Choosing the Right Swagelok Valves for the Job: Part 1

Even for a task as simple as "on" or "off," Swagelok offers a lot of choices

The wide selection of valves offered by Swagelok may seem overwhelming at first: ball valves, needle valves, check valves, safety valves and more. This is the first of a series of posts on selecting the proper valve for the job. In this post we'll look at the various valves used for the most basic on-off functions.

• The most common valve for the job is a ball valve. A metallic ball sits in the path of flow. The ball has a large hole drilled horizontally through the center. When you turn the valve so that the hole lines up with the path of flow, it lets the fluid flow. Give the ball a quarter-turn and the flow stops. Ball valves get the job done quickly, and the position of the handle makes it easy to see whether the valve is open or closed.
• Gate valves are used most often for process control, particularly for lines larger than two inches. Some can be larger than 100 inches. A sealing mechanism -- the "gate" -- sits in the flow path. Rotating or raising the handle raises the gate and lets the fluid flow. The stem going from the handle into the valve might have packing such as gaskets or O-rings to prevent leaks, or it may have "packless" metal-to-metal seals.
• Diaphragm valves are packless and good for fast shutoff and precise actuation speeds. Each valve has a thin diaphragm of metal or plastic that flexes up and down to create a seal over the inlet. They are typically used in high-purity applications such as biopharmaceutical and semiconductor manufacturing. Diaphragm valves are usually small, with internal pathways of 2 inches of less, but they provide the highest cycle life among all valve types.
• Bellows valves have a welded seal dividing the lower and upper halves. The stem is encased in a metal bellows, which seals the inlet by moving up and down without rotating. Bellows valves are packless, making them a good choice when it's critical to have a good seal to the atmosphere and you have limited access for maintenance. Bellows valves are often specified for the containment area in nuclear power plants.

Check back for Part 2, in which we'll look at the valve types best suited for:

• Flow control
• Directional flow
• Overpressure protection

Additional resources

• Valve Sizing Technical Bulletin
• Matching Valve Type to Function: A Tutorial in Valve Selection
• Valve Selection Worksheet