Industrial Valves

2Valve Sizing

2.1 Introduction

Valve sizing is an essential engineering task that must be done accurately since improper valve sizing is both expensive and inconvenient. If a valve is too small, it cannot pass the required flow and compromises flow assurance and process integrity. On the other hand, an oversized valve increases the cost. Valve sizing is typically conducted based on both theoretical and experimental methods: Valve sizing is split based on the valve's applications, such as isolation valves, nonreturn or check valves, control valves, and safety valves.

2.2 Isolation Valve Sizing

A ball, plug, or gate valve that stops and starts fluids normally has the same size as the pipe it is connected to. A 3″ isolation valve, for example, is typically connected to a 3″ pipe. It is possible for ball valves to have a full or reduced bore, and the bore is defined by the size of the hole inside the ball. Full‐bore ball valves in 3‐in. sizes have a nominal pipe size (NPS) of 3″. Reduced bore ball valves in 3 in. sizes have a NPS of 3″ × 2″. As an example, a 3″ refers to the size of the valve end connected to the piping, whereas a 2″ refers to the size of the valve bore. Engineers intend to use a reduced bore ball valve as a first choice because of its lower cost unless the reduced bore causes flow assurance problems or undesirably very high‐pressure drop. As an example, ball valves on subflare lines which are installed before and after pressure safety valves (PSVs) shall be ...