There are many types of valves and can be categorized into a number of basic types. If you group them according to how they are actuated, you will have five types; solenoid valve, motor, pneumatic valve, hydraulic and manual valve. Valves are made up of components that enable them to carry out their functions. Such components include disks, seats, stems, bodies, bonnets, ports, handles, valve balls, springs, trims and even gaskets.
What are severe service valves? When we asked CGIS, a well known name in the industry of severe service valves they told us: “These are simply control valves used in severe service conditions. By partially or fully opening control valves you can be able to regulate flow, temperature, pressure and liquid levels. They are widely used in hydrocarbon, power, pulp, and paper or chemical industries.”
Sizing calculations are performed to identify this control valve. Some of the information required for such calculations includes vapor pressure of liquids; temperature valve size; flow rate, upstream pressure and differential pressure at maximum, normal and minimum; fluid state. If a control valve does not violate the calculated threshold, it fails to be classified as an SSCV but rather a general purpose control valve.
An SSCV is selected depending on the threshold value. This is not done by anybody but rather experts/suppliers who have an insight in SSCV trims and features and major in controlled applications. In most cases the following conditions fall under severe services: compressor anti-surge, turbine by-pass, autoclave let-down, engine test stands, toxic/lethal service, boiler feed water, fluid with high outgassing potential, slurry control, choke valves, high-pressure separator drains, solar power molten salt, coal gasification, and minimum flow recycle.
The design of these valves has two flow mechanisms. Radial flow mechanism which is characterized by sudden contraction, small passage friction, surface impingement, direction change, mutual impingement, cavitation bubble isolation, turbulent mixing and sudden expansion. Axial flow is the second flow mechanism and has the following features: sudden impingement, direction change, sudden contraction and sudden expansion.
Examples of these valves include:
Cavitation control – curb the harmful effects of cavitation
Aerodynamic nose control – reduce noise compressible flows
Steam conditioning – regulate superheated steam to give the desired output
Engineering solutions – custom engineered for specified functions
However, since there are no national or world standards of identifying these valves, there is a risk of having a mix-up. This poses a major risk for those handling those valves due to counterfeit products. The ordinary worker is therefore placed in a precarious position. It is, therefore, imperative to work hand in hand with certified expert in both the supply and installation of these valves. When correctly identified and installed, the user grips many benefits such as saving workers’ lives and protecting our environment.