Tuesday, January 31, 2017

The Rack and Pinion Style Pneumatic Actuator

pneumatic rack and pinion valve actuator
Pneumatic Rack and Pinion Valve Actuator
Courtesy Emerson - Hytork
Three primary kinds of valve actuators are commonly used: pneumatic, hydraulic, and electric.

Pneumatic actuators can be further categorized as scotch yoke design, vane design, and the subject of this post - rack and pinion actuators.

Rack and pinion actuators convert linear movement of a driving mechanism to provide a rotational movement designed to open and close quarter-turn valves such as ball, butterfly, or plug valves and also for operating industrial or commercial dampers.


Rack and Pinion Animation
Courtesy Wikipedia
The rotational movement of a rack and pinion actuator is accomplished via linear motion and two gears. A circular gear, known as a “pinion” engages the teeth of one or two linear gears, referred to as the “rack”.

Pneumatic actuators use pistons that are attached to the rack. As air or spring power is applied the to pistons, the rack changes position. This linear movement is transferred to the rotary pinion gear (in both directions) providing bi-directional rotation to open and close the connected valve.

Rack and pinion actuators pistons can be pressurized with air, gas, or oil to provide the linear the movement that drives the pinion gear. To rotate the pinion gear in the opposite direction, the air, gas, or oil must be redirected to the other side of the pistons, or use coil springs as the energy source for rotation. Rack and pinion actuators using springs are referred to as "spring-return actuators". Actuators that rely on opposite side pressurization of the rack are referred to as "direct acting".

Most actuators are designed for 100-degree travel with clockwise and counterclockwise travel adjustment for open and closed positions. World standard ISO mounting pad are commonly available to provide ease and flexibility in direct valve installation.

NAMUR mounting dimensions on actuator pneumatic port connections and on actuator accessory holes and drive shaft are also common design features to make adding pilot valves and accessories more convenient.

Pneumatic pneumatic rack and pinion actuators are compact and effective. They are reliable, durable and provide good service life. There are many brands of rack and pinion actuators on the market, all with subtle differences in piston seals, shaft seals, spring design and body designs. Some variants are specially designed for very specific operational environments or circumstances.

Share your process valve control and automation challenges with application experts, and combine your process experience and knowledge with their product application expertise to develop effective solutions. 

Monday, January 23, 2017

Appropriate Application for Pressure Regulator Valve and Back Pressure Regulator

back pressure regulator valve
One of many variants of back pressure
regulator valves
Courtesy Cash Valve
Fluids move throughout processes, driven by pressure produced with mechanical or naturally occurring means. In many cases the pressure generated by the driving source is substantially greater than what may be desired at particular process steps. In other cases, the operation may dictate that a minimum pressure be maintained within a portion of the process train. Both cases are handled by the appropriate valve type, designed specifically to regulate pressure.

A pressure regulating valve is a normally open valve that employs mechanical means, positioning itself to maintain the outlet pressure set on the valve. Generally, this type of valve has a spring that provides a countervailing force to the inlet pressure on the valve mechanism. An adjustment bolt regulates the force produced by the spring upon the mechanism, creating an equilibrium point that provides flow through the valve needed to produce the set outlet pressure. A typical application for a pressure regulator is to reduce upstream or inlet pressure to a level appropriate for downstream processing equipment.

Back pressure valves are normally closed, operating in a logically reversed fashion to pressure regulators. Where pressure regulators control outlet pressure, a back pressure valve is intended to maintain inlet pressure. Similar internals are present in the back pressure valve, with the valve action reversed when compared to a pressure regulator. An inlet pressure reduction in the back pressure valve will cause the valve to begin closing, restricting flow and increasing the inlet pressure. A representative application for a back pressure valve is a multi-port spray station. The back pressure valve will work to maintain a constant setpoint pressure to all the spray nozzles, regardless of how many may be open at a particular time.

Both of these valve types are available in an extensive array of sizes, capacities, pressure ranges, and materials of construction to accommodate every process requirement. Share your fluid control challenges with a process control specialist. Combining your process knowledge with their product application expertise will produce effective solutions.

Wednesday, January 18, 2017

Mountain States Engineering and Controls Expands Product Offering

duplex condensate return pump with receiver tank and sight glass
Duplex condensate return pump
Courtesy Sterling Sterlco
Mountain States Engineering and Controls has added the Sterling Sterlco line of condensate pump, boiler feed pump, and temperature control valve products to round out its comprehensive offering of instruments and equipment for steam systems and process cooling.

The Sterlco condensate pumps are available in simplex or duplex configurations, with pump and receiver capacity ratings to accommodate a broad range of industrial and commercial applications. Option selections round out the flexible product specification.

Boiler feed pump units from Sterlco provide a similar extensive range of receiver and pump capacities, along with options to meet application specific requirements.

The Sterlco self powered modulating temperature control valves are available in eight sizes and provide regulation of coolant flow to a machine or process. Their simple design provides rugged temperature actuated performance in a wide array of cooling applications.

There is more to learn about Sterling Sterlco condensate pumps, temperature control valves, and boiler feed pumps. For the latest product information, or to work on a solution to your steam or cooling system challenges, reach out to an application expert and combine your facilities and process knowledge with their product application expertise to develop effective solutions.



