Control Valve Application Notes

Control Valve Application Notes

Using an incorrectly applied or sized control valve may have significant ramifications for operation, productivity, and, most importantly, safety. Here is a brief list of fundamentals to consider: 

Control valves are not isolation valves: 

Control valves do not isolate a process and do not offer a bubble-tight seal, and utilization in a shutoff capacity is unwise. 

Choose the suitable materials for the job: 

The valve body, seat, and wetted materials must all be compatible with the process under control. Before selecting a valve, evaluate the pressure ratings, operating temperatures, and material compatibility. 

Sensor placement: 

Place the flow sensor upstream of the control valve when configuring the control loop. When the flow sensor placement is downstream of the control valve, exposure to an unstable fluid (bubbles) created by the flashing and turbulence of the flow in the valve cavity is possible.

Control precision and mechanical constraints: 

Consider the degree of controllability you need and the inherent Deadband produced by your valve and associated components. Deadband is the built-in movement that occurs in a control valve between the signal change and the direction of the valve, which exacerbates by worn or poorly designed couplings between valve and actuator, mechanical sensor tolerances, friction in the valve stems and seats, or an undersized actuator. Due to opening/closing oscillations, too much deadband leads to poor controllability (hunting). 

Stiction: 

Stiction is the "stickiness" in valve action induced by packing gland, seat, or force against the disk friction. It may happen if the valve sticks in one position for a prolonged time or is constantly traveling in a minimal range for an extended period. The actuator must apply more force to break the disk free, resulting in overshoot and poor control. 

Tuning the loop controller and/or positioner: 

A poorly configured loop controller or positioner is often the source of poor control and loop instability. Advanced auto-tuning capabilities in PI (proportional with integral), PD (proportional with derivative), and PID (proportional with integral and derivative) controllers have replaced human (often trial and error) loop tuning. 

Valve sizing should be correct: 

Control valves are often oversized, permitting maximum flow at just a tiny percentage of total travel. Minor adjustments in valve position have a significant impact on flow. A high valve-position-to-flow ratio promotes continual "hunting," which leads to excessive valve wear. A decent rule of thumb is to size a control valve at around 70% to 90% of its travel. 

What sort of flow characteristics does your valve produce: 

The flow characteristic of a control valve is the connection between the position of the valve disk, gate, or globe and the change in flow rate through the valve under normal circumstances. A linear flow characteristic is desirable. However, different valve designs have varying flow characteristics, some of which are linear and others that are not. Globe control valves have linear flow properties, while butterfly and gate valves have non-linear flow characteristics. Manufacturers will often create specifically shaped disks or orifices to "characterize" the valve's flow to improve linearity.

The above is a brief list of the most common things to consider when applying control valves. There are many other criteria to consider. It is suggested in the strongest terms to consult with an experienced application expert before selecting or using a control valve.

Process Measurement, Valve, and Combustion Experts Serving Northern California and Nevada

Process Measurement and Control Solutions

CTi Controltech contributes a wealth of knowledge, experience, and skill in their customer engagements. The items we carry come from globally recognized manufacturers and are used in conjunction with our contracting and engineering resources to provide complete solutions to our customers' problems. A leading provider of valves, valve actuation, emissions control, and monitoring systems for industrial burners and boilers. CTi Controltech also provides custom SCR systems as well as steam management solutions. CTi Controltech, headquartered in San Ramon, California, serves Northern California and Nevada. We design solutions to the problems that our customers experience daily in process control.

