These Swagelok Valves Get the Job Done Without Packing
by Katie Dennis, on Thu, May 22, 2014 @ 16:05 PM
Swagelok’s bellows valves and diaphragm valves perform reliably under tough conditions
A sample of the metal
Most valves have packing of nylon or other material to form a seal between the valve stem and the bonnet. As the stem slides through the seal over and over, however, there's potential for the packing material to widen a bit, creating the potential for a gas to leak out. Gas is the most difficult fluid to seal. So there are some applications where you want to get the same job done in another way. Edmonton Valve and Fitting carries two types of Swagelok valves that fall into this category: bellows valves and diaphragm valves.
Imagine a piece of metal flex hose, an accordion, or a flexible drinking straw. Swagelok puts the same kind of accordion bellows inside the valve, above the stem. Swagelok compresses the bellows and seals the top and bottom with either a weld or a gasket. A liquid or gas can enter and fill the bellows, but because it is sealed at the ends, the fluid can't go anywhere.
Of course you need to turn the handle to screw the valve down. But only the top part of the stem rotates. A swivel joint below that point converts the rotary motion of the stem to linear, up and down motion.
Swagelok makes several kinds of bellows valves. The B Series can have either a gasket seal or a weld. It's good up to 1000 psi as well as for vacuum service, and is rated to perform from -100F to 900F. The U Series is the Cadillac of bellows valves. It too has the bellows assembly capped by either gaskets or welds. In addition, it has secondary packing of either Teflon or Grafoil as a backup in case the bellows ever were to rupture. The U Series is good for 2500 thanks to Acme power transmissions threads. It is rated to work at minus 325F.
Bellows valves can accommodate a high vacuum, and are a good choice for handling hazardous, toxic or corrosive gasses, where a leak can cause a lot of problems. These valves are extremely suited to gas applications.
Instead of using bellows, Swagelok's DL and DS Series diaphragm valves use a stainless steel diaphragm or wafer between the body and the bonnet. The wafer, or diaphragm, fits into a stepped shoulder inside the valve body. When the bonnet is screwed into the body, the stepped shoulder will crunch down creating a seal. You get all-metal containment.
Want more information? We've got the B Series and U Series catalogues available for download here.