The control valve performs a substantial role in establishing and maintaining an efficient process. When deciding on among the many obtainable choices, be positive to evaluate how the management valve’s features match the application’s fluid necessities when it comes to versatility, steady flow control, capability to deal with a variety of flows and connectivity for distant monitoring. Also search for characteristics that make it easier to maintain. Of the obtainable choices, rotary valves and linear angle valves supply widespread applicability.
Process management valve fundamentals
Control valves alter fluid circulate by varying the size of the circulate passage as directed by a sign from a controller. This allows the direct control of circulate price and the consequential control of key process parameters, including stress, temperature and liquid degree.
Several main types of control valves are available; each has professionals and cons and may be most appropriate for various applications. Finding the valve that works greatest for a selected application is a problem. Key considerations regarding technical specification embrace the level of management offered, resolution achieved and the valve’s supply time. Maintenance and longevity also wants to be considered. ราคาเกจวัดแรงดันน้ำ come into play throughout choice, including the necessity for application-specific data and experience, financial restrictions, plant outage schedules and upkeep plans over the life of the valve.
Options available
Linear globe valves are used for their versatility to manage circulate over a wide range, capability to mitigate noise and because they provide simpler access to valve internals throughout upkeep. They usually encompass a disk or cylindrical plug element with a stationary ring seat in a usually spherical physique. Globe valves embody stem-guided, cage-guided and top- and bottom-guided varieties. Stem- and top/bottom-guided valves are higher fitted to general industrial and less-aggressive applications. Cage-guided valves tend to be more costly, but carry out in a broader scope of functions and have extra flexibility to incorporate noise or cavitation mitigating features. All varieties may be controlled by electrical, pneumatic, guide or hydraulic means of actuation.
Linear angle valves are similar to globe-style valves, however are better fitted to essentially the most severe purposes with giant move rates, noise and flashing, because the mitigating expertise can be extra efficiently sized and integrated into the plant system. Stem-guided and cage-guided choices are supplied and actuation is often pneumatic or hydraulic because of the high internal forces and speedy response essential in these functions.
A linear three-way management valve has one inlet and two retailers or vice versa and is used in industrial applications. This permits mixing of liquids from two pipes into one pipe, or separating water from one pipe into two pipes. Typical functions embrace air-handling units, water chillers, boilers and fan coils. This possibility is usually supplied in stem-guided and cage-guided choices. It is typically not used for essentially the most extreme purposes, however somewhat to control the quantity of circulate or stress in one part of the piping system with respect to another.
Finally, rotary valves use the rotation of a passage or passages in a transverse plug to regulate the flow of liquid or fuel. Rotary valves have a extensive range of applicability, relying on the expertise incorporated within the internals. Globe and even angle valves have a relatively torturous flow path, which requires more stress drop to achieve a given flow, all other parameters being equal. A rotary valve can supply an inline, much less torturous path, while nonetheless offering comparable flow control, rangeability and resilience in severe-system conditions. Its structure supplies inherent benefit in situations where the working fluid accommodates solids and cleanliness cannot be maintained. These situations would have a extreme impression on globe or angle valve performance.
Table 1 supplies a common overview of the standard applications for which each management valve type is most suited. Rotary valves supply by far the most widespread applicability; linear angle valves are additionally applicable for a variety of purposes.
Table 1. General overview of the standard functions for which every control valve sort is most suited
Other components affecting management valve choice
Industry and country requirements, including American Society of Mechanical Engineers (ASME), Canadian Registration Number (CRN), Pressure Equipment Directive (PED) and American Petroleum Institute (API), amongst others, can affect the suitability of certain valve selections. In addition, selection of the management valve for an application is affected by various customer expectations — finish customers, engineering-procurement-construction (EPC) contractors and installation contractors have varying priorities in selection standards. Of these factors of view, the most important is the end user, who needs a management valve that provides the required management with the highest ease of use and maintenance over the valve’s life.
Features to search for in a management valve
During the choice process, look for and evaluate how the options into account meet these key features:
Versatility and ruggedness — Can the valve handle the full breadth of circumstances between the minimal and maximum specified conditions? Is it strong sufficient to resist upset conditions? Does it offer long service life without maintenance?
Works equally well on clear, dirty, viscous, corrosive, abrasive, high pressure/temperature fluids liquids and gases — Standardization throughout the install base helps with maintenance requirements and spare components stock. Adding filtering and cleansing of the working fluid in a system is sweet follow, nevertheless it additionally increases upkeep of those filters, which have to be considered in system design.
Stable move management — Consistent control in all situations is important. Inconsistency in control will lead to manufacturing downtime and loss of product.
Meets acceptable linear, equal proportion or other control characteristics — Different course of situations require: completely different management characteristics. Know the traits required and evaluate and confirm the management valve meets them.
Rangeability — Make positive the valve can handle all flow adjustments in the process.
Connectivity to a building/process administration system — Remote monitoring and management is important to processing applications. Ensure the valve is appropriate with the building/process administration system.
Features to make sure proper control valve maintenance
In addition to deciding on valves that meet the standards discussed above, it is essential the valves have options that guarantee correct maintenance. Here are the necessary thing options to look for:
Self-aligning seat ring for tight shutoff, no shimming or hardened materials
Access to the packing for inspection and adjustment
Splined or coupled shaft connections that enable ease of connect/disconnect from actuation
Blowout-proof shaft protection
Enclosed and self-purging actuator linkage
Ability to work on the valve without having to remove the physique from the system
The valve’s capacity to keep up tight shutoff to reduce loss of working fluid when it’s not wanted downstream of the valve. Keep in thoughts that control valves are not isolation valves, so do not use them in lieu of correct isolation valves for plant safety.
Rotary valve versatility
With a high range capability of 100-to-1 turndown, and a small footprint, rotary control valves supply a bigger flow coefficient (Cv) than the standard globe style valve.
For instance, Figure 1 reveals a rotary valve utilized in a pulp and paper software that is designed to deal with corrosive and erosive mediums and fiber at the similar time. The geometry and operation of the stem-plug is such that it could possibly function underneath the harshest circumstances, even shearing off material, whereas handling anything flowing via it, from sludge-like materials to sand and small debris. Maintaining performance on this application with a globe valve might be much more troublesome, and should require additional upkeep or compromise in different performance parameters.
The valve in Figure 1 uses an efficient straight-through flow design that enables for a a lot decrease price per Cv than conventional globe-style management valves. Large-shaft diameters machined of high-strength supplies provide the torsional and flexural rigidity required beneath excessive operating pressures.
A globe-style valve would require extra pressure drop for a given flow condition, driving the valve dimension larger, and the difficult circulate circumstances may cause sooner wear and tear of the internals.
Consider a rotary control valve
While many choices work for particular purposes, and globe or angle valves are highly versatile, a rotary management valve can improve on key application challenges that might otherwise lead to oversizing the valve and elevated maintenance. This permits for decreased plant prices and decreased stocking necessities. (See Table 2 for advantages and advantages of rotary plug management valves.)
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