Pinch valves, also known as clamp valves, are designed to control or shut off the flow of abrasive, granular, fibrous, and corrosive media. They are used in applications such as water treatment, sewage disposal and process food handling.
Unlike conventional control valves which have internal passages, orifices and seals that come into direct contact with the media to be controlled, pinch valves isolate these parts of the valve from the fluid transporting media. This prevents the flow media from clogging or contaminating the valve parts with large particulates.
These valves are rated to 5 million or more cycles before they need to be replaced. This means they are a good choice for medical or scientific instruments, or for other environments that require long-term operation and maintenance.
There are two basic types of pinch valves: external and internal. The internal type has an elastomeric rubber sleeve that is fitted into the valve housing. The end connections are screwed or bolted into the sleeve to provide support and connection.
The sleeve should be manufactured of natural and synthetic rubbers and plastics that have good abrasion resistance. This will help to prevent damage to the sleeve by the flowing media, which could then interrupt the flow of the fluid.
In addition, the sleeve should have an air nipple that is located on the outer body of the valve and when the valve is in the closed position, this nipple is pressurized by the pressure from the fluid transporting media inside the valve. When the nipple pushes the valve sleeve down, it closes tightly and effectively locks the valve shut.
A major advantage of this design is that it has very little pressure drop between the inlet and outlet. This makes it ideal for on/off service, as well as throttling services.
The sleeve of the pinch valve is the only part that comes into contact with the liquid or gas flowing through the tube. This means that the material should be lightweight to avoid abrasion.
These sleeve materials can include natural and synthetic rubbers, polyethylene (PE), nylon, PTFE, and other thermoplastics. The material should have good abrasion resistance to minimize damage to the tube from the flowing liquid or gas.
In addition to these sleeve materials, the body of the pinch valve should be made of a lightweight material to allow easy handling and maintenance. The valve body should be manufactured from a material that does not need to be compatible with the liquid or gas it is regulating since the material does not come into direct contact with it.
The sleeve of the pinch can be made from different materials including natural and synthetic rubbers, nitrile (NBR), EPDM, and silicon. The sleeve of the pinch must be manufactured of a material that is flexible enough to open and close without developing a memory or losing its shape, which would inhibit the opening of the sleeve. In addition, the sleeve of the pinch should be made of a material that is corrosion resistant and has high temperature resistance to ensure maximum life.