Sunday, May 31, 2015

5 Important Things to Consider Before Selecting a Remote Level Display

remote display
Pick the right remote display.
Level is one of the most commonly measured process values in a wide range of applications and industries. Available level transmitters range from mechanical floats and contact probes to radar and ultrasonic sensors. Whatever the type, these transmitters are almost universally difficult and dangerous to access. Even if a display is included, the small built‐in displays are difficult to read once installed. Including a remote level display showing easy to understand engineering units in a convenient location is a critical step in developing a level measurement solution.

Considering the following five topics will help you create a safe, effective, and efficient level measurement system. Including the right level display to accompany a level transmitter can have a dramatic impact.

Friday, May 29, 2015

Designing a Process Control Loop? Or maybe a Custom Thermal System? Call a Sales Engineer.

Tech Sales Engineer
Sales Engineers are a valuable,
readily available resource.
Are you an engineer tasked with designing a new control loop for a manufacturing line? Or perhaps you're an engineer at an OEM designing a new piece of equipment requiring an electric heater, control and sensor?

Call a sales engineer to make your job easier.

Projects and tasks are best completed and accomplished through the proper application of the right resources. There exists an access point to high level technical knowledge and assistance that can be easily tapped and brought to bear on your successful task or project completion.

Local distributors and representatives for process equipment and control manufacturers provide services that may help you save time and cost, while also achieving a better outcome for the entire project. Consider a few elements the technical sale rep brings to your project:

  • Product Knowledge: Sales engineers will be current on product offerings, proper application, and capabilities. They also have information regarding what products may be obsolete in the near future. This is an information source at a level not generally accessible to the public via the Internet.
  • Experience: As a project engineer, you may be treading on fresh ground regarding some aspects of your current assignment. 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 establish a connection to “behind the scenes” manufacturer contacts with essential information not publicly available. The rep knows people, makes it his/her business to know the people that can provide answers to your  application questions.

Certainly, any solutions proposed are likely to be based upon the products sold by the representative. That is where considering and evaluating the benefits of any proposed solutions become part of achieving the best project outcome.

Develop a professional, mutually beneficial relationship with a technical sales team. Their success is tied to your success and they are eager to help you.

Thursday, May 28, 2015

Demonstration of Cavitation and its Detrimental Impact on Control Valves

cavitation on control valve
Pressure drop causing cavitation.
Fluid passing through a control valve experiences changes in velocity as it enters the narrow constriction of the valve trim (increasing velocity) then enters the widening area of the valve body downstream of the trim (decreasing velocity). These changes in velocity result in the fluid molecules’ kinetic energies changing as well. In order that energy be conserved in a moving fluid stream, any increase in kinetic energy due to increased velocity must be accompanied by a complementary decrease in potential energy, usually in the form of fluid pressure. This means the fluid’s pressure will fall at the point of maximum constriction in the valve (the vena contracta, at the point where the trim throttles the flow) and rise again (or recover) downstream of the trim:

If fluid being throttled is a liquid, and the pressure at the vena contracta is less than the vapor pressure of that liquid at the flowing temperature, the liquid will spontaneously boil. This is the phenomenon of flashing. If, however, the pressure recovers to a point greater than the vapor pressure of the liquid, the vapor will re-condense back into liquid again. This is called cavitation.

As destructive as flashing is to a control valve, cavitation is worse. When vapor bubbles re-condense into liquid they often do so asymmetrically, one side of the bubble collapsing before the rest of the bubble. This has the effect of translating the kinetic energy of the bubble’s collapse into a high-speed “jet” of liquid in the direction of the asymmetrical collapse. These liquid “microjets” have been experimentally measured at speeds up to 100 meters per second (over 320 feet per second). What is more, the pressure applied to the surface of control valve components in the path of these microjets is intense. Each microjet strikes the valve component surface over a very small surface area, resulting in a very high pressure (P = F/A ) applied to that small area. Pressure estimates as high as 1500 newtons per square millimeter (1.5 giga-pascals, or about 220000 PSI!) have been calculated for cavitating control valve applications involving water.

Content courtesy of Tony R. Kuphaldt

Wednesday, May 20, 2015

Electric Heating Element Types and Selection Guide

The following, courtesy of Hotwatt,  is a good reference for selecting an electric heating element for both OEM and process heating applications.

Included are all types of industrial electric heaters - cartridge, band, tubular, immersion, duct, circulation and cable.

Tuesday, May 12, 2015

Cashco Ranger Control Valve: How to Change Signal Loss Mode of Failure

This video explains in detail how to change the Cashco Ranger control valve loss of signal failure mode from air to open / fail closed to air to close/ fail open, as well las remounting and recalibrating the valve positioner.

The Cashco Ranger is one of the most popular control valves on the market. It is the most versatile, adaptable, and easily maintainable valve ever produced. No other valve is more user friendly.

