In our recent newsletter entitled
Automating a Valve - Why?, the beneficial reasons to automate a valve were covered, as well as what automated valves are able to do. In this letter, let's look at the differences between pneumatic and electric valves, and the purpose of each.
Typically, actuators are designed to perform one of the following operations:
Moving the valve from open to closed, closed to open, or somewhere in between
Keeping the valve in a specific position, depending on process-control requirements
Seating the valve properly, to isolate the media
Providing a safety mode in the event of a system failure
Providing proper valve operations to control required processes.
When choosing between pneumatic or electric actuation, there are certain application conditions that will determine the best actuation system for the job. Important factors include the available power source, speed and frequency of operation, the size of the valve, and environmental conditions.
Normally, it is the job of the process engineer to choose between pneumatic or electric actuators for the application. There are specific advantages to each type, and it is good to consider each to make the proper selection. The table below summarizes some of the different features and capabilities of each type of actuated valve.
PNEUMATIC
ELECTRIC
Variable speed - uses exhaust air with a needle valve
Fixed speed - pulsing circuit may be added to slow speed
Simple, accurate, and inexpensive
Additional expense, when compared with pneumatic
Requires 40-120 psi clean air supply
Operates using standard 110 vac power supply
Temperature range: -4 to 176° F
Temperature range: -40 to 140° F
Safe to use in most hazardous areas - explosion, shock, and spark proof
Requires NEMA 7-rated housing to operate in hazardous areas
Fail-safe models are practical and economical
Fail safe models include spring packs or battery back-up
Operates effortlessly in high and fast cycle times (100% duty cycle)
25% duty cycle is standard - options are available for upgrade
Won't overheat
Can overheat
Can be used in wet environments
Must be sealed from moisture
Optional valve positioner required for throttling applications but results aren't as accurate
Positioning control board required for throttling with high accuracy
Look for more information on the best application and sizing procedures for pneumatic and electric actuators, along with available options and accessories. If you have further questions about actuated valves, or any valve or application, please visit
www.milwaukeevalve.com, or contact your
Milwaukee Valve sales representative.
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"Milwaukee Valve is honest and dependable, so I have confidence when making the specs on projects. They help us save time, money, and effort."
Joe Tagliaferro - BR+A Consulting Eng.
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