Basic engineering devices such as valves contribute to almost every complex system. These mechanical/electromechanical devices regulate media flow and come in dozens of unique varieties; to see all the different types of valves, visit our understanding valves article. The diaphragm valve will be the focus of this article, and we will explore what they are, how they work, and the different types available. Through this investigation, this article should help decide if diaphragm valves could be useful, and how to choose the correct version for a given application.
What are diaphragm valves?
The problem with a standard pneumatic diaphragm valve is that it’s just a single seat valve with an inlet, an outlet and an actuator on it. The diaphragm opens and closes to let flow through the valve. With a lot of valves used in industry, you can have a two-way valve and a three-way valve, so you have a third port inside the valve and the actuator closes one port and opens another.
You can’t do that with a traditional diaphragm valve because it’s only a two-way valve. Bürkert introduced the Robolux valve, which employs two pistons in one actuator to create a three-way type diaphragm valve.
Diaphragm valves use a flexible diaphragm connected to a compressor by a stud which is molded into the diaphragm. Instead of pinching the liner closed to provide shut-off, the diaphragm is pushed into contact with the bottom of the valve body to provide shut-off. Manual diaphragm valve is ideal for flow control by offering a variable and precise opening for controlling pressure drop through the valve. The handwheel is turned until the desired amount of media is flowing through the system. For start and stop applications, the handwheel is turned until the compressor either pushes the diaphragm against the bottom of the valve body to stop flow or lifts off the bottom until flow is able to pass through.
Diaphragm Valve Function
The weir-type design is the most popular type of diaphragm valve and it is best for general use applications or for tough corrosive and abrasive services. They are best used to control small flows. The body of the weir-type has a raised lip that the diaphragm comes into contact with. Weir-type valves use a smaller diaphragm because the material does not have to stretch as far. The material can be heavier so the valve can be used for high-pressure and vacuum services. The weir design is composed of a two-piece compressor component. To create a relatively small opening through the center of the valve, the first increment of stem travel raises an inner compressor component that causes only the central part of the diaphragm to lift instead of the entire diaphragm lifting off the weir when the valve is opened. Once the inner compressor is opened, the outer compressor piece is lifted along with the inner compressor and the additional throttling is similar to the throttling function in other valves. Weir-type bodies have bonnet assemblies recommended for handling dangerous liquid or gas because if the diaphragm fails the hazardous materials will not be released into the surrounding system. They are also recommended for food-processing applications because the body is self-draining.