Plastic Diaphragm Valves
It is important to fully understand the material capabilities of a diaphragm valve as failure to do so could lead to potentially hazardous and costly product contamination and mechanical failure. Plastic valves are often implicated in the transfer of liquid, gaseous and semi-solid process flows including silicones, adhesives, oils, chemicals, water, cleaners, sanitizers, coatings, fuel and more. In many applications the materials are highly corrosive and only specially formulated plastics can be used. A number of different plastics are therefore available to suit process valve needs under any circumstances. PVC provides good flexibility, smooth surfaces and is nontoxic. Similar to this, polypropylene offers the additional benefits of resistance to UV, weathering and ozone exposure. PTFE is suited for use with highly corrosive substances while CPVC maintains integrity in high heat applications such as hot water or molten metal transfer. Each of these acetyl polymers, and others commonly used, offer high fatigue resistance and lubricity which help to increase product longevity. Biopharmaceutical, agriculture, irrigation, plumbing, medical, water treatment, chemical and food processing, pulp and paper, mining and energy production industries employ diaphragm valves with plastic components in their daily operations to start, stop and modify flow rates and pressures manually or through automated actuators.
All diaphragm valves have three main components. The body of the valve is a molded, extruded or die cast cylindrical element that is placed midstream in the plumbing. Although metals are often used for this housing as well as the actuation material it holds, plastics are preferred in many applications. The final component, the diaphragm is nearly always made of plastics. Examples include natural rubber, viton and silicone all of which can be wound, cast, molded or extruded to the exact thickness needed for the valve. The materials must be compatible with the process stream, as well as impermeable. When engaged, the actuator directs the movements of this diaphragm and pushes it towards the opposite side of the pipe, blocking the flow of materials. If shut off is desired, the membrane is stretched to fill the entire diameter of the line. Because elastomers can compress, contact with the opposing pipe wall creates a near leak proof seal. When the valve is opened, the actuator releases the pressure placed on the membrane allowing it to return to its original position. It is the ability of plastics to be repeatedly stretched and relaxed that makes them essential to diaphragm valve systems. In addition to media type and materials, manufacturers should consider temperature and pressure ratings, frequency of operation, diameter and other dimensions, end connections and process stream velocity with regards to the intended application for the valve.
