material selection on ball valves

A Ball Valve is simple in its design. Used to control flow, the ball at the centre of the valve has a hollow middle section and as you turn a handle, it rotates this ball allowing liquid to enter into the hole, and flow through. Generally speaking Ball Valves are the least expensive option of any valve configuration and require no lubrication and little maintenance. They are relatively versatile in their application and this will have a big bearing on the types of material that are selected.

Soft Seated Ball Valves

The term ‘Soft seated’ generally refers to Ball Valves that use plastics at their base. There are a range of different thermoplastic materials that are used. Some of the most common include:

PTFE- This Teflon material is one of the most commonly specified in sealing applications, one of the major advantages of PTFE is that it has a wide chemical compatibility making it suitable for a wide range of different media, and has a wide temperature range from -45 Degrees Celsius to just over 200 Degrees.

Polyoxymethylene – This plastic is often used in high pressure applications up to 5000 PSI, there is a smaller temperature range for these Ball Valves, but they are more rigid than PTFE. Polyoxymethylene is sold under a number if different brand names and may be referred to as Acetal, Delrin or Polyformaldehyde.

PEEK – PEEK offers excellent mechanical and chemical resistance and is especially suited to high pressure and high temperature applications such as in the Nuclear sector.

Soft Seated Ball Valves are often specified where chemical compatibility is important and where a tight seal is required, they are however not recommended for processing fluids that are dirty or abrasive in nature as they will quickly break down.

Metal Seated Ball Valves

Generally speaking a metal seat will be specified for applications with higher temperatures or more sever service conditions.

Stainless Steel Alloys – Often Specified for Floating Ball Valves, Stainless Steels offer a good level of corrosion resistance. Stainless Steel 316 is able to perform in high pressure environments up to 6000 PSI. 304 is another popular grade of Stainless Steel, it is cheaper but has less chromium content and so may have a shorter part life.

Brass and Bronze – Both Brass and Bronze are Copper Alloys and as such are operate well at high temperatures, they are in the mid-level in terms of cost but can’t operate at high pressures. They are generally stronger than plastics, but not as popular as they once were with their main application now being primarily in plumbing systems.

Coating of Metal Seats

Often to prolong their life and especially in connection with severe service applications, Metal Ball valves will under go a metal finishing process to further insulate the base metal from its environment and prevent corrosion and wear.

Electroless Nickel Plating – ENP provides a high level of corrosion protection and has an advantage in being an autocatalytic process meaning the Nickel itself will act as a catalyst for the plating mechanism. It will deposit evenly on uneven services making it ideal for Ball Valves.

Chrome Plating –  Hard Chrome Plating has often been utilised in the design of Ball Valve Seats but may be coming under threat from increased environmental concerns over the process. Hard Chrome provides a high level of hardness and wear resistance.

Tungsten Carbide – For more severe environments where severe flashing or hydraulic shock is expected, a harder coating will be required. If temperatures are below 150 Degrees Celsius then most often HVOF applied Tungsten Carbide coating will add a high level of corrosion and wear resistance whilst also offering low porosity.

Chrome Carbide – For temperatures up to 815 Degrees Celsius then Chrome Carbide or Cobalt- Chromium alloys should be considered as these will achieve a hardness of 70+ HRC and will provide excellent corrosion resistance.

B&B Precision offer full machining and finishing of metallic Ball seats. We have worked with a wide variety of Valve manufacturers in the full supply, CNC machining and finishing of Stems, Seats, Balls and Gates including our own HVOF coating facilities. We are ISO 9001:2015 accredited and based near Huddersfield, West Yorkshire.


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