Torque is a force that causes an object to rotate, while tension is a force that causes an object to stretch or elongate. A closer look at the common units of torque, ft·lb (N·m), reveals that torque consists of a force multiplied by a distance. But it is not just any distance; it is the distance perpendicular to the direction of the force between the object’s axis of rotation and the point at which such force is applied.

Leak testing is performed for four basic reasons, says John McLaren, product manager, leak detection at Agilent Technologies, Inc.

• Prevent material loss by leakage
• Avoid contamination of the product or the environment
• Maximize product or system performance and reliability
• Minimize product liability if leakage presents a hazard

All these factors promote improved quality, reduced downtime and lower warranty cost.

A control valve can be used to control pressure, pressure drop, flow and temperature in any system where there is a fluid flowing through a pipe that needs to be controlled. Control valves are commonly referred to as “final control elements,” which convert a signal from the process controller into the desired adjustment to the process. A control valve (with its associated actuator) does this by adjusting the size of its flow passage, based on the signal received.

Many parameters help determine which control valve to select for a given application. The choice, often complicated, can become even more so for control valves destined to handle severe flow conditions.

From time to time Valvemagazine.com likes to re-publish some of our most popular articles from years past. This one was originally published on March 2, 2016.

Normally, valves are pressure tested by the factory to check for leaks before they’re shipped. The type and method of testing conforms to one or more of many different standards. The purpose of these tests and the expected results are often misunderstood and misapplied, resulting in unnecessary delays and unanticipated costs.

This article identifies the most common mistakes. Its primary purpose is to inform and guide end users and engineers that write valve specifications so those parties can avoid some of the mistakes.