Sodium Hypochlorite is inherently an unstable compound. Two things can happen to it in a piping system that will affect the choice of a valve. Sodium Hypochlorite can decompose over time, which results in the formation of crystalline salts, and as it decomposes, one of the decomposition by-products is oxygen gas.

Because they are the most common type of plastic valve, True Union Ball Valves are often used in sodium hypochlorite service. This type of valve may work out fine in some applications, particularly in 2" and under sizes, but in many other they won't.

The main problem with ball valves, especially those over 2" in size, in sodium hypochlorite service is the crystallization problem When the valve is operated, the ball turns and liquid is trapped in the cavity between the ball and the valve body. The trapped sodium hypochloirte starts to decompose and crystal begin to form. The crystalline salts adhere to the surfaces of the ball and seals causing a "freezing" of the valve making it in-operable. When the valve is operated, the torque required to do so, may be greater than the strength of the valve stem causing it to break. But that's just the start of the problem. Now the valve has to be taken out of service to be repaired. If oxygen gas has formed behind the ball it is now pressurized. When the ball is freed up and turned, the pressure of the oxygen gas will blow out any liquid sodium hypochlorite trapped behind the ball.  A dangerous situation.

These types of problems are most likely to occur in valves larger than 2" that are operated infrequently. And also in valves installed at the bottom of tanks where precipitated impurities could get into the valves and cause accelerated decomposition of the sodium hypochlorite.

A plastic, PVC butterfly valve with EPDM or Hypalon seals is often a better choice for sodium hypochlorite services in pipelines 2" and larger. Butterfly valves are less prone to freezing up than are ball valves because of the formation of crystallite salts on the sealing surfaces of the valve. For smaller size pipe lines a plastic diaphragm valve may be a better choice than a ball valve for the same reasons. Remember that all applications are unique and these recommendations may, or may not apply, in all cases. Sodium Hypochlorite is a potential dangerous process media and Material Safety Data Sheets should be consulted for additional information and safety precautions taken before making any determination is made regarding the application.