Showing posts with label pneumatic valve. Show all posts
Showing posts with label pneumatic valve. Show all posts

Thursday, July 27, 2017

Valve Positioners

industrial valve actuator with positioner
Valve positioner installed on pneumatic actuator
Courtesy Crane ChemPharma Energy
Valve positioners can provide process operators with a precise degree of valve position control across the valve movement range, as well as information about valve position. A relationship exists between applied pneumatic signal pressure and the position of the valve trim. The relationship between the two elements is dependent upon the valve actuator and the force of the return spring reacting to the signal pressure. In a perfect world, the spring and pneumatic forces would reach equilibrium and the valve would return to the same position in response to an applied signal pressure. There are other forces, however, which can act upon the mechanism, meaning the expected relationship between the original two elements of pressure and position may be offset. For example, the packing of the valve stem may result in friction, or the reactive force from a valve plug resulting from differential pressure across the area of the plug may be another.

While these elements may seem minor, and in some cases they are, process control is about reducing error and delivering a desired or planned output. Inclusion of a positioner in the valve assembly can ensure that the valve will be set in accordance with the controller commands.

Each positioner functions as a self-contained small scale control system. The first variable in the positioning process is the current valve position, read by a pickup device incorporated in the positioner. A signal which is sent to the positioner from the control system, indicating the desired degree of opening, is used as the setpoint. The controller section of the positioner compares the current valve position to the setpoint and generates a signal to the valve actuator as the output of the positioning process. The process controller delivers a signal to the valve, and then the positioner takes that signal and supplies air pressure required to accomplish the needed adjustment of the stem position. The job of the valve positioner is to provide compensatory force and to act as a counterbalance against any other variables which may impact valve stem position.

Magnetic sensors can be employed to determine the position of the valve stem. The magnetic sensor works by reading the position of a magnet attached to the stem of the valve. Other technologies can be employed, and all have differing ways of overcoming degrees of inaccuracy which may arise with wear, interference, and backlash. In addition to functioning as a positioner, control valve positioning devices can also function as volume boosters, meaning they can source and subsequently ventilate high air flow rates from sources other than their pneumatic input signal (setpoint). These devices can positively affect and correct positioning and velocity of the valve stem, resulting in faster performance than a valve actuator solely reliant on a transducer.

The inclusion of a positioner in a control valve assembly can provide extended performance and functionality that deliver predictable accurate valve and process operation. Share your valve automation requirements with a knowledgeable specialist and combine your process knowledge and experience with their product application expertise to develop an effective solution.

Tuesday, December 29, 2015

Pneumatic Actuator For Corrosive Environments

Corrosion Resistant industrial valve pneumatic Actuator disassembled
Commando XL Corrosion Resistant
Pneumatic Valve Actuator
Courtesy Hytork - Emerson
Industrial process control operations sometimes call for equipment to be placed in physical locations or environments that are not conducive to a long and productive component lifespan. Extremes of temperature, humidity, and vibration can have substantial effect on equipment performance and longevity. Deleterious impact can also arise from elements of the process itself, in the form of corrosive liquid or vapor prevalent in the processing area. While most industrial equipment is provided with some level of protection, there are instances where standard coatings and protective materials may not provide adequate resistance to the deteriorating impact of their installation environment.

Valves of many types are used throughout industrial processes to provide control of fluid flow, with quarter turn movement being one of the more prevalent.
Pneumatically powered quarter turn valves have an actuator option that provides a high level of corrosion resistance, along with the field proven performance of a recognized leading product. 
Hytork™, an Emerson brand, offers their XL line of actuators with a special treatment to withstand aggressively corrosive environments. The corrosion resistant version has been labelled "XL Commando" and, in the company's own words, has...
A durable Fluoropolymer impregnation (using CORROGARD-CG941) of the actuator body parts (inside and out) for maximum corrosion resistance. This durable impregnation can best be achieved in cast aluminum parts (all XL COMMANDO body parts are cast aluminum). As the aluminum metal grains are expanded under heat the CORROGARD-CG941 is applied, entering the grain structure and, upon cooling, is locked at the surface, integral with the grain structure. Extruded surfaces can only be coated and are more susceptible to scratches and other mechanical deterioration.
You can review the performance range, sizes, and other features of these pneumatic valve actuators through a review of the document included below. Bring your process challenges to a valve application specialist and combine your process knowledge with their product application expertise to achieve a solid practical solution.

Friday, July 25, 2014

The Virtues of Angle Seat Valves

Gemu angle seat valve
GEMU Angle Seat Valve
“Angle valves” or “angle seat valves” are a family of on-off and control valves that have utilize a “Y” pattern body style, and a linear action to raise the disk from the seat to open and close the valve. By positioning the seat on an angle, the piston is pulled out of the flow path clearing the way for maximum flow. Angle valve provides tight shutoff, high cycle rate capability and very long service life. Here are other design features that make an angle valve a top performer: