Valves exceed any other piping component. Estimates reveal that a substantial portion, approximately 8-10%, of the total capital expenditure of the chemical process industry is used for the procurement of valves. In terms of the number of units also. Hence, proper thought should be given for the selection of valves. The first step in the selection is to determine exactly what function the valve is expected to perform after it has been installed.
Valves are installed on equipment/ piping to perform any one of the below mentioned functions.
Classification of Valves:
Based on functions:
Functions of Valves
The design of the valves is done in such way as to perform any of the above functions. The type of valves used can be classified in the following categories.
Special Purpose Valve
- Multi-port Valve
- Flush Bottom Valve
- Float Valve
- Foot Valve
- Line Blind Valve
- Pressure / Vacuum Relief Valve
Based on the end connections:
The valves can further be classified based on the end connections. End connection means
the arrangement or attachment of the valves to the equipment or to the piping. The types of
end connections are:
- Screwed ends.
- Socket weld ends
- Flanged ends
- Butt weld ends
- Socketted ends
- Wafer type ends
Based on the materials of construction:
The valves could also be classified based on the materials of construction. There can be any number of combinations possible with the materials of construction. It is for the piping engineer to select the same in consultation with the process engineer to suit the process fluid.
The environment in which the valves are installed is also to be considered for selection of materials of construction. However, the most commonly available materials are:
- Cast Iron
- Gun metal
- Carbon Steel
- Stainless Steel
- Alloy Carbon Steel
- Poly Propylene UHMW-PE,UHMW-HDPE etc
- Special Alloys
Body could also be lined with elastomer so that process fluid will not be in contact with the metal.
The valve could also be classified based on the type of construction. Valve manufacturers offer endless varieties of construction. Based on the operation, valves can be broadly classified as operated valves and self-operated valves. Mainly the check valves are self-operated and all other types come under operated valves.
(Reference: “Selection and Application of Valve – Piping Handbook”)