What Are Valve Positioners?

Digital Positioner (Valtek)

A valve positioner is used in combination with a valve actuator to precisely position a valve so that optimum flow accuracy may be achieved. The positioner does this by measuring a the process variable, comparing it to a desired condition (set point) and then pneumatically, electrically, or hydraulically changing the valve disc, globe, plug or ball position until the difference between the set point and actual position is zero.

Valve positioners are key elements in a closed loop control system where the final control element is a valve. They assist in maintaining tight control, overcoming the realities of imprecise calibration, differential pressure across the valve, valve wear and a host of other process control challenges.

A valve positioner responds to a signal from some type of master control system, typically a distributed control system (DCS), a programmable logic controller (PLC), or PID controller. The control system reads a signal from a process sensor (flowmeter, temperature sensor, pressure sensor, etc...) and compares that reading to the desired setpoint. A corrective signal, based on the difference,  is provided to the valve positioner which re-adjusts (if necessary) the valve position to bring the system in to equilibrium.

Valve positioners are available with pneumatic, electrical, electro-pneumatic, and digital operation. Here is a brief description of each:

Pneumatic

Pneumatic Positioner (Valtek)

Pneumatic positioners receive pneumatic signals (3-15 or 6-30 PSIG). The positioner then throttles supply air to the valve actuator to move the valve to the required position. Pneumatic positioners are intrinsically safe and can provide a large amount of force to close a valve.

Electric
Electric valve positioners receive an electric signal, usually 4-20 mA, 1-5 VDC, 2-10 VCD or 0-10 VDC and generally drive the motors in electric actuators. They perform the same function as pneumatic positioners do, but use electricity instead of air pressure as an input signal.

Electro-Pneumatic

Electro-pneumatic Positioner
(PMV)

Electro-pneumatic valve positioners contain internal I/P (current to pneumatic) modules that converts the electrical input signal to a pneumatic output (4-20 mA to 3-15 PSIG for instance). Very similar to a pneumatic positioner except that its input is electrical.

Valve positioners are used throughout the process industries including power, pharmaceutical, chemicals, oil and gas, food and beverage, pulp and paper, refining and petrochemicals, pipelines, and many other processes.

For more information on valve positioners, contact Swanson Flo by visiting https://swansonflo.com or by calling 800-288-7926.

Properties of Fluids: The Basics

This video introduces the viewer to basic fluid properties such as viscosity, viscosity index, compressibility, cleanliness, filtration and additives. These basics apply throughout process control, from flow instrumentation to valve automation.

Founded in 1960, Swanson Flo has long maintained our position as an industry leader in process automation with unmatched project success leveraging industry preferred products and services.

https://swansonflow.com
800-288-792

Limitorque Pneumatic Compact Scotch Yoke Actuator Model LPC

The Limitorque Pneumatic Compact (LPC) range is a robust, lightweight, modular Scotch yoke design available in both spring return and double acting configurations. It is suitable for actuating ball, butterfly and plug valves or any other quarter-turn application.

LPC compact actuators deliver up to 5500 Nm (4057 ft-lb) of precisely controlled torque. The LPC product range is complementary to the Limitorque LPS heavy-duty pneumatic Scotch yoke actuators.

A similar design philosophy to the heavy-duty LPS was applied to the new LPC range, delivering enhanced performance and high reliability. The LPC is available in standard as well as special material configurations upon request.

For more information, review the embedded document below, or you can download a PDF version of "Limitorque Model LPC Pneumatic Compact Scotch Yoke Actuator" here.

Limitorque Pneumatic Compact Scotch Yoke Actuator Model LPC from Swanson Flo

Vortex Flowmeters by Schneider Electric / Foxboro

Schneider Electric / Foxboro Vortex flowmeters in field.

Foxboro flowmeters set industry standards in applications requiring accuracy for totalizing and batching in utility metering of fluids. They are ideal for applications within upstream and downstream oil and gas industries, specifically on high-pressure pipeline applications.

Vortex flowmeter.

