Diaphragm valves are one of the many flow control devices available on the market today. They offer precision regulation to liquid, gas, and semi-solid slurry flows alike. Diaphragm valves regulate the transport of process streams by sealing process flow lines, either partially or fully, with a flexible membrane that is stretched by an actuator.
Valves may be manual, automatic, pneumatic, electric, or hydraulic. They are reliable and easy to install and maintain, and as such, they have applications in quite a few industries. These industries include agriculture, biopharmaceuticals, chemical processing, energy production, food processing, irrigation, medicine, mining, plumbing, pulp and paper, and water treatment.
Diaphragm valves are separated into two major categories: diaphragm check valves and diaphragm control valves. Diaphragm check valves ensure materials flow unidirectionally, while diaphragm control valves allow manufacturers to modify pressure and flow rates as they go along.
In turn, check valves and control valves are further divided into two configuration groups: seat valves and saddle valves, or straight-way and weir valves, respectively. Seat valves and saddle valves both have two or more ports through which materials flow. With both, one port serves as an inlet and at least one other serves as a place for exhaust to escape. When the valve is not engaged, materials will simply flow in one port and out the other, but when it is, flow becomes restricted or completely repressed. Read More…
The main difference between seat valves and saddle valves deals with the alignment of their ports. Specifically, seat valve bodies use a 90° bend to cause the directional change of a process stream as it moves around a corner. Saddle valves, on the other hand, direct flow with two ports that are located opposite one another. Essentially, seat valves create a nonlinear stream path, while saddle valves create and regulate a linear one. Most often, seat valves are used to facilitate angled flow in cistern or tank bottoms, while saddle valves mainly assist pre-existing flow lines.
Aside from the difference in piping or tubing angle, seat valves and saddle valves are essentially the same. To begin with, they both consist of a spherical or cylindrical body, attached to the tubing or tank that requires the valve, which contains the actuation device and diaphragm. They both also have the same type of diaphragm.
The diaphragm of both is thin at the edges and thick in the middle, a feature that permits easy stretching. It lifts up when the valve is opened, allowing for gases or fluids to pass. When the valve is closed, the diaphragm is engaged by the pressure of a rod or piston, called a stem, and moves towards the opposite wall of the piping to create a flexible but effective flow barrier.
Actuation devices may be used with pneumatic, hydraulic, manual, or electric controls. Among automated diaphragm valves, pneumatic controls are the most common, because they only require the compressed air to expand and contract the diaphragm materials. Something to note about the actuator is the fact that it boosts the capabilities of clean valve operation because of the broad possibilities they offer. Clean valve operations are important to many of the applications for which diaphragm valves are used, and so many of them require enhanced valves, such as hygienic valves, biotech valves, or sanitary diaphragm valves.
All of these help them avoid product contamination. Zero static valves are another diaphragm valve type that are great for clean operations, because they eliminate the opportunities of bacterial growth and flow stagnation. Also useful are plastic and stainless steel diaphragm valves, which are commonly employed by the chemical, food processing, and medical industries.
Speaking of plastic and stainless steel, the materials of which a diaphragm valve is made must be chemically compatible with the material flowing through the valve and they must be durable. If it is not, it will likely sustain damage that can lead to product contamination. Materials and compositions they may encounter include, among others: adhesives, chemicals, cleaners, coatings, colorants, fuel, paints, silicones, and water. Diaphragm valve bodies are most often made of materials such as brass, cast iron, CPVC, PVC, stainless steel, and steel.
Also, to reduce friction and increase product longevity, manufacturers have the option of adding a body lining of a fluorine plastic or rubber. The actual diaphragm is made of various elastomers, like polyethylene and polypropylene, and others like those used to line the valve mechanism. If the diaphragm will encounter highly abrasive materials, it can be reinforced with mesh fibers.
Before purchasing a diaphragm valve, customers should consider factors such as projected space and application diameter and dimensions, frequency of operation, media type, temperature and pressure ratings, process stream velocity, and required end connections.
Help can be found with a valve manufacturer or supplier. After purchasing the valve, it is equally important that customers properly install their valve. Doing so ensures efficiency and a lack of leakage. Finally, to maintain the health of their diaphragm valve, customers must conduct routine cleaning and maintenance.