Manual Actuators.pdf - Val-Matic Valve and Manufacturing Corp.

ACTUATOR OPERATING CHARACTERISTICSThe last important consideration in selecting an actuator is the different operatingcharacteristic of the two types. The worm gear has a linear characteristic whichmeans that for every turn of the handwheel, the valve is rotated the same amount.The traveling nut actuator, on the other hand, exhibits “characterized closure.”Characterized closure means that during the first half of closure, the valve is rotatedrapidly, and during the last half of travel, the valve is rotated slowly toward the closedposition. This difference in travel is a result of the geometry of the link and levermechanism. The benefit of characterized closure is that the valve is closed during itslast portion of travel slowly, which can reduce pipeline surges or water hammer.Traveling Nut vs. Worm Gear100%90%80%70%Valve Position (% Open)60%50%40%30%Worm Gear20%Traveling Nut (LS)10%0%0% 10% 20% 30% 40% 50% 60% 70% 80% 90% 100%Actuator Stroke3