This automation industry quiz question comes from the ISA Certified Control Systems Technician (CCST) program. Certified Control System Technicians calibrate, document, troubleshoot, and repair/replace instrumentation for systems that measure and control level, temperature, pressure, flow, and other process variables. Click this link for more information about the CCST program.
Which of the following valve actuation methods would be the best choice for an application that requires a very large force and a small actuator?
a) pneumatic actuation
b) hydraulic actuation
c) manual actuation
d) electrical actuation
e) none of the above
Click Here to Reveal the Answer
Although many pneumatic actuators can provide a large force, they require either a large diaphragm area (in the case of a diaphragm actuator) or a large cylinder (in the case of a rack and pinion actuator).
Manual actuation is accomplished by turning a valve handle, and is limited to the amount of force that an operator can exert on the lever or hand wheel.
Electric actuation delivers high torques for rotary-style valves, but electric actuators tend to be large and heavy compared to hydraulic actuators.
Hydraulic actuators are driven by a high-pressure fluid (up to 4,000 psig) that can be delivered to the actuator by a pump that is remote from the actuator itself. Hydraulic cylinders can deliver up to 25 times more force than a pneumatic cylinder of the same size.
The correct answer is B, hydraulic actuation.
Reference: Goettsche, L.D. (Editor), Maintenance of Instruments and Systems, 2nd Edition