Showing posts with label flow control. Show all posts
Showing posts with label flow control. Show all posts

Flow & Pressure Instrumentation for Biopharmaceuticals & Life Sciences

Flow & Pressure Instrumentation for Biopharmaceuticals & Life SciencesProducing biopharmaceuticals is one of the world’s most demanding manufacturing processes.

Brooks Instrument’s mass flow and pressure control technology helps maximize cell culture yields and control bioprocess costs. Their flow
and pressure controllers set global standards for reliability, repeatability and long-term stability.

Brooks Instrument mass flow controllers (MFCs) satisfy key biotechnology research and production requirements:
  • Tight control of DO and pH during experiments and production
  • NO unplanned downtime due to high cost of losing a batch or experiment
  • Ability to rapidly diagnose and resolve issues with bioreactors or fermentation equipment
  • Cost-effective method for adhering to regulatory requirements
  • Excellent technical support and rapid response for equipment service


Cavitation - Scourge of Industrial Process Control Valves Everywhere

Cavitation produces vapor bubbles in liquids
Cavitation produces bubbles in flowing process liquids
Consider a generic industrial fluid process control operation. There are pumps, valves, and other components installed in the process lines that, due to their interior shape or their function, cause changes in the fluid motion. Let's look specifically at control valves and how their throttling operation can create conditions able to greatly impact the valve itself, as well as the overall process.

Fluid traversing a control valve can undergo an increase in velocity when passing the constriction presented by the valve trim. Exiting the trim, fluid then enters the widening area of the valve body immediately downstream with a decrease in velocity. This change in velocity corresponds to a change in the kinetic energy of the fluid molecules. In order that energy be conserved in a moving fluid stream, any increase in kinetic energy due to increased velocity will be accompanied by a complementary decrease in potential energy, usually in the form of fluid pressure. This means the fluid pressure will fall at the point of maximum constriction in the valve (the vena contracta, at the point where the trim throttles the flow) and rise again (or recover) downstream of the trim.

This is where cavitation begins.

If the fluid being throttled is a liquid, and the pressure at the vena contracta is less than the vapor pressure of the liquid at the flowing temperature, portions of the liquid will spontaneously vaporize. This is the phenomenon of flashing. If, subsequently, the pressure of the fluid recovers to a level greater than the vapor pressure of the liquid, any flashed vapor will rapidly condense, returning to liquid. This collapse of entrained vapor is called cavitation.

Flashing, the generation of vapor bubbles within the liquid, will precede and set the stage for cavitation. When the flashed vapor bubbles condense to liquid they often do so asymmetrically, with one side of the bubble collapsing before the rest of the bubble. This has the effect of translating the kinetic energy of the bubble’s collapse into a high-speed “jet” of liquid in the direction of the asymmetrical collapse. These liquid “microjets” have been experimentally measured at speeds up to 100 meters per second (over 320 feet per second). What is more, the pressure applied to the surface of control valve components in the path of these microjets can be intense. An individual microjet can impact the valve interior surfaces in a very focused manner, delivering a theoretical pressure pulse of up to 1500 newtons per square millimeter (1.5 giga-pascals, or about 220000 PSI) in water. In an operating fluid system, this process can be continuous, and is known to be a significant cause of erosive wear on metallic surfaces in process piping, valves, pumps and instruments. As the rapid change in pressure takes place, the bubbles (voids in the liquid) collapse (implode), and the surrounding metal surfaces are repeatedly stressed by these implosions and their subsequent shock waves.

Consequences for control valves, as well as for the entire control process, vary and are often destructive. They may include:
  • Loud noise
  • Strong vibrations in the affected sections of the fluid system
  • Choked flow caused by vapor formation
  • Change of fluid properties
  • Erosion of valve components
  • Premature destruction or failure of the control valve 
  • Plant shutdown
The video provides a visual demonstration, through clear piping, of what happens inside the piping system when a valve is operated in a manner that causes substantial cavitation.

The solution lies in minimizing the potential for cavitation to occur through proper valve selection and sizing, along with coordinating operating characteristics of pressure drop inducing components with the total system performance. One valve manufacturer's recommendations are summed up in four basic approaches.
  • Avoidance of cavitation through proper valve selection. Use a valve with a rated liquid pressure recovery factor greater than that required for the application. Some applications may be suitable for the use of an orifice plate downstream of the valve.
  • Cavitation Tolerant Components capable of withstanding limited amounts of cavitation without excessive wear. Increased flow noise is likely to accompany this route.
  • Prevention of cavitation through the use of valve trim design that reduces pressure in several steps, avoiding excessive flashing. These valves can be expensive, but their effectiveness makes them an alternative worth considering.
  • Containment of the harmful effects of limited to moderate cavitation through trim designs that eliminate contact of the fluid with metal surfaces which are more susceptible to damage.
Share your requirements and application challenges with a valve specialist and gain insight through their recommendations. Combining your process knowledge with their product application expertise will yield a great solution.


