a technical knowledge base for all the process piping professionals around the world...
Manual Valves are those valves that operate through a manual operator (such as handwheel or handlever). Manual valves are primarily used to stop and start the flow (block or on-off valves), although some designs can be used for basic manual throttling. The best manual valves for on-off services are those...
Often when commissioning or troubleshooting automatic control valves, there’s a discovery that the control valve, even though fully closed, doesn’t fully shut off the flow of process fluid through the plug and seat. Although closed, there is an “allowable leakage rate” as part of each control valve’s specification. Industry standards...
Rangeability of a control valve is defined as the ratio of maximum to minimum flow that can be acted upon by a control valve after receiving a signal from a controller. Today’s control valve applications often require a degree of high rangeability, i.e. require a valve to control a flow...
Flow Characteristic describes the relationship between the valve coefficient (Cv) and the valve stroke. Each throttling valve has a flow characteristic. As a valve opens, the flow characteristic allows a certain amount of flow through the valve at a particular percentage of the stroke. Flow characteristic allows the valve to...
The Valve Coefficient (also known as Flow Coefficient) of a valve is a relative measure of its efficiency at allowing fluid flow. It describes the relationship between the pressure drop across the valve and the corresponding flow rate. Mathematically the valve coefficient Cv (or flow capacity rating of valve) can be expressed as: where: Q is the rate of flow...