Valve Classification According to Port Size

1. Full-Port Valves

In process systems, most valves are designed to restrict the flow to some extent by allowing the flow passageway or area of the closure element to be smaller than the inside diameter of the pipeline. On the other hand, some gate and ball valves can be designed so that internal flow passageways are large enough to pass flow without a significant restriction. Such valves are called full-port valves because the internal flow is equal to the full area of the inlet port.

Full-port valves are used primarily with on-off and blocking services, where the flow must be stopped or diverted. Full-port valves also allow for the used of a pig in the pipeline. The pig is a self-driven or flow driven mechanism designed to scour the inside of the pipeline and to remove any process buildup or scale.

2. Reduced-Port Valves

On the other hand, reduced-port valves are those valves whose closure elements restrict the flow. The flow area of that port of the closure element is less than the area of the inside diameter of the pipeline. For example, the seat in linear globe valves or a sleeve passageway in plug valves would have the same flow area as the inside of the inlet and outlet ports of the valve body. This restriction allows the alve to take a pressure drop as flow moves through the closure element, allowing a partial pressure recovery after the flow moves past the restriction.

The primary purpose of reduced-port valves is to control the flow through reduced flow or through throttling, which is defined as regulating the closure element to provide varying levels of flow at a certain opening of the valve.