A pinch valve is a fluid control device that relies on the principle of flow path constriction to reduce or shut off the passage of material. Most pinch valve designs feature a highly elastic sleeve or insert in the valve body which is gradually constricted or squeezed closed by either air pressure or by mechanical intervention. This method of valve closure is not only effective for controlling clean fluids but also works well for slurries with high concentrations of suspended solids. This is due to the fact that the flexible sleeve is capable of forming an effective seal around trapped particulates which would otherwise jam or block the mechanism of other valve types. Pinch valves are also particularly well suited to flow control applications because of their large operational ranges.
Most valve designs rely on the placement of a solid barrier in the fluid flow path. This is usually a metal gate, ball, or wedge which is either progressively dropped down to close an aperture in the flow path or snaps shut under spring pressure. These valves are well suited to controlling clean fluids but are unable to handle those with high concentrations of suspended solids due to the fact that particulate granules tend to jam the metal barriers. In these applications, the pinch valve comes into its own as one of the most effective solutions for both clean water and slurry suspensions.
Pinch valves generally consist of a metal casing equipped with a manual or electrically driven mechanical gate or a compressed air feed point mounted on the top of the casing. Located inside the casing is a highly flexible sleeve that forms the fluid flow path through the valve. When the valve is actuated, the sleeve is gradually squeezed closed in the center of its length to shut off the flow of fluid. This constriction may be achieved in one of two ways: mechanically or with compressed air.
The mechanical pinch valve is manually operated by turning a handle similar to those on gate valves or electrical motors. In both cases, the handle or motor turns a machine screw that operates the valve mechanism. This mechanism typically consists of two flat metal bars, one on top of the sleeve and one below. When the lead screw rotates, it simultaneously moves both bars closer together, thereby squeezing the sleeve closed as they do so.
Air operated valves feature a shaped chamber that surrounds the sleeve. Compressed air is introduced into the chamber through a solenoid valve and nipple; as the pressure builds in the chamber, it constricts the sleeve until it is totally closed. When the valve needs to be opened, the cycle is reversed, and the air is drawn out, thereby allowing the sleeve to return to its full bore dimensions. Due to the highly elastic nature of the sleeve and the gradual constriction exercised on it, pinch valve designs are well suited to flow control applications which require precise adjustment over a large flow rate range.
