Can electric control valve actuators provide the power (torque or thrust times speed) of a pneumatic unit?
WARNETT: Pneumatic control valve actuators are capable of significant thrust and speed. Thrust is a function of the surface area of the diaphragm or piston employed. Provided there is sufficient flow into the actuator, then relatively fast speeds can be achieved. More important for a control valve, however, is the speed of response to a change in set point. A pneumatic actuator often suffers from dead time. This is the time it takes to build up sufficient air pressure to overcome static friction in a valve. Dead time becomes more significant as the changes in set point become smaller. The normal movement during the life of a control valve consists of millions of small changes in position. Because the new designs of electric control valve actuators have no dead time, the response to a change in set point is almost instantaneous. That leads to closer control of the process variable (e.g., temperature, pressure or flow), and, therefore, more efficient utilization of the plant. VM: There a