Technical Article
Fig. 4. Diaphragm valves.
( Fig. 3). These valves do not restrict flow, but they can also act as an on / off valve while changing its direction.
• Overpressure protection valves: These valves prevent system pressure from increasing beyond a predetermined limit. Safety valves and rupture discs are the most common devices that perform this function. Relief valves can be calibrated to open automatically at a predetermined pressure level, ensuring system safety in the event of overpressure.
• Excess flow control valves: These valves activate when the flow through the valve reaches a predetermined value. These valves prevent the uncontrolled release of system media, preventing fluid from escaping rapidly. When an overflow condition occurs downstream, a mechanism within the valve quickly triggers, stopping most of the uncontrolled release of fluid.( Fig. 3)
Choosing the right valve: STAMPED methodology
Selecting the right valve for industrial fluid systems is a critical part of proper design and maintenance practices. The wrong valve selection can lead to poor system performance, increased downtime and preventable safety risks. Valve selection is typically made during the initial design phase of the system and rarely changes throughout its lifespan. Therefore, making the right choice from the outset is crucial. Designers and technicians can use the STAMPED method for proper valve selection. This methodology considers seven key operational conditions: Size: The valve’ s size determines its flow capacity and must be compatible with the system’ s required flow rate. The Kv value is a critical parameter in valve sizing. The size and geometry of the flow path within the valve directly impacts flow capacity. For example, while globe valves offer minimal flow resistance, needle valves can restrict flow.
Temperature: Both the system fluid temperature and the surrounding ambient temperature must be considered. Temperature fluctuations can cause expansion and contraction of sealing materials. High temperatures can reduce the strength of metallic components and lower pressure ratings. Manufacturer data should be reviewed to ensure the valve has been fully tested within the specified temperature range. Application: The function the valve will perform in the system( opening / closing, flow control, diverting, protection) must be determined. This directly impacts the type of valve selected. For example, needle or metering valves may be more suitable than ball valves for throttling or regulating flow. Media: The chemical makeup of the process fluid must be compatible with the materials of the valve body, seats, seals and other components. Incompatibility can lead to problems such as corrosion, embrittlement or stress corrosion cracking, creating safety risks and costly production issues. Additionally, the valve’ s resistance to outdoor conditions( sunlight, rain, seawater exposure) must also be considered. Pressure: Two primary types of pressure must be considered: working pressure( the normal pressure in the system) and design pressure( the maximum pressure limit specified by the manufacturer). The pressure limitation of a fluid system is based on its lowest-order component. Pressure and temperature are interrelated; generally, working pressure decreases as temperature increases. Ends: The way the valves connect to the piping system( integrated pipe fittings, pipe threads, flanges, welded ends, etc.) is important. Proper end connections simplify installation and reduce potential leak points. Ensure that the connections are suitable for the system pressure and temperature. Delivery: Finally, the timely and reliable supply of valves is as important as any other factor in keeping the fluid system operational and efficient. This ensures that projects remain uninterrupted and maintenance needs are met. To ensure these requirements are met, supply chain reliability must be taken into consideration. STAMPED Approach( Summary) The STAMPED methodology systematically evaluates seven key parameters for selecting the appropriate valve for the application( ISA, 2021):
Criterion
S( Size)
Explanation
Valve diameter and Kv value are determined according to flow capacity.
T( Temperature)
A( Application)
M( Media)
P( Pressure)
E( Ends)
D( Delivery)
Fluid and ambient temperature are taken into account in terms of material expansion and compatibility of seals.
The functions of the valve, such as opening / closing, control and steering, are determined.
The chemical structure of the fluid must be compatible with the material of the valve body and seals.
Working and design pressures must be considered together with material strength.
Connection types such as flange, threaded, and welding should be selected to be compatible with the system.
Procurement time and logistics suitability should be evaluated according to the project schedule.
This methodology minimises the margin of error in the selection process of technical teams while also reducing long-term operating costs.
Conclusion
Industrial valves are the fundamental building blocks that ensure the safety, efficiency, and control of fluid systems. Choosing the right valve is a critical step in complex engineering processes, ensuring trouble-free operation throughout the life of the system. Adopting a comprehensive approach like the STAMPED methodology will help engineers and technicians find reliable and cost-effective valve solutions tailored to the unique requirements of each application. This approach both optimizes operational performance and minimizes potential security risks.
References Crane Co.( 2018). Flow of Fluids Technical Paper No. 410, Crane Engineering.
ISA – International Society of Automation( 2021). Control Valve Handbook, 5th Ed.
American Petroleum Institute( API).( 2014). Recommended Practice 520: Sizing, Selection, and Installation of Pressure-Relieving Devices.
Perry, R. H., & Green, D. W.( 2019). Perry’ s Chemical Engineers’ Handbook, 9th Ed., McGraw-Hill.
ASME( 2016). Boiler and Pressure Vessel Code, Section VIII, Division 1.
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