Monday, January 9, 2017

Summary of Technologies Used For Continuous Liquid Level Measurement in Industrial Process Control

differential pressure transmitter with purge control for downpipe measurement
Differential pressure liquid level transmitter with
integrated downpipe purge control (bubbler method)
Courtesy King-Gage
Automated liquid processing operations in many fields have requirements for accurate and reliable level measurement. The variety of media and application criteria demand continuous improvement in the technology, while still retaining niches for older style units utilizing methods that, through their years of reliable service, inspire confidence in operators.

Here is a synopsis of the available technologies for instruments providing continuous liquid level measurement. All are generally available in the form of transmitters with 4-20 mA output signals, and most are provided with additional outputs and communications. What is notably not covered here are level switches or level gauges that do not deliver a continuous output signal corresponding to liquid level.

Whether considering a new installation or upgrading an existing one, it can be a good exercise to review several technologies as possible candidates for a project. None of the technologies would likely be considered the best choice for all applications. Evaluating and selecting the best fit for a project can be facilitated by reaching out to a product application specialist, sharing your applications challenges and combining your process knowledge with their product expertise to develop an effective solution.

Displacer – A displacer is essentially a float and a spring that are characterized for a particular liquid and range of surface level movement. The displacer moves in response to liquid level, changing the location of a core connected to the displacer by a stem. The core is within a linear variable differential transformer. The electrical output of the transformer changes as the core moves.

Guided Wave Radar – A radar based technology that uses a waveguide extending into the liquid. The radar signal travels through the waveguide, basically a tube. The liquid surface level creates a dielectric condition that generates a reflection. Calculations and processing of the emitted and returned signals provide a measure of distance to the liquid surface. No moving parts.

Magnetostrictive – A method employing measurement of the transit time of an electric pulse along a wire extending down an enclosed tube oriented vertically in the media. A magnetic float on the exterior of the tube moves with the liquid surface. The float’s magnetic field produces the return signal to the sensor. Processing the time from emission to return provides a measure of distance to the liquid surface.

Pulse Burst Radar - A radar based technology employing emissions in precisely timed bursts. The emission is reflectex from the liquid surface and transit time from emission to return is used to determine distance to media surface.  Not adversely impacted by changes in media conductivity, density, pressure, temperature. No moving parts.

Frequency Modulated Continuous Wave Radar – Another radar based technology that employs a radar signal that sweeps linearly across a range of frequencies. Signal processing determines distance to media surface.  Not adversely impacted by changes in media conductivity, density, pressure, temperature. No moving parts.

RF Capacitance - As media rises and falls in the tank, the amount of capacitance developed between the sensing probe and the ground reference (usually the side metal sidewall) also rises and falls. This change in capacitance is converted into a proportional 4-20 mA output signal. Requires contact between the media and the sensor, as well as a good ground reference. No moving parts.

Ultrasonic Non-Contact – Ultrasonic emission from above the liquid is reflected off the surface. The transit time between emission and return are used to calculate the distance to the liquid surface. No contact with media and no moving parts.

Differential Pressure – Pressure sensor at the bottom of a vessel measures the pressure developed by the height of the liquid in the tank. No moving parts. A variation of this method is often called a bubbler, which essentially measures hydrostatic pressure exerted on  the gas in a tube extending into the contained liquid. It has the advantage of avoiding contact between the measuring instrument parts, with the exception of the dip tube, and the subject liquid.

Laser - Probably one of the latest arrivals on the liquid level measurement scene, laser emission and return detection is used with time interval measuring to accurately determine the distance from the sensor source to the liquid surface.

Load Cell - A load cell or strain gauge can be incorporated into the support structure of the liquid containing vessel. Changes in the liquid level in the vessel are detected as distortions to the structure and converted, using tank geometry and specific gravity of the liquid.

All of these technologies have their own set of attributes which may make them more suitable to a particular range of applications. Consulting with a product specialist will help determine which technologies are the best fit for your application.

Monday, January 2, 2017

Steam Trap Maintenance Made Easier With Pipeline Connector

steam trap isolation valve set
PC4000 Pipeline Connector
Courtesy Spirax Sarco
Steam is a common source of heat or power throughout industrial and commercial installations. Most steam systems operate as a closed system, with return of condensate to maximize energy efficiency and gain other operational benefits. Steam traps are the workhorse of many condensate return systems, routing condensate back to the boiler and non-condensible gases out of the system, all without a major loss of steam.

Steam traps are points of high maintenance in the steam system. They are also an integral part of the system, meaning they are under pressure. Steam trap maintenance requires isolating the trap from the system, venting the pressure within the isolated section, and removing liquid that may be contained in the trap.

Spirax Sarco, globally recognized leader in steam system componentry and controls, provides a single unit solution for steam trap maintenance isolation. The PC4000 pipeline connector series (in the company's own words)...
"...are a complete 'Trap valve station solution' developed for use with two bolt universal swivel connector steam traps.
As the unit has been designed with two integral piston stop valves, it is possible to isolate both upstream and downstream of the universal trap connection and through the use of the fitted depressurization valves, possible to depressurize, test and drain the pipeline. The trap depressurization port also incorporates a maintainable 40 mesh stainless steel strainer screen to provide trap protection from system dirt and debris, which can be cleared through the use of the line pressure."
 A detailed data sheet is provided below for further review. Share your steam system challenges of all types with specialists, combining your facility and process knowledge with their product application expertise to develop effective solutions.