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Deciding on the right seat material can be a difficult decision when it comes to ball valves because you'll have several options. Determining factors you will need to consider include the materials used in construction, the appropriate size, and the type of design features including V-port, bleed, double bock, 1, 2, or 3 pieces, etc. An even more important consideration is the seat type.

Having a complete understanding of the process conditions should be the starting point when it comes to choosing seated valves. Does your situation require a bubble tight shut off? Is the fluid corrosive? Does it contain abrasive particulates? Will it be under high pressure or temperatures? Once you have a firm grasp on these factors, the choice will be apparent.

.Metal Seated Ball Valves

The key advantage of metal seated valves when compared to soft seated valves is that they can withstand high temperatures and severe service conditions. Metal seats can stand up to extreme flashing, hydraulic shock, abrasive process fluid, and high temperatures up to and exceeding 1,000° F. They are also ideal for high erosion or corrosion applications. Another important factor is that metal seats can be hardened by specialized coatings.

.Soft Seated Ball Valves

Soft seats are typically composed of thermoplastic components like PTFE. These valves are appropriate for applications in which chemical compatibility is crucial, and in situations where having the tightest seal is important. Soft seats, however, aren't suitable for processing abrasive or dirty fluids. These valves are known to break down under conditions like these, resulting in a leaky valve. Complications introduced by soft seated valves are related to the fact that they don't stand up to applications that challenge their service limits. Metal seated ball values on the other hand can hold up under high temperatures and extreme service conditions. Well established in the field, metal seated ball valves deliver uninterrupted service with the maximum shut off standards. The valves also work for longer time periods than soft seated valves. These durable valves can basically handle the majority of abrasive applications.

Installation
The installation of metal seated valves can comply with shut off standards which include ANSI/FCI 70-2-1976 and designed for allowed leakage. The most frequently specified leakage classes include Class V and VI. Class VI is often misinterpreted as "bubble tight." In fact, a certain amount of leakage is permitted, measured by the amount of air bubbles that escape per minute during testing. "Bubble tight" shut-off is more accurately related to resilient-seated valves.