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Valve Selection and Purchase

Valve selection is a major activity of a epc project cycle which begins as early as FEED(front end engineering and design) phase of a project where P&ID’s are designed. P&ID forms the basic document for initiation of valve selection and purchase phase .The P&IDs are designed on a system approach usually which show all major equipment, interconnecting piping, and the required valves.FEED engineer or for a large project a specialist engineer for valve also known as Valve Engineer is assigned to the task.

Valve Engineer will be responsible to select the most appropriate valve in co-ordination with process engineers, control system engineers and purchase engineers. Valve engineer will have the sufficient knowledge about the know-how of the proposed system.The top most priority for selection of a valve will be given to process variables.

Valve engineer ,for selection of a valve for a particular system identifies all the process variables from the PFD’s (process flow diagrams).

PFD’s show various process variables which include:
Service
Temperature
Application system identification
Media flow (fluid phase)
Pressure
Flow rates

with these basic inputs ,governing standards and design basis ,a valve engineer filters and selects the most appropriate

  • Size of the valve to accomplish the required flow rate as per process.
  • Type of the valve to be used to ensure the required process constrains are fulfilled for a particular system.
  • Location of the valve in plant layout to ensure that all instrumentation and schematic layout of equipment is suitable for the proposed system design.
  • A Valve engineer also prepares a material take-off indicating the piping class, valve,size,type of each valve which evolve to form a master valve-list.

    • Notes:

  • The development of physical piping layout or a 3D-model of plant later in detail design phase may require the revision (changes) to the selection of valve based on layout requirement or purchase order accepted deviations or change of process variables.
  • Master Valve List will later used to designate valve tag numbers,and valve data sheets by a specification engineer in detail design phase.
    • The cost of replacing a valve from service is far more than the cost of valve itself, hence careful selection of valve shall be the utmost priority of the specification engineer.