Thermal Mass Flow Controller - Product Enhancement

Brooks Instrument SLA 5800 Thermal Mass Flow Meter
Newly Enhanced Thermal Mass Flow Meters
And Electronic Pressure Controllers
Courtesy Brooks Instrument
Brooks Instrument, world recognized leader in thermal mass flow controllers and mass flow meters, has improved upon its premier family of smart digital thermal mass flow controllers and meters. The newly enhanced SLA Series features:

Enhanced temperature stability
Upgraded electronics
Improved accuracy
Zero-drift diagnostics
High turndown ratio

Multiple communication protocol support, and more.

The video included below will show you all the latest improvements on this product line that has thousands of units in its installed base throughout many industries and applications.

Application assistance and detailed information is available from product specialists. Combine their product and application knowledge with your own process expertise to generate a positive outcome.

Know Your Control Valve Basics?

Industrial Control Valve Cutaway View
Courtesy Cashco
Understanding basic operation and function of control valves, an integral part of many industrial process control loops, is essential for the process engineer, operator, or other stakeholder. This presentation outlines control valve operation, major components, and terminology used to describe valve parts, functions, and principles of operation. A useful reference for stakeholders in need of a refresher course in order to understand what the engineers are saying, it also provides detailed illustrations, charts, and description that will prove valuable to the more technical minded.


What you will find:


  • Terminology: A glossary of terms commonly used in the control valve world.
  • Control Valve Basic Designs: Control valve classifications, cutaway illustrations showing the operating structure of different valve types, comparisons of varying valve designs.
  • Characterization and Trim Design: Flow characteristic curves and comparisons for different valve types, showing how flow responds to valve position change.
  • Control Valve Technical Considerations: FTC vs FTO, illustrations showing valve operation.
  • Force-Balance Principle: Illustration and formula explanations of this basic operating principle.
  • Actuator Basic Designs: Illustrations showing the differing arrangements for actuator operation.
  • Control Valve Unit Action: Illustrations, diagrams, and explanations of a range of valve operating conditions, including loss of electrical power and loss of instrument air supply.
  • Actuator Benchset Range: Shows practical relationship between instrument air pressure and valve ability to properly operate at various pressure conditions.
  • Valve Positioner Basics: Definition of valve positioning, reasons to use a positioner, schematic illustrations of control loops.
  • Control Loop Action: Charts and provides examples of 16 combinations of Process, Controller, Positioner, and Control Valve combinations.
  • Control Valve Packing Designs: Describes and defines packing, common problems, current state of the art. Cutaway illustrations of various packing arrangements.
  • Seat Leakage: Classifications, comparisons of different materials.


There is something of value in the document for everyone, and you will undoubtedly pick up something useful. Thanks go out to the engineers at Cashco for putting this together. You can discuss any aspect of your control valve applications with a product specialist. Your contact is always welcome.




Valve Selection: A Look at Ball Valves

industrial ball valves
Industrial Application Ball Valves
In the realm of industrial process control valves, your selections for most applications are vast. Every application will likely have one or more elements become critical and deciding factors for valve selection. That element might be complex and highly technical, being intimately related to physical or dynamic properties few understand. Conversely, the selection may hinge upon something as obvious as what will fit in the space that is provided. Whatever the case, some efficiency can be brought to bear in your selection process by initially deciding which type of valve would best suit the application. This allows you to focus on a much smaller universe of product candidates for your project.

Like most valves, ball valves are characterized by their closure mechanism.  Generally, a ball valve has a spherically shaped fabrication (ball) that is inserted in the fluid flow path. The ball has an opening through its center, often circular in cross section and matching the diameter and shape of the connected pipe. The ball is contained within the body of the valve and rotated around its central axis by torque applied to the stem. The stem, which extends through a seal to the exterior of the valve body, can be manually or automatically controlled via several methods.

During valve operation, the ball is rotated through a ninety degree arc from a fully closed to fully open position. When fully closed, the opening in the ball faces the sidewalls of the valve body and is cut off from the fluid by seals that secure the ball in place and prevent fluid flow around the ball. As the valve stem is rotated toward the open position, the cross sectional area of the opening is increasingly exposed to the fluid flow path until the open area through the ball is aligned with the flow path in the fully open position.

