The selection of the right valve seat material is crucial to ensure the valve's sealing and performance.
This analysis is part of the set of technical contents that we have already dedicated to valves, where we review solutions from valve sealing to use of certified O-rings for valves and the behavior of resistant elastomers in aggressive fluids.
In this article we review the materials most commonly used in valve seats, explaining their mechanical, chemical and thermal properties, as well as the technical selection criteria according to applications.
Index
Valve seats according to valve type
It is a key part in the sealing of a valve. Its function is to ensure that the fluid does not leak through the base of the valve plug and that the movement of the plug is uniform and without excessive wear. Let's see examples of valve seats:
Valve seats in ball valves
The ball valve employs a spherical plug that rotates on its vertical axis. In this design, the ball rests directly on a part known as a “seat”, which acts as a guiding surface during the ball rotation maneuver, in the opening and closing of the valve.
The materials most commonly used in valve seats (especially in ball valves) are:
- Virgin PTFE, The seals are used in many applications in conjunction with PTFE seals. In many applications these seats work in conjunction with PTFE seals.
- PTFE with fillers, which improves wear resistance and mechanical stability.
- UHMW-PE, suitable for its high resistance to abrasion.
- PEEK and POM, mainly used when higher mechanical strength is required.
Valve seats in piston valves
In piston valves, the plug moves longitudinally and comes into direct contact with the seat when the valve opens or closes. In contrast to ball valves, there is no continuous rotary movement here, but rather a repeated axial support that requires a higher dimensional stability, a good compressive strength and the ability to maintain geometry even under high mechanical loads.
The same technical materials commonly used for valve seats are used here, as they are well suited to the mechanical and chemical requirements of this type of seal. Each brings different advantages depending on the design requirements:
- Virgin PTFE very high chemical resistance, which facilitates watertightness.
- PTFE with fillers improves mechanical strength and reduces creep, which is particularly important when the piston is subjected to repeated axial loads.
- The UHMW-PE is useful in cryogenic valves where impacts or abrasive conditions may occur, always within its working temperature range (-200 °C ... +80 °C).
- PEEK and POM are suitable when the valve operates at high pressures or requires high dimensional stability, conditions in which these materials better maintain their mechanical integrity.
Selection of materials according to the application
The choice of a type of sealing material or the other will depend on the specific service conditions. Temperature, pressure, fluid type and regulatory requirements determine seating behavior and determine which technical polymers offer reliable and long-lasting performance.
The main criteria are described below based on three common scenarios: cryogenic applications, non-cryogenic applications and use in the food industry.
Valve seats for cryogenic applications
In cryogenic applications, the material must maintain mechanical stability and elasticity at extremely low temperatures. The polymers most commonly used in these conditions are PTFE, UHMW-PE and PEEK.
PTFE retains its low coefficient of friction even in extreme cold, which promotes reliable sealing despite thermal shrinkage. UHMW-PE provides higher mechanical strength and good toughness at low temperatures, which is useful when the seat must withstand continuous loads. PEEK, on the other hand, maintains its dimensional stability and rigidity under demanding conditions, allowing it to work at higher pressures.
Valve seats for non-cryogenic applications
In non-cryogenic conditions, temperature and pressure are the most important factors influencing material selection. For applications up to approx. 80 °C, the UHMW-PE is suitable because of its high abrasion resistance and its good chemical inertness. However, above this temperature it begins to soften, which limits its use.
The Virgin PTFE is still a very popular option because of its chemical inertness and its low coefficient of friction; and when it incorporates fillers (e.g. glass fiber or PEEK) it reduces its creep, improves its wear resistance and better adapts to more demanding conditions.
Valve seats for the food industry
Food applications require the seat material to be suitable for food contact and therefore must comply with Regulation (EC) No. 1935/2004 or be FDA certified, both of which guarantee safety in contact with food. In this area, materials such as Virgin PTFE, the PTFE with fillers and the UHMW-PE food grade are common, as they offer a high chemical inertness, thermal stability and absence of migration of formulation components into the food product.
When the pressure conditions are high or is a additional mechanical strength, variants of PEEK specifically formulated to comply with food industry regulations.
In conclusion, the correct selection of the seat material is decisive to ensure the tightness, durability and performance of the valve. Properly evaluating each application and selecting the most suitable material optimizes operation and reduces maintenance costs.
In combination with sealing gaskets, PTFE gaskets, NBR gaskets, FKM gaskets, etc. o Viton gaskets, the valve seats play an essential role in the reliability of any industrial system.
Do you want to know the most suitable seat material for your application? Our technical equipment can help you analyze the service conditions and select the most reliable sealing solution according to your needs.
