Control Valve Cavitation Solutions

Cavitation is the formation of vapor spaces (bubbles) in the control valve cavity resulting from a rapid change in pressure. When the bubbles move downstream and are exposed to a larger cross-sectional area, velocity decreases and pressure increases, the surrounding higher pressure causes the lower pressure bubble to implode, which causes shockwaves. These shockwaves can cause metal fatigue and cause excessive wear on the internals of the valve. As the bubbles collapse, they make a discernible sound with accompanying vibration, and the damage to a valve can happen quickly (weeks or months).

Cavitation is very destructive and may wear out the trim and body parts of the valve in a short time. Using hard internal materials provides a slight improvement but costs more.

Flowserve Valtek Cavitation Solution Control Valves prevent cavitation damage and minimize hydrodynamic noise even under the most severe liquid applications. Their unique, patented designs eliminate cavitation damage and provide straightforward maintenance and a long life even with demanding applications. 

For more information about Flowserve Valtek Control Valves in Florida, contact Instrument Specialties by calling +1 407.324.7800  or visiting https://isisales.com.

The Flowserve Valtek Compressor Anti-Surge Valve

The Flowserve Valtek Compressor Anti-Surge Valve is a groundbreaking approach to anti-surge control by combining accurate control with exceptional responsiveness in a simple, reliable package. It is designed to address common challenges seen in compressor applications, where the surge of compressors can cause equipment failure and downtime. 

By providing rapid response, driving the valve open when required, and providing steady-state positioning when recycling, the Valtek Compressor Anti-Surge Valve solution protects the compressor from catastrophic surge damage. The Valtek Compressor Anti-Surge Valve also provides the benefits of fast and simple set-up as well as easy maintenance. In addition, to existing installations, the Logix 3800JF positioner is easily retrofitted.

For more infomration about Flowserve Valtek products in Florida, contact Instrument Specialties. Call them at 407-324-7800 or visit their website at https://isisales.com.

The Flowserve Valtek FlowTop GS General Service Control Valve

The Valtek FlowTop GS control valve (types V746 and V748) improves the reliability and uptime of production processes while minimizing operating and maintenance costs. Designed for general service applications, the FlowTop GS globe valve is a competitively priced, fully integrated valve-actuator-instrumentation package for continuous process flow loop control throughout the plant.

For more information, and to download a PDF cutsheet, visit this Instrument Specialties webpage.

Kammer Brand Valves Targeted at Special Applications

Control valve for severe service and high pressure drop.
Image courtesy Flowserve - Kammer

Kammer, a brand of the Flowserve Corporation, manufactures automatic control valves, with a focus on special applications. Specific products of the company are targeted at fluid control operation in applications with:

• Low temperatures, extending to cryogenic.
• High pressure, up to 60,000 psi.
• Corrosive media
• Low and micro flow
• Sanitary and aseptic requirements
• Severe service

Kammer also manufactures actuators for automating valve operation. The brochure provided below provides an overview of the Kammer product line of linear control valves for targeted applications. Share your fluid control requirements and challenges with a valve specialist and develop an effective solution by leveraging your own knowledge and experience with their product application expertise.

Kammer Valve Product Overview - Control Valves from Instrument Specialties, Inc.

Eight Selection Criteria for Control Valves

Control valve shown with actuator and positioner
Image courtesy Flowserve - Valtek

Proper selection with respect to a number of factors plays an important role in obtaining the desired performance from a control valve. Failure to make a properly considered selection can impact operation, productivity and safety. Here is a quick checklist of basics that need to be considered:

• Control valves are not intended to be a an isolation valve and should not be used for isolating a process. 
• Always carefully select the correct materials of construction. Take into consideration the parts of the valve that comes in to contact with the process media such as the valve body, the seat and any other wetted parts. Consider the valve's exposure to operating pressures and temperatures. Finally, also consider the ambient atmosphere and any corrosives that can occur and effect the exterior of the valve. 
• Put your flow sensor upstream of the control valve. Locating the flow sensor downstream of the control valve exposes it to an unstable flow stream which is caused by turbulent flow in the valve cavity.
• Factor in the degree of control you need and make sure your valve is mechanically capable. Too much dead-band leads to hunting and poor control. Dead-band is roughly defined as the amount of control signal required to affect a change in valve position. It is caused by worn, or loosely fitted mechanical linkages, or as a function of the controller setting. It can also be effected by the tolerances from mechanical sensors, friction inherent in the the valve stems and seats, or from an undersized actuator. 
• Consider stiction. The tendency for valves that have had very limited travel, or that haven't moved at all, to "stick" is referred to as stiction. It typically is caused by the valves packing glands, seats or the pressure exerted against the disk. To overcome stiction, additional force needs to be applied by the actuator, which can lead to overshoot and poor control.
• Tune your loop controller properly. A poorly tuned controller causes overshoot, undershoot and hunting. Make sure your proportional, integral, and derivative values are set). This is quite easy today using controllers with advanced, precise auto-tuning features that replaced the old fashioned trial and error loop tuning method.
• Don't over-size your control valve. Control valves are frequently sized larger than needed for the flow loop they control. If the control valve is too large, only a small percentage of travel is used (because a small change in valve position has a large effect on flow), which in turn makes the valve hunt. This causes excessive wear. Try to always size a control valve at about 70%-90% of travel.
• Think about the type of control valve you are using and its inherent flow characteristic. Different types of valve, and their disks, have very different flow characteristics (or profiles). The flow characteristic can be generally thought of as the change in rate of flow in relationship to a change in valve position. Globe control valves have linear characteristics which are preferred, while butterfly and gate valves have very non-linear flow characteristics, which can cause control problems. In order to create a linear flow characteristic through a non-linear control valve, manufacturers add specially designed disks or flow orifices which create a desired flow profile.

These are just a few of the more significant criteria to consider when electing a control valve. You should always discuss your application with an experienced application expert before making your final selection.

Flowserve ValveSight Diagnostic Solution for Control Valves

The video shared this week, from Flowserve, provides an overview of their ValveSight real time online diagnostic solution for use with control valves and associated actuators, positioners and controls. ValveSight enables operators to keep valves in service longer by detecting potential failures before they occur. The system provides a deep level of monitoring and diagnostic functions which are described in the video. Reducing unplanned downtime is a common goal among all facilities and plant operators. Check out the short video, and share your questions about the system with an application specialist.

Video of Valtek Packing Subassembly

The Mark One, from the Flowserve brand Valtek, is a globe valve intended for flow control of liquids or gases across a wide range of applications. The valve design provides high positioning accuracy, repeatability and tight shutoff. A wealth of special design and construction features make the Mark One a serious contender for almost any fluid control operation.

Share your control valve and valve automation requirements and challenges with an application specialist, combining your own process knowledge and experience with their product application expertise to develop an effective solution.

Eccentric Rotary Plug Control Valve

The MaxFlo 4 eccentric rotary plug control valve
Image courtesy of Flowserve Valtek

There is a seemingly limitless array of industrial control valves, each targeted for a range of fluid applications and fortified with materials and design features specifically suited for meeting the challenges of that application range.

Flowserve, under their Valtek brand, developed a control valve that combines a number of useful design features. The MaxFlo 4 is an eccentric rotary plug valve intended for fluid control operations. The valve has some attractive design features.

• There is no shaft extending through the flow path, leaving flow unobstructed when the valve is fully open (see the illustration in the document included below).
• Valve trim provides tight bi-directional shutoff.
• Metal or soft seat construction is available to accommodate a wide range of applications.
• A variant provides flange to flange dimensions that allow the MaxFlo 4 to drop in as a replacement for standard size globe valves.
• High Cv rating may enable use of a smaller valve, when compared to other designs.
• Precise position control is delivered by the shaft form and plug mounting.
• Double offset eccentric plug eliminates sliding of plug across sealing surfaces, reducing wear and required seal maintenance.

More detailed information is provided in the document provided below. There is a revealing cutaway illustration showing the mounting and movement path of the plug. Share your industrial process control valve requirements and challenges with an application specialist to get the best match of control valve to application.

Eccentric Rotary Plug Industrial Control Valve from Instrument Specialties, Inc.

Control Valve Flow Characteristics

Industrial Control Valve
Courtesy Flowserve - Valtek

Flow characteristics, the relationship between flow coefficient and valve stroke, has been a subject of considerable debate. Many valve types, such as butterfly, eccentric disk and ball valves, have an inherent characteristic which cannot be changed (except with characterizable positioner cams). Flow characteristics of globe valves can be determined by the shape of the plug head.

The three most common types of flow characteristics are quick opening, equal percentage and linear. The adjacent figure shows the ideal characteristic curve for each. These characteristics can be approximated by contouring the plug. However, inasmuch as there are body effects and other uncontrollable factors, plus the need for maximizing the flow capacity for a particular valve, the real curves often deviate considerably from these ideals. When a constant pressure drop is maintained across the valve, the characteristic of the valve alone controls the flow; this characteristic is referred to as the “inherent flow characteristic.” “Installed characteristics” include both the valve and pipeline effects. The difference can best be understood by examining an entire system.

