Control Valves Mechanical Friction Problems
Control valves are mechanical devices with moving parts, and as such they are subject to friction, primarily between the valve stem and the stem packing. Some degree of friction is…
Choked Flow of Control Valves
Both gas and liquid control valves may experience what is generally known as choked flow. Simply put, “choked flow” is a condition where the rate of flow through a valve…
Instruments Calibration Procedures
Calibration refers to the adjustment of an instrument so its output accurately corresponds to its input throughout a specified range. The only way we can know that an instrument’s output…
Relative Flow Capacity of a Valve
The flow capacity of a valve (Cv) is a quantitative rating of its ability to pass a fluid flow for a set of given pressure and fluid density conditions, defined…
Gas Valve Sizing
Sizing a control valve for gas or vapor service is more complicated than for liquid service, due to the compressibility of gases and vapors. As a gas or vapor compresses…
Process Safety and Instrumentation
Here we discuss about instrumentation related to industrial process safety. Instrumentation safety may be broadly divided into two categories: how instruments themselves may pose a safety hazard (electrical signals possibly…
Classified Areas and Electrical Safety Measures
Any physical location in an industrial facility harboring the potential of explosion due to the presence of flammable process matter suspended in the air is called a hazardous or classified…
Inherent vs Installed Control Valve Flow Characteristics
What is inherent characteristic of a valve ? The inherent characteristic of a valve is the characteristic published by the manufacturer, based on tests performed in a system where great care…
Control Valve Performance with Varying Pressure
Now let us consider a scenario where the pressure drop across the valve changes as the rate of flow through the valve changes. We may modify the previous example of…
Control Valve Performance with Constant Pressure
First, let us imagine a control valve installed at the base of a dam, releasing water from the reservoir. Given a constant height of water in the reservoir, the upstream…
