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

Thursday, May 11, 2017

Rack and Pinion Actuator - Double Acting vs. Single Acting

pneumatic valve actuator
Pneumatic rack and pinion valve actuator
Courtesy Emerson - Hytork
Automating industrial valve operation requires numerous considerations in selecting the correct power source, drive type, torque range, and much more. The widest range of possible operation conditions should be anticipated and accommodated by the actuator selection to assure safe and effective valve operation under normal and adverse conditions.

The use of compressed air or gas as the energy source for valve positioning has been in use for many years and remains popular to this day. Among the perceived advantages of this energy source are the ability to store it in pressurized vessels for emergency short term use and the absence of any potential ignition source, as may be the case with electric powered actuators.

A rack and pinion valve actuator delivers a linear torque output throughout its full range of travel. The movement of a piston causes movement of the rack. The rack is toothed, and drives the pinion, converting linear movement of the rack into rotational movement of the pinion. The pinion is connected to the valve shaft, providing re-positioning of the valve. Adjustable stops, part of the actuator, limit the travel of the valve trim.

spring return and double acting valve actuator diagrams
Double acting pneumatic rack and pinion actuator (left) on its inward stroke. Spring return actuator (right) on its
outward or air powered stroke  (Illustrations courtesy of Emerson - Hytork) 

There are two common configurations of rack and pneumatic pinion actuators. A double acting actuator has provisions for delivering or exhausting air from both sides of the piston. Small control valves coordinate the delivery and removal of pressurized air or gas to drive the pistons inward or outward, producing torque in a clockwise or counterclockwise direction. Its operation could also be described as "air to open, air to close".

The single acting version of the pneumatic rack and pinion actuator provides air driven movement in only one direction. In this case, reversing the direction of travel is accomplished with a spring installed within the chamber on one side of the pistons. The spring powered movement provides a fail safe positioning of the valve in the case of control air pressure loss. This actuator provides "air to open, spring to close" operation, although, in some cases the fail safe position can be changed.

This is the simple version. Share your process control challenges with a valve expert, combining your own process knowledge and experience with their product application expertise to develop effective solutions.



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.



Monday, September 14, 2015

No Compressed Air? Use Water to Power Your Valve Actuator.

Hytork XLW Water Powered Valve Actuator
XLW Water Powered Valve Actuator
Courtesy Hytork
Air is everywhere, but very little of it is compressed for our use in powering a valve actuator. Sometimes, possibly at sites located remotely, a reliable source of compressed air is unavailable for process control valve actuation. Installing an air compressor at the site may be an option, but one with impact on the reliability of the installation deemed undesirable. One possible solution is a water powered valve actuator. With mains water available, pressurized within the range of 60 to 100 psi (4-7 bar), actuator power can be derived and valve operation successfully achieved.

Water always presents its own set of special considerations, not the least of which is that it tends to corrode most metals used in construction of actuator parts over time. Of additional concern are the particulates present in water systems which can cause premature deterioration of seals and scoring of cylinders in the actuator. Directional control solenoid valves will also function more reliably with a water supply free of larger particulates. While this is a concern, the solution is simply to place an inexpensive filter upstream of the devices, eliminating the contaminates from the water supply.

While it is possible to employ some "standard" actuators in a water powered setting, there are special adaptations that can be applied to common actuator design to better suit the use of water power. One manufacturer, Hytork, has done just that with their XLW Series of water operated actuators. The XLW Series is a water powered adaptation of the company's successful XL Series actuators. Special coatings are applied to critical parts to provide necessary protection for water applications. There are other differences between the compressed air and water versions of the actuator, detailed in the installation and operating instruction manual shown below. The manual is short enough to be read in a couple minutes (really, just a couple minutes) and provides useful and illustrative information about actuator construction, operating characteristics, and maintenance requirements.

Contact a valve application specialist for more information, or to discuss any of your fluid control application needs.