Control valve flow properties
Courtesy Flowserve - Valtek

Equal Percentage

Equal percentage is the characteristic most commonly used in process control. The change in flow per unit of valve stroke is directly proportional to the flow occurring just before the change is made. While the flow characteristic of the valve itself may be equal percentage, most control loops will produce an installed characteristic approaching linear when the overall system pressure drop is large relative to that across the valve.

Linear

An inherently linear characteristic produces equal changes in flow per unit of valve stroke regardless of plug position. Linear plugs are used on those systems where the valve pressure drop is a major portion of the total system pressure drop.

Quick Open

Quick open plugs are used for on-off applications designed to produce maximum flow quickly.

This information provided courtesy of Flowserve Valtek. Share your control valve requirements and challenges with a valve specialist, combining your own process knowledge and experience with their product application expertise to develop effective solutions.

Application of Rugged Dump Valve and Liquid Level Control on Separator

Model 1450 Valve
Courtesy SOR

SOR, a globally recognized manufacturer of measurement and control equipment and instruments, recently published an application note about the use of two of their products in combination.

The SOR® 1600 Series level controllers are designed for liquid level and interface control applications calling for either modified percent (throttling) or quick opening (snap) pneumatic service. The device is fully mechanical and provides a pneumatic output signal.

SOR's Model 1450 valve is a close-coupled control valve designed to meet pressure and erosive applications common to the oil and gas industry. The intended applications for the valves include controlling liquid level on 2 or 3 phase gas separators, gas dehydrators, compressors, scrubbers, heat treaters, well test systems, and other oil field equipment. Ease of maintenance, rugged steel construction, hardened trim, application flexibility, and a range of safety features are all designed into the product.

The application note illustrates how these two products provide control of a separator. Whatever your fluid process control application, share your challenges with process control specialists, combining your process knowledge with their product application expertise to develop effective solutions.

Separator Control with liquid level control and dump valve from Instrument Specialties, Inc.

The Valtek Control Valve: Understanding the Components

Flowserve (Valtek) control valves

Valtek control valves are also known for handling the most severe services: cryogenic, superheated steam, volatile and corrosive fluids, erosion, high pressure drops, vibration, cavitation, flashing, and high noise levels.

Valtek valves are equipped with spring cylinder or spring diaphragm actuators that provide the thrust and speed necessary to manage any service. Valtek four-way analog and digital positioners provide accuracy and response to handle the most exacting applications.

This video gives the viewer an understanding of the major components.

For more information, contact:
Instrument Specialties Inc.
3885 St. Johns Parkway
Sanford, FL 32771
phone 407.324.7800
fax 407.324.1104
e-mail: offices@isisales.com

Design and Construction of the Globe Control Valve (Valtek Mark One)

Globe control valve

A globe control valve is a specific type of valve used for regulating flow in a pipe. The design includes a movable plug, connected to a stem, which can be moved linearly to close or open the valve. Globe control valves are referred to as “linear” valves because of this movement, whereas ball valves and butterfly valves are referred to as “quarter-turn” valves. Generally, globe control valves provide better overall flow control than quarter-turn valves due to the design of their flow path.

The Valtek Mark One globe control valve is know for superior performance in liquid and gaseous services, while also permitting easy, fast and inexpensive maintenance to its major components.

The video below provides an excellent look inside a globe control valve (in this case the Flowserve Valtek Mark One).

On the Bench. A Look Inside the Valtek Mark One Globe Control Valve

Glove Control Valve

The video below provides the viewer with a look inside the Valtek Mark One control valve and identifies its major components.

The Valtek® Mark One globe control valve is designed for liquid and gaseous services, and for permitting easy, fast and inexpensive maintenance.

The spring-cylinder actuated Mark One valve provides stiffness and maintains high positioning accuracy, repeatability, controlled high speed, and faithful response. The Mark One valve handles up to 150 psig supply air and has the thrust to shut off against much higher fluid pressures.

The Mark One valve is designed so the spring, supply air pressure and fluid pressure itself combine to produce exceptionally tight shutoff. A self-aligning seat ring further enhances the shutoff capability of the valve.

Basic Lesson on Flow Control Valves

For anyone interested in flow control basics, control valve basics, check valve basics and many other technical topics, videos are available on YouTube from the Columbia Gorge Community College. The teacher's name is Jim Pytel and he does an excellent job. Here's a video tutorial Flow Control Valve basics.