Friday, June 26, 2015

Selecting The Right Valve Type - Ball Valves

Applications that can be characterized as industrial fluid handling or process control are vast in number and variety, each being highly specialized and customized to specific circumstances. It’s no surprise that, given the array of potential application conditions, there are countless different valve arrangements, types, and technologies to choose from.
Industrial Ball Valve
Large Industrial Ball Valve
Courtesy HS Valve Co.
Ball valves, like many valve types, are named for their closure mechanism. A spherical shaped element is placed in the fluid flow path, with the ability to rotate its position around an axis. The axis is a shaft or other device that connects to an actuator on the exterior of the valve and flow path. The actuator can be a simple handle or an element of a valve automation system. The “ball” in the ball valve has an opening through its center, usually round to mimic the shape of the connected pipe. As the ball is rotated, the opening aligns with the inlet an outlet of the valve body, allowing fluid to pass. A counter-rotation that aligns the opening with the sides of the valve body, away from the flow path, stops the fluid flow. So, compared with other valve technologies, when would a ball valve be a preferred application choice? Here are some points to consider.

Application advantages of ball valves:

  • Leak-proof service
  • Well suited for processes requiring only full flow or no flow operation.
  • Rapid open and close action, requiring only 90 degrees of rotation from fully open to fully closed.
  • Comparatively light weight and small size.
  • Wide range of construction material options for body, ball, and seals make them suitable for many applications.
  • Require only moderate force to control valve position.
  • Flow path opening in the ball will often be “full port”, providing same cross section as the connected pipe and adding very little restriction or pressure drop to the flow.
  • Low maintenance, with no lubrication required.

What considerations might be cause to consider a different valve type?

  • There can be some residual fluid trapped in the valve when it closes.The trapped fluid will be released when the valve is opened. Consider what impact, if any, this may have on your process.
  • Balls valves are generally not suited for throttling applications. When partially open, the seals that surround the ball are exposed to the flow velocity and can deteriorate quickly.
  • Valve seals are usually elastomeric materials. Verify seal materials are compatible with the fluid type, character and operating temperature.

These comments are general in nature and there are some specialized ball valve designs that have overcome some of the general disadvantages noted here. Have a conversation with a valve specialist about your application and benefit from their experience and knowledge.

Monday, June 22, 2015

Selecting the Right Valve Type - Gate Valves

There are many types of valves available for industrial fluid handling and process control applications. Specifying the proper valve type for an application can be made easier with some basic knowledge about the application strengths and weaknesses of the various valve types.

gate valve cutaway view
Gate Valve Cutaway View
Courtesy DHV Industries
Gate valves open and close by changing the position of a rectangular or round wedge (the gate) in the fluid flow path. The sealing surfaces are arranged in a planar fashion and the gate, which is commonly either flat or wedge shaped, slides along the sealing surface from the open to closed position. Because of the cross-sectional shape of pipes, which is often mimicked in the valve body, the size of the opening created as the gate valve opens and closes does not change at the same rate as the percentage of total available movement of the gate. This non-linear aspect of valve operation can make a gate valve less suitable for an application where flow rate must be accurately controlled across the range from fully open to fully closed. Complicating throttling operations further is the possibility of the gate vibrating when partially open, due to the fluid flow around the gate assembly. Unless specifically designed for throttling, gate valves are generally best suited for applications requiring either full flow or no flow. Because of its operating nature and construction, a gate valve may prove to be the appropriate selection, based upon the type of media or fluid which is being controlled.

In addition to specifying the manner in which the valve will be connected within the piping system, consideration should be given to construction of the valve body. If it may be necessary to inspect, service, or clean the valve interior, look for a bonnet connection that will permit suitable access to the valve interior.

Once you have decided that a gate valve will be the most suitable type for your application, there are many other considerations in valve selection. Draw on the experience and knowledge of coworkers, maintenance technicians, and valve sales engineers to help specify a valve assembly that meets the needs of all project stakeholders.

Friday, June 19, 2015

Industrial Control Valve Basics - An Introduction

Industrial process control valve
Globe Valve with Pneumatic Actuator
Courtesy Warren Controls
Valves, mechanical devices able to control flow or pressure in a process or system, are as ubiquitous as any industrial process control element. As essential components of piping systems conveying liquid, gas, vapor, or slurry, valves are a component with which almost every industrial process and control engineer will require more than entry level familiarity. They are the controlling element in almost any fluid handling system. What are some of the very basic knowledge points for specifying and selecting a control valve?

There are numerous types of valves available, including butterfly, ball, check, globe, gate, diaphragm, plug, and control valves as the most common. Particular valve types can be better suited to the medium being controlled, or have functional capabilities making them a better selection for your process application. Within each type there will be a wide range of options and features that allow for close tailoring of the complete valve assembly to match the application requirements.  Some valves can be self-operated, while others require manual operation. A pneumatic, hydraulic, or electric actuator can be employed on certain configurations to provide for remote control of the valve by a human operator or automatic controller.
General valve functions include:
  • Flow start or stop
  • Flow rate increase or reduction
  • Diversion of flow in another direction
  • Regulation of a flow or process pressure

Industrial process control valves are often classified according to their mechanical movement. Some common examples include:
  • Linear motion valves, in which the closure element moves in a straight (linear) direction to control the flow. Gate, globe, and diaphragm valves are in this category.
  • Rotary motion valves have a closure that follows an angular or circular path. Butterfly and ball valves are in this group.
  • Quarter turn valves, a subset of the rotary motion class, traverse from the open to closed state when the closure element (for example, the ball in a ball valve) is rotated through a quarter of a full turn. This type is best suited for operations calling for either fully open or closed regulation, with no need for control at points in between those two states.

Each industrial control valve application and installation will have its own set of very specific requirements. The goal of the specification and selection process should be to provide safe operation, low maintenance requirements, robust and accurate operation. A manufacturer's sales engineer can be a useful source for application and specification information and assistance.
Oil Pipeline Valve
Ball Valve Installed in Pipeline
Courtesy DHV

Thursday, June 11, 2015

The Often Undervalued Sales Engineer

Call a sales engineer
Sales engineers add value.

Process and control equipment is most often sold with the support of sales engineers working for the local distributor or representative. Realizing what they have to contribute, and taking advantage of this available talent, will help you save time, cost, and also assist in achieving a better outcome for the project.

Consider these contributions:

Product Knowledge: Sales engineers, by the nature of their job, are current on new products, their capabilities and their proper application. Unlike information available on the Web, sales engineers get advanced notice of product obsolescence and replacement. Also, because they call and work with so many different types of companies, sales engineers are a wealth of tacit knowledge that they readily share  with their customers.

Experience: As a project engineer, you may be treading on fresh ground regarding some aspects of your current assignment. You may not have a full grasp on how to handle part of a control loop. Call in the local sales person - there can be real benefit in connecting to a source with past exposure to your current issue.

Access: Through a technical sales engineer, you may be able to look “behind the scenes” with a particular manufacturer and garner important information not publicly available. Sales reps deal with people, and make it his/her business to know what’s going on with products, companies, and industries.

Of course, sales engineers will be biased. Any solutions proposed are likely to be based upon the products sold by the representative. But the best sales people will share the virtues of their products openly and honestly, and even admit when they don’t have the right product. This is where the discussion, consideration and evaluation of several solutions become part of achieving the best project outcome.

As an engineer who designs or manufactures a product or process, it's highly recommended you develop a professional, mutually beneficial relationship with a technical sales expert. Look at a relationship with local sales engineer as symbiotic. Their success, and your success, go hand-in-hand.