A gate valve actuator is a mechanical device designed to remotely open and close a gate valve. These actuators are known as multi-turn actuators, as it generally takes at least a couple of full rotations of the valve's control stem to fully open or close the gate. Gate valve actuators are driven by electric motors rated to cope with the often considerable weight of the gate, plus the thrust forces exerted by the fluid passing through the valve. The actuators are generally used in unmanned or remote installations offering convenient long distance or automated control of single or multiple valve systems. Gate valve actuator systems include varying levels of internal control sophistication, but typically include travel and torque sensors, which stop the motor when the valve is fully cycled or obstructed.
Gate valves are one of the most common fluid control mechanisms in general use and may be found in large numbers in a multitude of different industries. The basic principle of gate valve operation centers around a flat, round disc, or gate, which is raised or lowered through guides or channels to obstruct or open the fluid flow path. This action is achieved by turning a lead screw or stem, which passes through a corresponding nut built into the gate. This causes the gate to advance up and down the lead screw, either opening or closing the valve. The rotation of the lead screw may be manually applied via a circular handle or by a powered gate valve actuator.
Powered gate valve actuators are fairly simple in principle and, at a basic level, consist of an electric motor and a set of position sensors. This type of actuator is commonly known as a multi-turn actuator, as the average gate valve takes at least a couple of full turns to operate and may take several hundred rotations depending on the valve design. The motors used on a gate valve actuator are typical three-phase alternating current (AC) types rated to comfortably handle the weight of the gate and the fluid pressure to which it is exposed. Single phase and direct current (DC) motors, however, are sometimes used in specialist applications.
The basic operation of the gate valve actuator is equally simple, with the motor turning the lead screw to lift or lower the gate. The end of travel, or fully opened or closed positions, is generally indicated by built-in sensors that stop the motor when the end of travel has been reached. The activation of the cycle may come courtesy of a remote or local stop/start station, or be part of an automated system. This makes the gate valve actuator an ideal application for unmanned installations or those where valves are located a long way from staff stations.
Gate valve actuators may include fairly sophisticated local controls featuring programmable operating parameters, but are more often than not fairly simple. All will, however, include at least the aforementioned end of travel sensors and a torque sensor, which will also stop the motor if the valve jams or becomes obstructed. This event will generally prevent the motor from burning out and may even flag operators remotely of a failure.
