How do you select the appropriate valve seat hardness and surface finish?

1 Hardness and Wear Resistance

One of the main factors to consider when selecting the valve seat hardness is the wear resistance of the material. The valve seat should be able to withstand the abrasive and erosive effects of the fluid, the pressure and temperature changes, and the repeated opening and closing of the valve. Generally, the valve seat should be harder than the valve plug to prevent excessive wear and leakage. However, the valve seat should not be too hard or brittle, as it may crack or fracture under high stress or impact. A common measure of hardness is the Rockwell C scale, which ranges from 0 to 70. The higher the number, the harder the material.

3 Material and Design Options

There are many types of valve seat materials and designs available, depending on the application and the service conditions. Some of the most common materials are metal, elastomer, plastic, and ceramic. Each material has its own advantages and disadvantages in terms of hardness, wear resistance, surface finish, leakage rate, corrosion resistance, temperature range, and cost. Some of the most common designs are integral, replaceable, soft-seated, and hard-faced. Each design has its own benefits and drawbacks in terms of ease of installation, removal, and repair, sealing performance, durability, and flexibility.

4 Metal Valve Seats

Metal valve seats are made of various alloys of steel, stainless steel, bronze, brass, nickel, titanium, or other metals. They are suitable for high-pressure, high-temperature, and corrosive applications, as they have high hardness, wear resistance, and corrosion resistance. They can also provide a good surface finish and a low leakage rate, depending on the machining and lapping process. However, metal valve seats are also more expensive, more difficult to manufacture and maintain, and more prone to galling and seizing than other materials.

5 Elastomer Valve Seats

Elastomer valve seats are made of rubber or other synthetic polymers that have elastic properties. They are suitable for low-pressure, low-temperature, and non-corrosive applications, as they have low hardness, high flexibility, and good sealing performance. They can also provide a smooth surface finish and a very low leakage rate, as they can conform to the shape of the valve plug. However, elastomer valve seats are also more susceptible to wear, tear, swelling, and degradation than other materials.

6 Plastic Valve Seats

Plastic valve seats are made of thermoplastic or thermosetting polymers that have plastic properties. They are suitable for low to medium-pressure, low to medium-temperature, and mildly corrosive applications, as they have moderate hardness, wear resistance, and corrosion resistance. They can also provide a smooth surface finish and a low leakage rate, as they have good dimensional stability and low friction. However, plastic valve seats are also more sensitive to temperature changes, chemical attacks, and deformation than other materials.

7 Ceramic Valve Seats

Ceramic valve seats are made of inorganic materials that have ceramic properties. They are suitable for high-pressure, high-temperature, and highly corrosive applications, as they have very high hardness, wear resistance, and corrosion resistance. They can also provide a smooth surface finish and a low leakage rate, as they have high compressive strength and low porosity. However, ceramic valve seats are also very expensive, very difficult to manufacture and maintain, and very brittle and fragile than other materials.