The material follows the sequential order of the typical Valtek Valves quote sheet. Valtek Introduction Valtek Mark One Mark One globe-style control valves feature a standard cast carbon steel or stainless steel globe body, top entry trim with a characterized plug contour, high thrust double-acting piston actuator, four-way positioner, and fail-safe return spring. Body styles include standard globe, globe with expanded outlets Mark One-Xangle and three-way configurations.
The successful operation of process plant and systems involves the highest level of measurement and control performance. Control valves therefore perform a key function in this process. The performance of control valves can have a dramatic effect on plant operating efficiency, overall profitability and asset life cycle costs.
A correctly sized control valve can provide significant quantifiable savings as well as increase process availability, reduce process variability and reduce maintenance costs.
Correctly sized control valves also last longer in comparison to unmatched or incorrectly sized valves. Careful consideration should therefore be given to the correct sizing of system control valves.
The Importance of Sizing Control valve sizing procedures are based on accepted mathematical methods such as those detailed in ISA These methods can be used to develop accurate valve sizes however, during the course of plant design, control valves are often sized based on a future maximum design process load plus a safety factor.
This can result in the specification, procurement and maintenance of a larger valve than necessary thus producing imprecise control, poor production performance in addition to the operational issues discussed above. When sizing a control valve, the most common approach is to calculate the flow coefficient, Cv which is a measure of the capacity of the valve body and trim.
The flow coefficient is discussed in further detail below. Most valve manufacturers publish Cv data in product catalogues for various valve styles. Table 1 provides an example of an equal percentage valve curve characteristic as published by Crane Engineering. Equal Percentage Characteristic Curve Co-ordinates The performance curve for the tabulated co-ordinates is shown in Figure 1.
The tabulated coordinates for this performance curve have been defined in the FluidFlow control valve database. The control valve performance curve is automatically generated by the software and can be viewed in Figure 2.
As shown in Figure 3, the calculated FluidFlow result matches exactly with the Crane Engineering example. If the Cv for a control valve is not calculated correctly or accurately, the resultant selected valve will experience diminished performance.
Undersized valves exhibit a higher pressure drop across the valve to maintain adequate flow and exhibit limited flow capacity. Furthermore, since the restriction in the valve can cause a build-up of upstream pressure, higher back pressures created before the valve can lead to damage in upstream pumps or other upstream equipment.
Although relatively uncommon, an undersized control valve generally cannot deliver sufficient flow rates under maximum load conditions. If the Cv calculated is too high for the system requirements, the result is a larger oversized control valve is usually selected.
In addition to the more obvious issues with an oversized valve such as a larger cost, weight and size, when in throttling service, significant control instability can occur. Usually the closure element, such as the valve plug or disk, is positioned just off the valve seat which leads to higher pressure drops across the valve and higher fluid velocities which can cause cavitation, flashing or erosion of the valve trim elements.
Cavitation can occur in liquid systems when high velocity reduces the static pressure inside the valve to below the pressure level at which the liquid stats to boil and produce vapor bubbles.
These vapor bubbles collapse whenever the downstream pressure is higher than the vapor pressure causing high pressure waves.Valve Sizing Technical Bulletin Scope Valve size often is described by the nominal size of the end connections, but a more important measure is the flow that the valve can provide.
And determining flow through a valve can be simple. This technical bulletin shows how flow can be estimated. Passing Through a Valve Control Valve Sizing Sizing & Selection 3. ∆P/G f Volumetric Flow Rate q max C V = q / ∆P/G f ∆P ch Liquid Pressure Recovery Factor, F L The liquid pressure recovery factor, F L, predicts the amount of pressure recovery that will occur between.
© Resideo Technologies, Inc. The Honeywell Home trademark is used under license from Honeywell International Inc. When control valve professionals talk about "control valve sizing," they really mean the entire process of selecting the valve that will do the best job of controlling the process.
Selecting the right size valve is an important part of the process, but there are other equally important considerations as well. Valve Sizing Calculator. Please use this form to help select the correct valve for your application.
Use the selection as a guide only. Hass Manufacturing Company accepts no responsibility for the acceptability or fitness of use.
Welcome to the Emerson Automation Solutions Sizing website. This site is devoted to providing our customers the most up to date information about the valve sizing and selection software programs for Emerson Automation Solutions including our latest version of relief valve sizing software, PRV 2 SIZE.