AWWA C504-15 pdf download.Rubber-Seated Butterfly Valves
4.2.8.1.7 Mechanism design. Worm gear actuators or traveling-nut actu- ator mechanisms shall be self-locking and designed to transmit twice the actuator rated output torque without damage to the faces of the gear teeth or the contact faces of the screw or nut.
4.2.8.1.8 Traveling nut design. Traveling-nut actuators shall have steel drive screws and internally threaded bronze or ductile-iron nuts that operate in a lubricant.
4.2.8.1.9 Worm gear design. Worm gear actuators shall have bronze or ductile-iron worm gears and hardened-steel worms that operate in a lubricant.
4.2.8.1.10 Actuator bearings. Valve actuators using ductile-iron worm gears, for use on valves intended to be buried, shall be supported in the housing and cover with permanently lubricated or self-lubricated sleeve bearings.
4.2.8.1.11 Actuator mounting. Te actuator housing shall be securely attached to the valve body or extension to prevent movement during operation of the valve. If bolting alone is not sufcient, dowel pins or keys placed symmetrically shall be employed.
4.2.8.1.12 Design safety factor. Actuator housings, internals, supports, and connections to the valve shall be designed with a minimum safety factor of 5, based on the material’s ultimate tensile strength, or 3, based on the material’s yield strength, whichever is lower, for the torque transmitting parts of the connection, except for intentional sections of weakness (i.e., shear keys or pins).
4.2.8.1.13 Verifed safety factor. Actuators shall have a minimum obser- vation verifed safety factor of 2, based on the proof-of-design testing in accordance with Sec. 5.1.4.5.
4.2.8.2 Actuator sizing.
4.2.8.2.1 Severe operating conditions. Te actuator should be sized for the most severe operating conditions as specifed. If the purchaser fails to specify the operating conditions, actuators shall be sized for the operating conditions spec- ifed below.
.2.8.2.3 Minimum required shaft torque (MRST). Te minimum required shaft torque (MRST) shall be provided by the manufacturer. Te torque at both the seated position (seating and unseating) and the midstroke maximum (5º though 90°) total dynamic run (opening or closing) shall be evaluated.
4.2.8.2.4 Actuator sizing torque (AST). Te actuator sizing torque (AST) torque shall be calculated by the actuator manufacturer and based on the minimum required shaft torque (MRST) times the application factors (AF) given in Table 4.AWWA C504-15 pdf download.