Foxboro flowmeters are the highest performing flowmeters on the market, with best-in-class sensing technology. No other competitor's meter can measure accuracy and liquid gas or steam for temperatures up to 800 degrees Fahrenheit. These instruments are designed to be flexible and reliable in harsh process environments. Foxboro vortex flowmeters have unique vortex sensing, with a lifetime warranty, patented algorithms that improve performance and real-world applications. A broad offering of sizes, material, and end connections with the widest flow range available today. Ease of configuration using FTD technology and no moving parts ensures low operating and maintenance costs.

Foxboro vortex transmitters have an on-board LCD indicator configurator for local configuration, and are equipped with Foxboro's patented DirectSense technology, which incorporates the sensor directly into the flow stream to maximize the vortex pull strength. This results in wider rangeability, greater noise immunity, along with unmatched sensitivity. With the Foxboro vortex flowmeter you achieve reliability, repeatability, and a measurement you can trust.

LCD indicator

For more information on Schneider Electric / Foxboro vortex flowmeters please visit Swanson Flo at https://swansonflow.com or by calling 800-288-7926.

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A Process Industry Stalwart - The Plug Valve

Lubricated plug valve.
(Flowserve Durco)

This article will focus on one of the oldest and most reliable (when properly applied) industrial valve types - the plug valve.

Fluid process control operations commonly employ pumps, piping, tanks and valves as the means of transporting, containing and controlling the fluid movement through a system.

Valves, of which there are many types, provide control over the flow rate, direction and routing of fluids in a processing operation. Flow can be started, stopped or modulated between zero and full rate using a properly sized and configured valve. Some valves enable media flow to be diverted to a selection of outlets, in lieu of a single inlet and outlet pair. Specialized valves regulate inlet or outlet pressure, or prevent fluid flow from going in an undesirable direction. All of these capabilities are packaged into differing valve product offerings that present a very large selection array to a process designer or engineer.

Non-lubricated plug valve.
(Flowserve Durco)

Industrial flow control valve types are generally classified according to the structure or arrangement contained within the valve body that provides obstruction to fluid flow. Some of the common types are ball, butterfly, gate, globe, and plug. Surely, there are more valve types, and this article is not intended to list them all. Some of our previous blogs have discussed selection considerations for gate, ball and butterfly valves.

Plug valves, like ball and butterfly valves, span from fully open to fully closed positions with a shaft rotation of 90 degrees. The “plug” in a plug valve is installed in the flow path within the valve body and rotated by means of a stem or shaft extending to the exterior of the body. Plugs are tapered toward the bottom and are fitted to a seating surface in the valve body cavity that prevents fluid from bypassing the plug. An opening through the plug, the port, can be shaped to provide particular flow characteristics. There are two main types of basic plug, lubricated and non-lubricated. Lubricated plug valves have a cavity into which a sealant is injected. The sealant provides a renewable seal between the plug and the body, prevents internal leakage, and protects the seating surfaces against corrosion. Non-lubricated plug valves utilize an elastomeric body liner or a sleeve in the body cavity that is pressed in to the body of the valve by the plug's wedge-like shape,  with the result of reducing the friction between the plug and the body.

Plug valve considerations:

• 90 degree rotation from open to closed provides fast operation.
• With proper configuration, can be well suited for frequent operation.
• Availability of corrosion resistant liner may provide comparative cost savings because valve body can be constructed of less expensive material.
• Design is simple and employs a low parts count.
• Valve can be serviced in place.
• Generally, low resistance to flow when fully open.
• Reliable leak-tight service due to tapered plug wedging action, replaceable sleeve, and injection of lubricant in some variants.
• Potential issues of concern for plug valve application include a short list of items.
• Higher friction in the plug closure mechanism may require comparatively higher operating torque than other valve types.
• Without a specially designed plug, generally not well suited for throttling applications.
• Rapid shutoff delivered by plug design may not be suitable for some applications where hammering may occur.

Share your fluid control application challenges with a valve and automation specialist. Leverage your own knowledge and experience with their product application expertise to develop an effective solution.

A Peek Inside a Valtek Mark One Control Valve with Piston Actuator

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

The Flowserve 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.

https://swansonflo.com
800-288-7926