Page 47 - Apollo - Actuation

P. 47

APOLLO® BALL VALVES

BALL & SEAT
Valve torque is primarily dependent on the friction between the moving ball and the stationary seat. Seating material and
surface finish of the ball establish the basic frictional characteristics of the combination. Service conditions also play a major roll
in modifying the effects of friction. A floating ball valve utilizes the difference between the upstream and downstream pressures
to force the ball into the downstream seat. When this force exceeds the forces in the original assembly, the torque required to
rotate the ball increases. Process media may also increase or decrease the friction between the ball and seat. To insure reliable
actuator selection, the service conditions of the installed valve must be carefully determined and considered for their effect
on torque.

STEM & PACKING
Stem torque is primarily dependent on the frictional characteristics of the packing material and the tightness of the packing
adjustment. Proper adjustment of the packing is important not only to the leak tight performance of the valve but also minimizes
the operating torque. Tightening the packing more than is required to establish a proper seal, only increases torque requirements
and stem wear. Packing adjustment can be abused to the point that a properly selected actuator may not be able to operate the
valve. Stem packing friction is essentially unaffected by the media and operating pressures within the valve.

-24/-29 GRAPHITE STEM PACKING ADDER
The selection of graphite packing contributes significantly to the operating torque of a valve. The friction factor for graphite is
a magnitude different than that of PTFE based packings. The contribution to torque is a function of the stem diameter and is
reflected in each of the following tables. When selecting either the -24, -29 or -65 options use the appropriate adder listed in the
table for each valve as a direct increase to the base torque constant.

BREAKWAY TORQUE
Torque required to initiate the opening of a valve from the fully closed position. This is the highest torque requirement anywhere
within the Apollo® Ball Valve’s rotation. The Torque Constants Chart lists breakaway torques for Apollo® valves under defined
operation conditions.
Note: For double acting actuators, the torque output at the given air supply pressure must exceed the breakaway torque of the valve.

CLOSING TORQUE
Torque required to rotate the valve from the open position, into the fully closed position. A conservative approach is taken when
determining closing torque because operating conditions have a significant effect on its value. It is safest to assume that closing
torque is equal to breakaway torque. In actual service conditions the closing torque may be less, but this margin is used as a
sizing safety factor.

GUIDELINES FOR DETERMINING IN-SERVICE VALVE TORQUE
Actual service conditions must be considered when determining a valve’s required torque. Torque Adjustment Factors have been
established to convert the Torque Constant value to an in-service torque. Multiple Torque Adjustment Factors may be required
to establish the proper in-service torque requirement. All valve torque determinations begin with the Torque Constant value at
the appropriate differential pressure. Adjustment factors must be used to determine the in-service valve torque requirement
(see page 52, Torque Adjustment Factors Chart). Each applicable adjustment factor is applied to the value from the Torque
Constants chart. The sum of all appropriate adjustments of the valve’s torque are added to the original value from the Torque
Constants chart. The result is the in-service torque requirement. This torque value is to be used in actuator selection.

Note: For fail closed applications, the closing torque must be exceeded by the “spring end” force of the actuator. For fail open
applications, the closing torque must be exceeded by the “air end” (at the given supply pressure) force of the actuator.

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