The most common use for parallel disc valves such as stainless steel Y strainer today influences pipeline industry, where elastomer seat seals and ambient operating temperatures make valve virtually leak proof. Parallel gates may also be used in some ruthless, temperature steam applications, in lowering the possibility of locking the disc from the closed position because of a radical alteration of temperature.
Regardless of disc design or type, the gate valve closure element must also come in perfect hitting the ground with seats from the valve body. The body seats could possibly be welded, screwed, pressed or swaged in, or even be integral with all the valve body. Most industrial steel gate valves utilize seat rings which are welded in the valve body. For most with the 20th century typical was screwed in seat rings in steel valves. However, advances in welding and valve repair techniques made the screwed-in rings obsolete. Seat rings and valve discs can also be often overlaid with corrosion or abrasion resistant alloys to boost their service life.
A Yoke connects the valve body or bonnet together with the actuating mechanism. The top with the Yoke holding a Yoke nut, stem nut, or Yoke bushing along with the valve stem passes through it. A Yoke normally has openings allowing access to the stuffing box, actuator links, etc.. Structurally, a Yoke should be strong enough to stand up to forces, moments, and torque produced by the actuator.
A Yoke nut is undoubtedly an internally threaded nut and it is placed inside the top of the Yoke through which the stem passes. In a Gate valve e.g., the Yoke nut is turned and also the stem travels up or down. In the case of Globe valves, the nut is fixed along with the stem is rotated through it.
Material selection for gate valve bodies runs the gamut, with iron and steel common for larger valves and stainless-steel, forged steel, bronze, etc. acquireable in smaller sizes. Non-metallic options for instance plastic gate valves may also be available. Specifying material to the body generally includes all components being forced, while “trim” means the components independent of the body, like the seats, the disc, the stem, and, if applicable, the bellows. Larger sizes are identified by an ASME class pressure rating and ordered with standard bolted or welded flanges. Sizing a gate valve is easy as the design precludes any significant pressure drop throughout the valve.
Non-rising stem designs are popular where vertical space is restricted – aboard ships, by way of example. Rising stem designs provide a fast, visual confirmation of your valve’s status, the exposed stem could be subject to corrosion. Non-rising stem valves often make use of an indicator to substantiate the gate position. Neither design has much effect on the performance in the actual valve.
Gate valves are routinely automated using electrical rotary actuators, and operation might be sped up together with the use of hydraulic or pneumatic linear actuators. The effort necessary to open and close large gate valves manually could be reduced from the use of geared actuators.