The Ranger offers over 6 different trim combinations. Trim can easily be changed in less than 5 minutes without disturbing the packing, actuator, or positioner calibration. The service area is a thread-less design, which resists corrosion or collection of chemical deposits.

A selection of 3 body materials with a broad temperature range from -325°F to +750°F makes the Ranger adaptable for use in steam, heat transfer fluids, slurries, gases, liquids, and cryogenic applications. The Ranger’s unique dual seating design provides both Class VI and backup Class IV seat leakage. And the standard patented live-loaded packing system lets you check and adjust packing without the need for specialized tools or complicated procedures.

For more information about Cashco in Northern California, contact:

Belilove Company Engineers
P.O. Box 55936
21060 Corsair Blvd
Hayward, CA 94545
Phone: (510) 274-1990
Fax: (510) 274-1999

Friday, May 1, 2015

Chlorine Analyzers in Wastewater Treatment

chlorine analyzer
Chlorine Analyzer
The reliable, efficient, and environmentally-friendly operation of wastewater treatment frequently requires continuous analysis of the process's inputs, reactions, and outputs. These analyses may be for the detection or monitoring of: impurities; purity; turbidity; blending; quality; color or some other key chemical, such as chlorine. Regardless of the chemical or trait being monitored, the applications always require the utmost in analyzer reliability and durability to help ensure continuous, quality process operations.

Wastewater Treatment - Disinfection Example

The final step in treating wastewater before releasing it into the natural environment is to kill any harmful microorganisms (e.g. viruses, bacteria) in it. This is called disinfection, and chlorine gas is a very effective disinfecting agent. However, just as it is not good to mix too little chlorine in the outgoing water (effluent) because we might not disinfect the water thoroughly enough, there is also danger of injecting too much chlorine in the effluent because then we might begin poisoning animals and beneficial microorganisms in the natural environment. 

To ensure the right amount of chlorine injection, we must use a dissolved chlorine analyzer to measure the chlorine concentration in the effluent, and use a controller to automatically adjust the chlorine control valve to inject the right amount of chlorine at all times. The following P&ID (Process and Instrument Diagram) shows how such a control system might look:

Chlorine gas coming through the control valve mixes with the incoming water (influent), then has time to disinfect in the contact chamber before exiting out to the environment. 

The transmitter is labeled “AT” (Analytical Transmitter) because its function is to analyze the concentration of chlorine dissolved in the water and transmit this information to the control system. The “Cl2” (chemical notation for a chlorine molecule) written near the transmitter bubble declares this to be a chlorine analyzer. The dashed line coming out of the transmitter tells us the signal is electric in nature, not pneumatic as was the case in the previous (boiler control system) example. The most common and likely standard for electronic signaling in industry is 4 to 20 milliamps DC, which represents chlorine concentration in much the same way as the 3 to 15 PSI pneumatic signal standard represented steam drum water level in the boiler:

chlorine control valve
Chlorine Control

The controller is labeled “AIC” because it is an Analytical Indicating Controller. Controllers are always designated by the process variable they are charged with controlling, in this case the chlorine analysis of the effluent. “Indicating” means there is some form of display that a human operator or technician can read showing the chlorine concentration. “SP” refers to the setpoint value entered by the operator, which the controller tries to maintain by adjusting the position of the chlorine injection valve. 

A dashed line going from the controller to the valve indicates another electronic signal: a 4 to 20 mA direct current signal again. Just as with the 3 to 15 PSI pneumatic signal standard in the pneumatic boiler control system, the amount of electric current in this signal path directly relates to a certain valve position:

Note: it is possible, and in some cases even preferable, to have either a transmitter or a control valve that responds in reverse fashion to an instrument signal such as 3 to 15 PSI or 4 to 20 milliamps. For example, this valve could have been set up to be wide open at 4 mA and fully shut at 20 mA. The main point to recognize here is that both the process variable sensed by the transmitter and the position of the control valve are proportionately represented by analog signals.

Just as with the 3 to 15 PSI pneumatic signals used to represent water level and control valve position in the boiler seen previously, the two 4 to 20 milliamp current signals in this system represent two different variables in the system and therefore will not be equal to each other except by coincidence. A common misconception for people first learning about analog instrumentation signals is to assume the transmitter’s signal (“Process Variable”) must be identical in value to the control valve’s signal (“Manipulated Variable” or “Output”), but this is not true.

The letter “M” inside the control valve bubble tells us this is a motor-actuated valve. Instead of using compressed air pushing against a spring-loaded diaphragm as was the case in the boiler control system, this valve is actuated by an electric motor turning a gear-reduction mechanism. The gear reduction mechanism allows slow motion of the control valve stem even though the motor spins at a fast rate. A special electronic control circuit inside the valve actuator modulates electric power to the electric motor in order to ensure the valve position accurately matches the signal sent by the controller. In effect, this is another control system in itself, controlling valve position according to a “setpoint” signal sent by another device (in this case, the AIT controller which is telling the valve what position to go to).

("Disinfection Example" courtesy of Tony R. Kuphaldt )