A Guide to Ball Valves
A ball valve is a type of quarter-turn valve that uses a hollow, pivoting, perforated ball to control flow through it. When the ball’s hole is in line with the flow it is considered open, and when the ball is pivoted 90-degrees by the valve handle it is considered closed. The handle is flat in alignment with the flow when open, and perpendicular when closed, making it very easy to visually confirm the status of the valve. Ball valves are highly durable and reliable, performing well even after many cycles and closing securely even following long periods of extended use. Both of these qualities make them ideal for shut off and control applications, where they are often preferred to gate and globe valves.
The versatility of ball valves, in addition to their ease of operation and maintenance, makes them well-suited to extensive industrial uses, where they support pressures up to 15,000 psi and temperatures in excess of 750°F, depending on their design and materials. Ball valves sizes can range from 0.2 inches to 4 feet. The valve body can be made from metal, plastic, or metal & ceramic, and the floating balls are often chrome plated to make them more durable.
A disadvantage of ball valves is that they tend to trap water in the center cavity while in the closed position. If allowed to freeze, this water can expand as it turns to ice, cracking the sides of the valve from within. To prevent this, many ball valves utilize some type of insulation or heat tape. Another way to prevent this is to use a freeze tolerant ball valve, which incorporates a special type of plug that ruptures if it freezes. This means that the plug alone will break, rather than the whole system, making for easier repairs.
In general, there are five body types of ball valves: single body, three-piece body, split body, top entry, and welded. The valve operation is the same in every type, and the differences are based on the way the pieces of the valve, particularly the casing that contains the ball, are designed and assembled. There are also different styles dependent on the bore of the ball mechanism itself, and ball valves can be further classified based on their working pressure. Ball valves with working pressures between 3,000 and 7,500 psi are considered high pressure valves, though some highly specialized ball valves can withstand up to 15,000 psi.
Ball valves of up to 2 inches come in single-, two-, or three-piece designs. Single-piece ball valves are inexpensive and typically throw-away. Two-piece valves can be repairable or throw-away. The three-piece design is the most complex, allowing for the center part of the valve, which contains the ball, stem, and seats, to be removed from the pipeline. This fosters efficient cleaning of any deposits, replacement of seats and gland packings, and polishing small scratches on the ball, all without removing pipes from the valve body. Three-piece valves are designed to be repairable.