Thursday, February 27, 2020

Cavitation in Valves

Cavitation in Valves

Cavitation can occur in valves when used in throttling or modulating service. Cavitation is the
sudden vaporization and violent condensation of a liquid downstream of the valve due to localized low pressure zones. When flow passes through a throttled valve, a localized low pressure zone forms immediately downstream of the valve. If the localized pressure falls below the vapor pressure of the fluid, the liquid vaporizes (boils) and forms a vapor pocket. As the vapor bubbles flow downstream, the pressure recovers, and the bubbles violently implode causing a popping or rumbling sound similar to tumbling rocks in a pipe. The sound of cavitation in a pipeline is unmistakable. The condensation of the bubbles not only produces a ringing sound, but also creates localized stresses in the pipe walls and valve body that can cause severe pitting.
Cavitation

Read this white paper, courtesy of Val-Matic, to fully understand what happens when cavitation occurs in valves.

Table of Contents
  • Introduction
  • Cavitation Analysis
  • Cavitation Data
  • Valve Coefficient Data
  • Example Application
  • Conclusion & Recommendations
  • References
For question about the proper applications of valves, contact Automatic Controls of Virginia. Call them at (804) 752-1000 or visit their web site at https://acva.com.

Thursday, February 13, 2020

Basics of Industrial Valves and Actuators


This video provides a basic understanding of industrial valves types, and also an understanding of valve actuator types.

Industrial valves are designed in three major categories. They are:
  • Rotary multi-turn valves. These include gate, globe knife and multi port valves. 
  • Rotary quarter turn valves these include butterfly ball plug and choke valves.
  • Linear valves. These include gate, angle globe, and globe valves. 
There are many varieties and subcategories for these basic three design configurations.

Two major functions of industrial valves are isolation and control. Isolation valves are used in applications where the primary concern is the opening or closing of the valve when needed. Isolation valves provide tight shut off and sometimes provide simple control. They are operated via hand wheels or levers, electric actuators, pneumatic actuators, or hydraulic actuators.

Control valves are used to modulate flow to maintain a certain set point in the process control loop. Traditionally, control valves use pneumatic diaphragm positioners, but newer technology enables control with pneumatic and electric actuators.

There are three types of valve actuators:
  • Electric
  • Pneumatic
  • Hydraulic 
Electric actuators use electricity is their power source, have a relatively slow strokes speed, are moderately priced, and typically include the valve operating system. Electrical and mechanical technical skills are required to install and maintain electric actuators.

Pneumatic actuators use air or gas as their power source, have relatively fast stroke speeds, are relatively inexpensive, and require external devices for their valve operating system. In most cases, only mechanical technical skills are required to install and maintain pneumatic actuators.

Hydraulic actuators use hydraulic fluids as their power source, have fast stroke speeds, are more expensive, and require external devices for their valve operating system. Electrical and mechanical technical skills are required to install and maintain hydraulic actuators.

For more information about industrial or municipal valves, actuators or control systems, contact Automatic Controls of Virginia. They can be reached by calling 804-752-1000 or visit their website of https://acva.com.