Digital Magazine

Valve Actuators with Longer Lifespan

QTRCO has innovated actuator designs specifically for high cycle, high speed, high reliability applications

For paper, film and foil converters, QTRCO has created innovative actuators that eliminate the design limitations of the actuator “lunchbox.”

The actuator, which gets its name from its one-piece aluminum extruded body and cylinder that resembles a lunchbox, is popular because it is compact and inexpensive. However, aluminum lunchbox actuators are not very reliable and often break in more demanding environments or applications.

To resolve many of these issues, QTRCO designed an actuator with an internal “rack and gear” mechanism as an alternative to its traditional rack and pinion design.

The actuators are designed with offset cylinders that align the piston axis with the pinion gear pitch circle diameter, eliminating cantilever forces and friction. The company also replaced the sliding blocks, wear pads, and bushings with specialized rollers. As a result, the rack and gear actuators have extremely low internal friction.

The new design also eliminates one of the primary causes of failure of a lunchbox actuator: the O-rings on the shaft. In a lunchbox actuator, air is forced through ports in the body. The air pushes the piston outwards, and springs push the piston back in. Each cycle pressurizes the shaft, which typically has two O-rings, one at the top and one at the bottom. As the shaft cycles back and forth 90 degrees, the reciprocating motion places significant stress on the O-rings.

In QTRCO’s design, this action is reversed, and the air is forced inward through the end cap. The spring return applies no pressure to the shaft seals, which prevents premature O-ring wear.

This configuration also has benefits when valve throttling is required. Due to the design of the company's Q Series and because the piston is located close to the end cap, much less air fill volume is required, and the actuator responds much quicker and is easier when throttling.

QTRCO took a similar approach as an alternative to Scotch yoke actuators. Also known as a slotted link mechanism, the Scotch Yoke is a simple and effective mechanism that has been used for a long time. However, with typical Scotch Yoke actuators, the force applied to the piston rod is also applied to the shaft and shaft bushings, resulting in friction and bushing wear.

To resolve these issues, QTRCO designed a patented Flat Yoke mechanism that can accurately and reliably position any rotary control valve requiring up to 500,000-inch lbs. of torque.

The Flat Yoke is designed with quad body slots that absorb the mechanism’s side loading forces, leaving the piston rod completely free of bending stresses while allowing termination of the rod at the yoke. Like the Q Series, these F Series actuators also have extremely low internal friction, consume minimal air volume, and can handle the most severe throttling applications.

For more information, visit https://qtrco.com/ .

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