Example of a double union PVC ball valve.
PVC (PolyVinyl Chloride) ball valves are widely used plastic shut off valves. The valve contains a rotatable ball with a bore. By rotating the ball a quarter turn, the bore is inline or perpendicular to the piping and the flow is opened or blocked. PVC valves are durable and cost efficient. Furthermore, they can be used for a wide variety of media, including water, air, corrosive chemicals, acids and bases. Compared to brass or stainless steel ball valves, they are rated for lower temperatures and pressures and have a lower mechanical strength. They are available with different piping connections, such as solvent sockets (glue connection) or pipe threads. Double union, or true union valves, have separate pipe connection ends that are fixed to the valve body by a threaded connection. The valve can easily be removed for replacement, inspection and cleaning.
PVC stands for PolyVinyl Chloride and is after PE and PP the most used synthetic polymer. It is produced by the reaction of 57% chlorine gas and 43% ethylene gas. Chlorine gas is derived by electrolysis of seawater, and ethylene gas is obtained by distillation of crude oil. In comparison with other plastics, PVC production requires significantly less crude oil (PE and PP require around 97% ethylene gas). Chlorine and ethylene react and form ethanedichlorine. This is processed to yield Vinylchlorine monomer. This material is polymerized to from PVC. Finally, some additives are used to alter properties such as hardness and elasticity. Because of the relatively simple production process and large availability of the raw materials, PVC is a cost-effective and relative sustainable material in comparison with other plastics. PVC has a strong resistance against sunlight, chemicals and oxidation from water.
U-PVC, or PVC-U, is an abbreviation of unplasticized Polyvinyl chloride. The material is also called rigid PVC. When PVC is mentioned as valve housing material, this is in fact always unplasticized PVC. U-PVC doesn’t contain phthalates, these are only used for flexible PVC.
CPVC, or chlorinated PVC, has a higher heat resistance and can therefore be used for hot water. CPVC is obtained by chlorination of PVC. An aqueous solution of PVC particles is chlorinated and exposed to UV light. The chlorine content is increased to 67 percent. CPVC is more expensive than regular PVC and therefore only used in niche applications, such as water heaters.
The list below gives a general overview of important characteristics of the material:
PVC has a relatively low softening and melting point. Therefore, it is not recommended to use PVC for temperatures above 60 degrees Celsius (140°F).
PVC valves are used intensively in water management and irrigation. PVC is also suitable for corrosive media, such as sea water. Moreover, the material is resistant to most acids and bases, salt solutions and organic solvents. In applications where corrosive chemicals and acids are used, PVC is therefore often chosen above stainless steel. PVC has also some disadvantages. The most important drawback is that regular PVC cannot be used for media temperatures above 60°C (140°F). PVC is not resistant to aromatic and chlorinated hydrocarbons. PVC has a lower mechanical strength than brass or stainless steel, and therefore PVC valves have often a lower pressure rating (PN16 is normal for valves up to DN50). A list of typical markets where PVC valves are used:
Special PVC ball valves can be driven by an electric or pneumatic actuator. These valves have a flange to mount the actuator. In general, the flange is dimensioned according to the ISO 5211 standard. Valves with an ISO-5211 flange are often referred to as “ISO-Top”. When selecting an actuator, it is important to check if the valve and actuator have the same flange size. Within the ISO 5211 standard, a range of flange sizes exist such as F03, F04, F05 and F07. More information about the different sizes can be found here. Another important parameter to select the right actuator is the operating torque of the valve. Please note that the exact values depend on multiple factors, such as medium type and pressure. Furthermore, values can vary between manufacturers. An overview of PVC ball valves with ISO-top.
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