Consider some of these main points and see if a ball valve might be a good selection for your application.

In the plus column:
ball valve in gas pipeline
Large Ball Valve in a Gas Pipeline
  • When closed this valve type provides a tight closure. When open fully,there is very low resistance to flow.
  • Suitable for applications requiring only fully closed or open control.
  • With only 90 degrees of rotational motion from open to closed positions, ball valves can provide rapid response to a change in position requirement or command.
  • Ball valves are comparatively compact, without the space requirement for extending stem movement as required by some other valve types.
  • Ball valves are available in a wide range of construction materials for the body, stem, ball, and seals, making them suitable for a wide range of fluid types and temperatures.
  • Force required to rotate to valve stem is moderate, keeping actuator options high and energy requirements low.
  • A full size port provides for very low pressure drop across the valve when fully open.
  • Requirements for maintenance are generally low. No lubrication required.

In the other column:
  • Ball valves are not well suited for throttling applications. Partially open valves expose the seals to the effects of the flow velocity, with possible premature seal deterioration.
  • A closed valve can trap residual amounts of fluid in the port (the opening through the ball). This fluid will be released to the valve outlet when the valve is opened.
  • Elastomeric materials are often used for the valve seals. Evaluate whether the seal materials are compatible with the fluid characteristics and operating temperature.

There are special adaptations of ball valves which may overcome some of the concerns you have about their application on your project. It is always a good idea to consult with a valve specialist and consider their recommendations for your project.

Gate Valve: A Good Choice for Your Application?

Automatically operated gate valve
Gate Valve With Actuator
Courtesy Orbinox
Fluid flow control is an essential component of many industrial applications. Because of its prevalence, and the variety of applications, there are many types, sizes, and arrangements of flow control valves available to meet practically any need. The challenge for the specifying engineer is to select the valve type and arrangement that will provide the needed performance, while also fulfilling the need for safe performance and a desire for low maintenance burden. Sorting through the wide array of valves and targeting the correct valve technology or type can quickly narrow your focus to a much smaller circle of products to research and consider.

Industrial gate valves, like all other valves, regulate fluid flow by reducing or expanding the area through which the process fluid must pass in a closed system. It is the manner in which that restricting area is changed that serves the major discriminating factor among the different valve types. In the case of a gate valve, a sliding round or rectangular piece, known as the gate or disc, is moved by a mechanism and transects the fluid flow path. Closing the gate, completely transecting the flow path, will restrict the flow to its fullest. As the gate is retracted and the opening size increases, flow is increasingly enabled. The movement of the gate, along with valve body and mechanism construction, give this valve type an array of positive and negative attributes.

High Marks for Gate Valves:

  • Low resistance to fluid flow when the valve is completely open. Generally, the cross sectional characteristics of a gate valve will mimic those of the connected piping system. Additionally, gate valves do not impose any change in the flow direction of the fluid as it passes through the valve body.
  • Low force and energy requirements are needed to change the valve opening position (the position of the gate). Since gate movement is perpendicular to the direction of flow, it is not necessary for the mechanism to counteract the full pressure drop of the fluid in the system.
  • Gate valves can be bi-directional, controlling flow in systems that may incorporate a reversal of the flow direction.
  • The installed gate valve is shorter in length than most other designs.
  • Gate valves employ a slow closure rate. The accompanying slow reduction in fluid shutoff can inhibit physical shock (hammering) in the connected piping system.

manually operated gate valve
Manually Operated Gate Valve
Courtesy Orbinox
Things that appear as positives in favor of gate valve selection on one application may not be as desirable on another.

Gate Valve Potential Negatives:

  • Valve seals are exposed to the fluid flow when the valve is open. This might make the seals vulnerable to the wearing effects of entrained foreign matter or other components of the process fluid. The end result could potentially be prematurely worn sealing surfaces and a failure of the valve to seal properly.
  • Gate valves are generally slow to open and close. This attribute might make them a poor selection for an application requiring rapid or immediate action.
  • The gate valve will require an extended overhead service area, compared to other valve types. This may have an undesirable impact on locating the valve where desired.
  • Fluid flow control applications that require throttling of the flow are generally not good candidates for a gate valve. Fluid flow through a partially open gate valve may cause the closure mechanism to vibrate. Additionally, there are concerns associated with potential erosion of the gate and seals due to increasing fluid velocities when the valve is partially open

These, and other, very basic considerations may help point your product search in the right direction. One additional recommendation is that you contact an experienced valve specialist and take advantage of their knowledge and experience fulfilling other applications similar to yours.