Valve Magazine - Winter 2012

Rack & Pinion Actuator Electric Actuator

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ACTUATORS & CONTROLS

Pneumatic Actuators

TRIAC Rack and Pinion

• 100– 36,000 in lbs torque

THD Heavy Duty Scotch Yoke

• 7,000– 1,600,000 in lbs torque

Stainless Steel Rack and Pinion Actuators

180º Pneumatic Actuators

Electric Actuators

WE/XE Series

• 500-25,000 in lbs torque
• Single Phase and 3-Phase
• Integral Controls
• On/Off and Modulating
• Optional Battery Failsafe and
Spring Return
• Weatherproof NEMA 7 and
ATEX Explosion-Proof
• AWWA, CSA

Control Accessories and Custom Mounting Hardware

are routinely produced with reduced port sizes to keep the operating torques low. For example, a power plant ball valve with a nominal pipe size of 1. 5 inches may have an actual through-port opening size of only 5/8 inch. CONTINUED FROM PAGE 29

SELECTION

The port size should be considered when specifying power plant ball valves. A reduction in port size causes an increase in system pressure loss through the valve, which results in an increase in fluid velocity through the restricted port. Power plant ball valves were originally and primarily designed for vent and drain applications. Since vents and drains normally are used for short durations, the increase in velocity through the ball port does not produce a large wear factor. However, in continuous process applications, the system pressure loss and the velocity also will be continuous, which can mean premature failure of restricted port valves.

High energy piping systems in power plants use schedule 80, 160, and XX-Heavy pipe. Table 1 shows the correlation between pipe size and pipe internal bore for several nominal pipe diameters and schedules.

Power plant ball valve manufacturers use the relationship between nominal pipe size and pipe internal diameter to determine “standard” port sizes. Several companies publish dual Cv values—one for the valve and one for the valve installed in heavy wall piping. The port size, the system operating characteristics and the piping configuration during the valve selection process should receive close attention. For example, if the ball valve is to be used for isolation either before or after a control valve, the question becomes: How will a smaller or larger port affect the control valve performance?

Many power plant ball valve manufacturers offer increased port sizes as an option. Largely, this option is a result of the “TDP-1-1998 Recommended Practices for the Prevention of Water Damage to Steam Turbines Used for Electric Power Generation,” which offers guidelines for the relationship of the valve