Combustion, Emission and Steam Solutions 

  • Low and ultra low NOx burners and burner retrofits 
  • BMS and CMS system design and hardware 
  • Custom design SCR Systems 
  • Burner air fuel mix recalibration 
  • Pre-emission test and boiler tune-ups 
  • Heat rate, efficiency studies and plant improvement 
  • Vapor recovery 
  • Particulate and CO2 control 

Process Control and Combustion Services 

  • Factory trained service personnel 
  • Commissioning and startup technical support 
  • Technical seminars and training 
  • Valve and actuator calibration and startup 
  • Instrument calibration and startup 
  • Complete turnkey project capabilities 
  • U.L. 508 custom design 
  • Project CAD drawings 
  • PLC Programming 
  • CFD and modeling 

Process Control Instrumentation Solutions 

  • Flow, level, pressure, density and temperature

Valve, Actuation, and Automation Solutions 

  • Severe service valve sizing and selection 
  • Valve and actuation packages, pneumatic, hydraulic and electric 
  • Noise and cavitation control 
  • Total valve management programs 
  • Turbine by-pass 
  • Desuperheating and attemperation 
  • Damper drives 
  • Check valves 
  • Vent to atmosphere and silencers 
  • Best fit for purpose replacement recommendations 
  • Ease of operation and life cycle cost considerations 

Pressure Relief and Flame Mitigation Technology

  • Pressure/Vacuum Relief Valves 
  • Pressure Relief Valves 
  • Vacuum Relief Valves 
  • Pilot Operated Valves 
  • Flame and Detonation Arresters 
  • Emergency Relief Valves 
  • Waste Gas Burners 
  • Pressure Regulators  
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925-208-4250

Linear and Quarter-turn Industrial Valves

Linear and Quarter-turn Industrial Valves

Various valves are designed and used for multiple roles in process control. Linear and quarter-turn valves are two types of valves used to regulate and control fluid flow in the industry. Their design and construction reflect the intended use of the valves, with each suited to a different class of service. 

All valves work by controlling the position of an internal structure that obstructs fluid passage to some extent. In general, fluid flow at the valve classifies as unrestricted (valve fully open), stopped (valve fully closed), or throttled (valve partially open). The operational requirements of the process will determine whether only two of those conditions (fully open and fully closed) or all three are required. When choosing an appropriate valve, the fluid, the process, and the surrounding environment must be considered. It is not always a simple task. 

Linear valves distinguish themselves using straight-line motion to position the valve plug, disc, diaphragm, or other flow controlling elements. The linear valve trim's shape, size, and arrangement provide the operator with a flow range through the valve. The linear valve's positioning allows it to regulate fluid flow slower but more accurately. Linear motion valves include gate and fixed cone valves—linear valves best suit flow control.

Quarter turn valves move from fully open to closed by rotating a shaft connected to the controlling element 90 degrees. Their relatively simple operation allows for a rugged and compact design. The ability of quarter-turn valves to quickly reposition from open to closed positions is one of their distinguishing features. The torque required to operate the valves is typically low to moderate. Quarter turn valves include ball and butterfly valves. 

Depending on the situation, linear valves and quarter-turn valves are the best choices for specific process environments. The linear valve's accuracy and ability to move in a linear fashion rather than a quarter-turn come with easy maintenance and a lower likelihood of cavitation. Both valve types are widely used and are not competing for the same application. Each excels in a specific set of applications.

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925-208-4250

Alfa Laval's Unique Mixproof 3-Body Sanitary Valve

Alfa Laval's unique Mixproof 3-Body valves allow for the simultaneous flow of two different products or fluids through the same valve without the risk of cross-contamination. The valve also includes a changeover function. 

The Mixproof 3-Body valve offers optimal process flow, exceptional hygiene, maximum uptime, and a low total cost of ownership. Its modular, three-valve-body design ensures reliable fluid handling and safety, making it ideal for use as a hygienic changeover valve. The Mixproof 3-Body valve translates into significant cost savings and increased efficiency.

FEATURES:

  • Operating spillage-free
  • Simplified maintenance
  • High level of hygiene
  • Outstanding safety level
  • Based on proven platform

Alfa Laval manufactures sanitary valves and automation. Customers trust Alfa Laval valves in the food, biopharma, life science, pharmaceutical, and cosmetic industries for process performance and hygiene in the most demanding applications.

For more information about Alfa Laval valve products in Northern California and Northwestern Nevada, contact CTi Controltech by calling 925-208-4250 or visit https://cti-ct.com.