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Stainless steel ball valves utilize a machined or soldered spherical ball to block or enable fluid flow. The ball is connected to a stem which in turn is connected to either a handle (for manual use) or a motor for automated use. Turning the stem rotates the ball and either exposes the bore to the fluid path or blocks it. With their superior corrosion resistance and sturdy construction stainless steel ball valves are commonly used for high pressure saline or corrosive media applications. Industrial grade valves are usually rated to 1000 psi or higher. Stainless steel ball valves are either a “trunnion pin” or “floating ball” design. In a trunnion pin design, the ball is held in place by a pin at the base of the valve body. This design is more common for larger valves (greater than 6” in diameter). In a floating pin design, as the name implies, the ball “floats” atop of and is held in place by the valve seats. Some features that differentiate higher quality valves include being cast from a higher grade of stainless (316 vs 304), a stainless steel ball (316 vs other alloys), a solid vs plated steel ball, and high quality sealing materials. Sealing materials can vary by application but reinforced Teflon (RTFE) is commonly used as it provides excellent sealing performance for a wide range of applications and is chemically inert. Air actuators, also called pneumatic actuators, open and close the valve using compressed air. In a scotch yoke actuator, high pressure air acts on a piston which is connected to a slotted yoke As the piston/yoke moves, the yoke engages with a splined shaft (the pinion) to produce rotary motion. Air is controlled by a central valve bank or by a pilot solenoid valve mounted directly to the actuator. Air actuators air available in either double-acting or spring return models. Double acting actuators use compressed air to both open and close the valve, whereas spring return actuators us air to open the valve and compressed springs to return the valve to the closed position. (Alternatively, the valve assembly can be set so the springs return the valve the open position, ie a “fail open” configuration.) Scotch yoke actuators are simple, reliable and lower cost than electric actuators. Their main drawback is they require a source of compressed air which usually makes them unsuitable for field or remote applications. Some features that differentiate higher quality scotch yoke air actuators include a hard-anodized aluminum body, a weatherproof enclosure (usually IP67/ NEMA 4X or higher), and pre-configured mounting points for positioners and solenoid valves.
