Ball Valve Products

A Ball Valve is among the most common valves in the chemical process industries. A ball valve features a rotating ball with a hole through it. When the valve is positioned so the hole aligns with the piping, the valve is open, permitting flow. Rotating the valve 90 deg. closes the valve and shuts off flow. A ball valve is a “full-port” valve, which means that the inner diameter of the valve (the hole in the ball) is the same as the diameter of the pipe in which it is installed. This results in negligible flow restriction.

The simple movement of a rotating ball against a seal makes the valve easy to turn. A ball valve is fairly good at throttling flow, but it is not always the best choice. Because a ball valve is a quarter-turn valve (i.e., it turns only 90 deg.), making very fine flow adjustments can be difficult. Replacing a standard ball that has a straight-through-hole with one that has a special groove cut provides better linear flow control.

In order for the ball valve to function properly, The seal between the moving ball and its seats must be very tight. These parts are made with high precision. If solids are present in the process fluid, they can become lodged between the seats and the ball, causing damage to the ball and increasing the potential for a leak. As a rule of thumb, if the valve is being opened and closed often and the fluid contains abrasive solids, a leak is very probable.

Although most ball valves are two-way valves (Figure 1), three-way valves (Figure 2) are also available. These are used primarily for diverting and blending applications.

When handling sodium hypochlorite, a vented ball should be used. In this design, the ball is vented on one side to allow trapped gases to safely escape from the ball cavity back into the piping system. This prevents pressure from building up in the ball cavity.

Ball valves can be made of various plastics and metals. Sizes typically range from 0.25 in. to 4 in. This type of valve often has unions on each end, making them easy to replace in the field.

Butterfly Valves

Another type of quarter-turn valve is the butterfly valve (Figure 3). When its disc is perpendicular to the flow, a seal is created between the disc and the liner and the valve is closed, preventing flow. When the disc is rotated 90 deg., the valve opens.

The main advantage of the butterfly valve is that it can be installed in very large pipes, in some cases up to 6-ft in dia. Butterfly valves are usually used in pipes larger than 3 in.; they are often not the best choice for smaller pipe sizes. They are installed between two flanges.

Butterfly valves can be further classified as wafer or lug style. The wafer style must be wedged between two flanges and is held in place by the compressive force of the flanges. The lug-style butterfly valve has a threaded body and can be held in place by bolts to just one flange. The wafer style requires flanges on both sides of the valve. Maintenance can be performed on one side of the lug-style valve without shutting down the system on the other side.

The valve has the same inner diameter as the pipe in which it is installed. However, because die disc is directly in the middle of the flow path, there is some flow restriction, and it is not considered to be a full-port valve.

A variety of plastics and metals are used in the construction of butterfly valves. Many designs have a metal body but non-metal wetted parts. Typically, butterfly valves in sizes 8 in. and smaller have a lever-type handle, whereas larger sizes use a gear-operated hand wheel.