As a continuation of the series of articles about valves published in our blog “Some valve sealing solutions”.”, “Certified O-rings for valves.“ y “Elastomers resistant to aggressive fluids in valves”.”, In this new article we will take a closer look at another aspect of valves, in which we will explain what materials you should consider when choosing valve seats.
Index
Examples of valve seats
Ball valve
For example, in a ball valve, the control element (ball) rests on the seat and rotates on the seat when the valve is opened or closed. The ball seat material must have a chemical resistance in accordance with the process fluid as well as temperature resistance, among other requirements.
Piston valve
Another type of valves that use seats are those whose closing element is a piston. In the piston valve, when the valve opens, the piston moves back and rests on the corresponding seat.
Both in the ball valve and in the piston valve, in both cases, the valve seat must guarantee the tightness of the valve and prevent wear due to metal-to-metal contact and for this purpose, seat geometries are usually concave for balls and more complex in shape for pistons.
Sealing materials for valve seats
Valve seat material options available are:
- - Technical plastics Virgin PTFE.
- - PTFE with fillers.
- - UHMW-PE
- - PEEK y POM, although these are more common in parts subjected to high mechanical stresses such as bearings and guide rings, for example.
For low temperature cryogenic services
The alternatives are restricted to PTFE, PEEK y UHMW-PE. These last two engineering plastics have a compressive ultimate load and a breaking load significantly higher than that of the PTFE, however, the PTFE is softer and more elastic. In addition to the mechanical aspects, chemical compatibility with respect to the working medium must be taken into account when choosing one material or another.
For non-cryogenic applications
Up to a temperature close to 80 ºC for non-cryogenic applications, the UHMW-PE can be a good choice because of its high abrasion resistance and good chemical inertness. However, it is not recommended for use at temperatures above 80 ºC because it begins to soften.
Technical plastic PEEK has in its favor that it has good mechanical properties, good chemical resistance and a wide range of working temperatures. On the downside, it should be noted that it is a very hard material with low elasticity. Both PEEK like POM is recommended when the service pressure is very high.
Finally, the Virgin PTFE is a very popular material for seat valves due to its very high chemical inertness and low friction coefficient. In addition, with the addition of glass fiber or PEEK, some of its properties are improved.
For the food sector
In the event that a certain certification is required, such as food certification, most of the materials presented comply with the certification. FDA and regulation EC 1935/2004.
If you want more information about these materials, please contact us and we will study together the most suitable solution according to your needs. Know all our engineering solutions in watertightness at our catalog.