Electric and pneumatic motor operated actuators often operate very large valves. They also actuate high-pressure globe valves, which require very high thrust loads to shut in compressors. Normally, electric motors also operate gate valves because of their high thrust loads.
Their disadvantages are that they cannot be made fail-safe, that they have more moving parts, and that they require more maintenance. When used as EBVs, the electric motor’s power supply should be redundant or be backed up by an emergency power generator. In a fire zone, the motor, actuator and control housing, and the conduit must be fireproofed. Refer to Section 1368. Both electric-and pneumatic-motor actuators work with an adjustable torque switch to control the seating of the valve.
To avoid corrosion problems, air or gas supply for pneumatic motors must be clean and dry. As EBVs, pneumatic motors must have a very secure source of gas, such as instrument air backed up by nitrogen.
Pneumatic and electric motor actuators can operate gate, globe, ball, Orbit, and butterfly valves, ranging from NPS 1 to 36 and ANSI Class 150 to 2500. See Figure 1300-13 for typical electrical motor installation.
The most common brands of electric motor-driven actuators are:
Limitorque also makes pneumatic, motor-driven actuators.