Valve Selection: A Look at 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:

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.

Valve Selection - When to Choose a Butterfly Valve

Industrial process control valves are available in a staggering array of materials, types, and configurations. An initial step of the selection procedure for a valve application should be choosing the valve type, thus narrowing the selection field to a more manageable level. Valve "types" are generally defined by the closing mechanism of the valve.

Butterfly Valve
Courtesy Crane CPE

A butterfly valve has a disc that is positioned in the fluid flow path. It rotates around a central axis, the stem, through a 90 degree arc from a position parallel to the flow direction (open) to perpendicular (closed). A variety of materials are used in the valve body construction, and it is common to line the valve with another material to provide special properties related to the process media.

What might make a butterfly valve a beneficial selection over another valve type?

• The closure arrangement allows for a comparatively small size and weight. This can reduce the cost, space, and support requirements for the valve assembly.
• Generally low torque requirements for valve operation allow for manual operation, or automation with an array of electric, pneumatic, or hydraulic actuators.
• Low pressure drop associated with the closure mechanism. The disc in the flow path is generally thin. In the fully open position, the disc presents its narrow edge to the direction of flow.
• Quarter turn operation allows for fast valve operation from fully closed to fully open.
• Some throttling capability is provided at partially open positions.
• Small parts count, low maintenance requirements.

What may be some reasons to consider other valve types?

Butterfly Valve
Courtesy Crane CPE

• Butterfly valve throttling capability is generally limited to low pressure drop applications
• Cavitation can be a concern.
• Some sources mention the possibility of choked flow as a concern under certain conditions.

Butterfly valves, like other valve types, have applications where they outperform. Careful consideration and consultation with a valve expert is a first step toward making a good selection.

Gate Valve: A Good Choice for Your Application?

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
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.

Process Measurement and Control Essentials – Industrial Pressure Transmitters

Industrial Liquid Level
Transmitter
Courtesy Yokogawa Corp.

The measurement and control of fluid pressure is ubiquitous throughout many industrial processes. Measurements of pressure, directly and indirectly, provide real time information about what is happening in places that cannot be seen, such as inside a pipe, tank, or machine. The very nature of “process” suggests movement and change, the control of which is necessary to produce a consistent desirable outcome. Industrial pressure transmitters employ specific technologies and physical principals to derive a measurement of process pressure, then deliver or transmit, the measured value to a controller or recording device.

Fluid pressure tells a process operator much about what is currently happening. The pressure variable can be used to determine, among many industrial process elements:

• Degree to which the process is conforming to a recipe or specification
• Whether machinery is performing within its specified operation range
• If conditions of the process remain within the bounds established for safety
• A quantity measurement of flow, mass, or volume

Differential Pressure
Transmitter
Courtesy Yokogawa Corp.

Global industrial processes have widely varying physical arrangements, operating environments, and measurement requirements. Manufacturers of industrial pressure transmitters have responded with an immense array of transmitter technologies, arrangements, and configurations. When selecting the best suited pressure transmitter for your application, consult a sales engineer and consider some of the following:

• Signal requirements – Type, distance, possible sources of interference
• Device environment – Hazards, extreme conditions of temperature or corrosion
• Accuracy and stability of measurement
• Response time to changes in the process condition
• Ratings and certifications required for the device
• Configuration, arrangement, and mounting aspects of the transmitter device

Explore the differing technologies and how they can be best applied to implement or improve your process. Experienced sales engineers can be a useful sounding board for discussing your needs. Take advantage of their extensive experience with a wide array of process applications.

Process Measurement and Control - Selecting the Right Flow Meter Technology

Vortex Flow Meter
Courtesy Yokogawa Corp.

Magnetic Flow Meter
Courtesy Yokogawa Corp.

Many industrial process control operations require fluid flow measurement as an essential element in the process design. Accurate flow measurement can be obtained with the proper application and installation of a flow meter as part of the fluid transfer system.

Industrial flow meters employ differing technologies to directly or indirectly measure fluid flow rates. Among the many available technologies for fluid flow measurement, vortex flow meters, magnetic flow meters, Coriolis flow meters, and rotameter flow meters are among some of the most common found in industry.

Coriolis Flow Meter
Courtesy Yokogawa Corp.

Rotameter Flow Meters
Courtesy Yokogawa Corp.

Each of the separate technologies have attributes which can make them more suitable to certain applications. Selecting the most appropriate flow measurement technology for an application is one of the initial and crucial steps to designing a well functioning fluid measurement system.

Selection criteria, such as fluid temperature, pressure, and velocity will be part of the selection process. Additional considerations include whether the fluid may be abrasive, corrosive, clean or dirty. The state of the fluid, liquid or gas, must also be considered.

The table below provides quick general guidance on which technologies to consider, based upon the factors outlined above. This will help you better focus further product selection research efforts.

Flow Meter Technology Selection Table
Courtesy Yokogawa Corporation of America

Selecting the right valve is not always an easy task, especially since it may be something that you do infrequently. Manufacturers often have knowledgeable local representatives that are experienced in this field and more than willing to contribute their expertise to your selection process.

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