Wednesday, August 20, 2014

Ball Valves for Industrial Applications

industrial ball valve
Large industrial ball valve
(courtesy of MOGAS)
Perhaps the most universally used type of valve, ball valves come in a wide variety of sizes, materials, pressure classification, port configurations and end connections. They are applied in a multitude of industrial applications, and in every industry from chemical processing, to pulp and paper to food processing to bio-research.

A ball valve belongs to the quarter-turn family of valves, which means its rotational motion is 90 degrees to fully open of close the valve, allowing or stopping flow. Flow through the valve is accommodated by a sphere, or ball, with a hole through it. The ball is sandwiched between two seating rings, usually made of teflon or other elastomer. When the hole in the ball has its axis parallel to the valve ports, you have flow, when the hole is perpendicular, the flow is stopped.

Ball valves bodies come in many different configurations. Most common are:
  • Top Entry Ball Valves: Top entry valves allow for valve service be removing the valve "bonnet" and thus the stem , ball and seats. This design provides a serviceable valve that does not have to removed from the piping.
  • Split Body Ball Valves:  Split body, as their name indicates, consist of a two-part body. One side of the body is smaller than the other, and when separated, allows access to the ball and seating rings.
Ball valve bodies come in many materials, but primarily carbon steel, stainless steel and brass. Depending on the erosive or corrosive nature of the application, or on operating pressures and temperatures, more exotic alloys such as  Hastelloy, Monel, and Inconel may be used.

Ball valves are available with soft (non metallic seats) such as PTFE, RPTF, PEEK and Nylon and "metal" seats usually made from Stellite with graphite seals. Metal seated valves are preferred for high pressure and high temperature applications.

The valve ball is normally some stainless steel alloy, carbon steel, Inconel, Monel, or Alloy 20. Balls can be coated or plated with hard Chrome, Stellite, Chrome Carbide, or Tungston Carbide.

Ball valve end connections include screwed (NPTF thread) and flanged ends (R.F. flanged and ring joint flanged), socket weld end, butt weld, and wafer body.

Ball vales come in several porting arrangements. Most common are: 2 way valves; 3 way, 2 port; 3 way 3 port; and 4 way 4 port.

The advantages of ball valves are they provide a very good leak-tight service, can be quickly closed or opened using reasonable amounts of torque, they are small and comparatively light, and they are available in many different pressure classes, materials, porting arrangements, ball configurations and seating configuration.