and a handwheel for emergency operation. The actuators are designed for control operation in the rated operation class S4-25%, i.e. for periodic intermittent duty with effect of the start-up process and a duty cycle (DC) of 25%. The motors are protected from overloading by a PTC (Positive Temperature Coefficient) thermistor.
As when selecting the pump drives, both the ambient conditions and customer requirements must be taken into account when selecting the actuator. This primarily includes information about the voltage and frequency, the number of phases (DC or AC current), the desired actuation type, the ambient temperature and information about required explosion protection.
If the pump is operated in the Ex area, explosion-proof actuators must be used that are designed so that they cannot generate ignition sparks or hot surfaces, and thus cannotbe an ignition source. Figure 2 shows such an ex-proof electric actuator. All actuators are also dust-proof and protected against both spray water and long-term submersion in water. Use in particularly cold environments (< -20°C) is also possible; however, the installation of a heating unit must be taken into account. In order to ensure that positioning accuracy is as exact as possible, and to protect the actuator from overloading, the actuators are equipped with both position and torque measurement.
Figure 2: Sectional view of an electric actuator (AUMA 2017)
Actuation takes place via the integrated control unit. An analog 4 to 20 mA signal is used for this purpose as standard. However, HART Protocol, Foundation Fieldbus, Profibus DP or Modbus RTU can also be used, depending on the design of the pump. In addition, the customer has the option to dispense with the integrated control unit and operate the actuator using a potentiometer with its own external control system.