Thrust forces are equal and
opposite resulting in zero
Traditional Scotch Yoke Actuators
For larger ¼ turn valves, the scotch yoke mechanism provides an ideal
torque characteristic due to the longer effective lever arm and angular
contact at the ends of travel.
But a very high bending force
acts on the rod, necessitating a
supported through rod.
And while available from many
sources, nearly all scotch yoke
actuators for larger valves
are based on a single lever, a
through rod with springs, and
pistons located at opposite
ends of the assembly. Designs
differ primarily in how the rod
is supported—from simple
rod bushings to more effective separate components.
TRADITIONAL SCOTCH YOKE ACTUA TOR DEFICIENCIES:
• Force imbalance –
100% of the operating
forces also act on the
shaft bushings, creating wear and torque
• Proprietary, over-priced, rod seals (and in some designs, similar
seals used internal to the pistons) that require removing the
actuator from the valve and costly skilled labor to replace.
• Changing action from fail clockwise to CCW requires a complicated, labor intensive interchange of the piston and spring ends.
The Ingenious QTRCO Flat Yoke™
At QTRCO, we began with a scotch yoke mechanism but rather than modify existing
designs, we threw them out and started with a blank sheet. We rationalized:
• If we used a two arm lever, shaft bushing loads, wear, friction and torque loss would
• Since we could not have a two arm lever and a through rod, we created an innovative slotted body design that absorbs all side loading and allows termination of the
rod at the lever slot.
• RESULT We can locate identical force modules on each end of the body module
• Balanced weight
• Balanced forces
• Less wear
• Lower friction
• Smaller, lighter springs
• Smaller pistons
• Zero side loading of the piston rod
• We also rationalized that if a seal does not exist, it cannot fail. We placed the springs
inward of the pistons and eliminated all dynamic seals except the piston o-rings.
• And, since the piston o-rings can be accessed while the actuator remains on the
valve, the need to remove the actuator from the valve is eliminated. This prevents
possible valve stem damage and eliminates the high cost of heavy lifting equipment, hours of labor, extensive downtime and lost process.
• ADDED BONUS If contaminants have scratched the cylinder bore, the cylinder can
be turned end to end and re-installed with the unused inward end now serving as a
• Since both the top and bottom sides are identical, action reversal is achieved by
simply turning the actuator top side down.
• And finally, our Flat Yoke™ actuators are manufactured in the USA from USA parts
for optimum quality, with an unparalleled three-year performance guarantee (see
our website for details).
888.ACTU8. IT | www.qtrco.com
Actuators that deliver UPtime.
Proud Member of the Valve Manufacturers
Association of America