Depending on the nature of the fluid flowing through a pipeline, you must choose one valve or another to manage the fluid along the line. Thus, you can install ball valves, shut-off valves, angle seat valves, butterfly valves and flap valves, among others.
Both the type of valve and the working fluid determine which engineered sealing solution should be chosen to prevent possible leakage episodes. These solutions are based on O-rings, flat gaskets, profiles, graphite formed rings, gaskets and packing, and energized joints.
Index
Sealing solutions for valves with spindles
The valves including spindle are usually of two bodies; that is to say, with an upper part that houses the spindle and a lower part that contains the control element, such as the shut-off valve, the ball, the lentil, etc. The union of the two bodies requires a sealing gasket which, in this case, is a flat gasket. The materials for this gasket can be:
- Silicone (VMQ)
- Rubber nitrile (NBR)
- Fluoroelastomer (FPM)
- Viton®
- Graphite
- Graphite with expanded metal insert
- Restructured PTFE Gylon®
In spindle valves, the engineered sealing solution along the valve spindle or valve stem is typically braided packing or formed graphite rings. And if the valve is manually operated, O-rings are used to seal the stem end to the handwheel.
Sealing solutions for flapper, butterfly and gate valves
At flap valves (or anti-return), butterfly (or lentil) and in gate valves (The sealing of the fluid retaining element is also a problem. The sealing is carried out with an extruded profile that is mounted on the damper guide and on the perimeter of the lentil. The profiles for the lentils are usually T-shaped, while the profiles for the dampers are D-shaped. EPDM and when a higher chemical resistance is required, a fluoroelastomer (FPM) o Viton®.
Another engineered sealing solution for valves are the PTFE energized gaskets with bronze or graphite filler. PTFE is a thermoplastic with no recovery, i.e. it has no memory. Hence the need to “energize” it with a spring or a spring, whose tension opposes the deformation exerted by the housing walls on the PTFE. In a ball valve, energized seals are responsible for sealing between the static part (metal seat on which the ball rests) and the dynamic part (ball) and can also be used for stem sealing.
The chemical resistance of PTFE is well known; however, its mechanical properties can be improved. The material PEEK also has a high chemical inertness and, in addition, offers higher mechanical strength. In a service of high mechanical stress, an energized gasket made of PEEK offers better performance than the same PTFE gasket, as long as chemical attack does not occur.
Another application of PTFE materials and PEEK is the machining of ball seats to replace metal seats in situations where corrosion is a risk factor.
In cryogenic valves, polyethylene (UHMW-PE), due to its excellent behavior at low temperatures and high resistance to abrasion.
In future articles we will describe in more detail the engineering solutions for valve sealing. If you would like more information on these materials, call us at 938 633 277 and we will study together the most appropriate solution to your problem. Get to know all our engineered sealing solutions at our catalog.