An informational blog dedicated to the application of industrial controls, valves and valve automation in the municipal, environmental and industrial markets. This resource will provide educational information in the form of new product introductions, application notes, and basic concepts of all things related to instrumentation, process control, industrial valves, valve actuation, and flow control. Courtesy of Automatic Controls of Virginia (ACVA).
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.
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.
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.
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.
Pinch valves are designed and constructed to outlast other types of valves in high wear applications. They are ideal where shut-off and control applications involve abrasive or corrosive slurries, powders or coarse substances.
PINCH VALVE OPERATION
In the open position, the valve is full bore with no flow restrictions. During closing, two pinch bars squeeze the valve sleeve shut on the centerline. Bubble tight shut-off is provided even if solids have built up on the sleeve wall. The rubber sleeve is the only wearing part which significantly reduces maintenance costs and extends service
intervals.
Pinch valves can be either shut off valves (also known as isolation valves) or control valves, and provide superior performance in the most demanding applications, where conventional valves encounter problems with wear due to increased turbulence. When the controlled flow is abrasive, it is a big advantage to have only one, wear resistant, valve part in contact with the medium. Because of this, the need for maintenance and spare parts is greatly reduced.
As the valves are self-cleaning, even if any solids are accumulated in the sleeve wall, it breaks away when the valve is operated. This is due to the flexibility of the sleeve, making the valve lifetime longer than many other competing products on the market. The sleeve is naturally wear resistant and when particles hit the sleeve’s rubber surface, the energy is absorbed and released when the rubber bounces back.
Strongly consider the use of a pinch valve to retrofit or replace the failing ball, butterfly, or gate valve in your application. Most plant maintenance and engineering staff will tell you they are very pleased with the decision.
For more information on the many uses and applications of pinch valves, contact Automatic Controls of Virginia. They can be reached by calling (804) 752-1000 or visit their web site at https://acva.com.
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The Val-MaticQuadrosphere forged ball valve is a proven unique trunnion mounted ball valve design for long life in numerous industrial applications where fluids with sediment tends to clog and damage traditional ball valves. The ball is not spherical, as in a typical ball valve. Surfaces of the ball are contoured with recessed surfaces on four sides of the ball. The contoured recess surfaces provide for extra flow paths and also provide lift edges that wipe the body seat clean during opening and closing. The hard chrome plated stainless steel ball provides low friction and abrasion resistance. The recessed surfaces provide multiple flow paths for particulates to be flushed from the body during every operation, thereby providing a self-cleaning valve.
The valve is equipped with a seat on both ends to provide bi-directional seating. The seating is available in double block and bleed (DBB) or double isolation and bleed (DIB) depending on the application. As with all trunnion mounted ball valves, when line pressure is applied to the valve, fluid flows behind the seat ring and presses the seat ring and resilient seal insert against the ball to make a tight seal. The ball is directly anchored to the body by rigid trunnions. The ball will rotate 90 degrees during opening and closing but the trunnions prevent any axial motion of the ball during pressurization. The valve stem is equipped with a shoulder to prevent blowout during process operations. The stem is sealed with o-rings and graphite packing for low fugitive emissions and fire safe applications. An emergency injection fitting is provided for emergency sealing until maintenance can be performed.
For applications like geothermal fluid where scale and sediment are present in high concentrations, the optional ring master seat is used. The ring master uses an external pressure source such as grease or gas to press the seat to insert against the ball. Since the injection pressure is greater than the line pressure, the seat ring pocket is always isolated from the process fluid and cannot collect sediment over time. One method of applying external pressure to the seat is with a pressurized accumulator assembly. Grease or other compatible fluid is injected into the valve and the assembly until the seating pressures slightly higher than the process pressure is achieved. The pre-charged accumulator maintains the proper seating pressure over time.
The Quadrosphere is available in sizes 2 to 24 inches and ansi pressure classes to 2500. The valves are manufactured in accordance with industry ball valve standards API 6d and 608. The valves have also been certified to fire safe and fugitive emissions standards.
The presence of air in a pipeline and its impact on operations is probably one of the most misunderstood phenomena in our industry today. Many operational problems are blamed on inadequate thrust blocking, improper pipeline bedding, etc. These problems include broken pumps, valves and pipe, as well as faulty instrumentation readings. In reality, many of these problems are not caused by improper installation of the equipment but by failure to de-aerate the pipeline. It has been said that if a pipeline is properly de-aerated, you can't guarantee against a line break. However, if you don't properly de-aerate a pipeline, you should be prepared for one.
