Cv factor for valves

Gallons per minute that will pass through a valve with a pressure drop of (1) psi. The full closure curve of a ball valve is then the above graph multiplied by the valve’s flow coefficient or factor. Size 150 300 600 900 1500 2500 2 42 42 42 45 38 25 2.5 67 67 67 / / / 3 100 100 100 90 95 65 4 185 185 185 170 170 1005 6 440 440 440 400 395 265 The equations below can be used to determine: The diagram below is a nice tool to simplify the conversion between the different coefficients. In a situation of special travel and differential pressure 1 lbf/in2. It can be assumed that the tests are done with water (unless otherwise noted), using a specific gravity of 1.0, 1.2 centistoke viscosity, and a standard temperature of 60 degrees fahrenheit. .048 substituting in the formula, we have: They provide a means of comparing the flow capacities of different brands of valves; “cv” is a term constantly used in selecting valves. Liquid critical pressure ratio factor, f f the liquid critical pressure. Formulas and cv factors cv factors: Sometimes, the cv value is given instead of the kv value. For example, a valve with cv of 4.00 will pass 4 times as much flow at the same pressure difference as shown in the chart. Cv & kv relation :

Cv vs angle closure curve values table. A valve cv can be described as the number of gallons per minute (gpm) at 60 o f (15.5 o c) that will pass through a valve with an associated pressure drop of 1 psi. Contrast this with the resistance factor k (the one used for pipe fittings like bends etc). The flow factor is commonly used outside u.s. The valve flow coefficient, cv, is the number of u.s. The complete definition also says that the flow medium must have a specific gravity of 1000 kg/m 3 and a kinematic viscosity of 10 −6 m 2 /s. It allows you to calculate the flow or c v (flow coefficient) to make the relationship visible between the pressure drop (the difference in pressure between two points in a network transporting a liquid or gas) and the flow rate. 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. With the flow coefficients capacities of valves at different sizes, types and manufacturers can be compared. Compression factor at 80 psi, from table 2. Cv factor can be calculated as following formula. A fitting with a high k value passes fluid less easily than one with a low k value. However, there is a problem with using this equation in pneumatic applications. Butterfly valve cv values vary with the disc angle and valve size. Throttling characteristics are shown in the same manner with cv’s at various openings.

It is defined as the flow rate in us gallons per minute [gpm] of water at a temperature of 60º fahrenheit with a pressure drop across the valve of 1 psi. Gallons per minute of water at 60°f that will flow through a control valve at a specified opening when a pressure differential of 1psi. Control valve cv refers to the flow coefficient of the valve. This is our valve c v calculator. A simplified version of the definition is: For the same pressure conditions, if we increase the valve opening to create cv = 10, it will pass 10 us gpm provided 1 psi pressure drop across the valve (remains same). This calculator can be used to help select a valve with enough flow capacity for a given application. The definition of cv is the # of gallons of water that will flow through the valve with a 1 psi pressure differential when the valve is open. Valves are tested by running water through it before publishing the cv value. C v & flow calculator. It applies to the factor of the head drop (δh) or pressure drop (δp) over a valve with the flow rate q. 8.30 x 12 x 6.4 x.048 cv = 1 x 28.8 = 1.06 any valve, therefore, which has a cv of at least 1.06, will extend our cylinder the specified distance in the required time. The use of this flow coefficient (c v) calculator leads to a standard calculation to compare valve capacities. A cv of 1 then, means that one gallon of water passed through a valve in 1 minute. And if cv factor is same, flow rate is big so that differential pressure is big.

Because air is compressible, cv must have additional factors built into the equations to compensate for that compressibility. The following formula is often used using a fluid’s specific gravity (g) where the relationship to water density is already considered. Q = cv x δp g likewise, cv for particular flow characteristics can be determined from The process of valve size selection, the same formula is used determine the valve cv necessary for a required flow rate and desired pressure drop. Flow coefficients cv values the flow coefficiency (cv) of a valve is the rate of gallons per minute of water at 60° f through a fully opened valve at a pressure drop of 1 psi across the valve. In the chart below, we show the approximate cv value of butterfly valves ranging from 2 to 24 and at various disc angles. Cv is based on the volume flow rate of water at 60°f through a device within one minute at a 1 psi differential. Scfm air flow through a valve orifice having a cv factor of 1.00 Cv is the amount of flow in gallons per minute through a valve which results in a 1 psi pressure drop. The flow coefficients are in general determined experimentally and express the. And they allow the designer to predict with reasonable accuracy just how a newly designed system will perform. Cv is the flow coefficient in imperial units. Cv value is an imperial measure of flow in us gallons per minute of water at 60° fahrenheit with a pressure drop of 1 psi across the valve. If differential pressure is same, flow rate is big so that cv factor is big. 6.4 “a” constant for 80 psi, from table 2.

Kv = 0.864 cv at a particular percentage of opening of valve giving cv = 1 will pass 1us gpm ( at 60 °f) and a pressure differential of 1 psi upstream and downstream across the valve. A valve with a high cv passes fluid more easily than one with a low cv. Full port valves will have a higher cv than reduced port valves. Cv flow coefficient ratings have several advantages: Converting between flow coefficient c v and flow. Thus they tend to choke (or cavitate) at smaller pressure drops than globe valves. The required cv range for this application than is.0141 to.0703. The tables below list the full cv vs angle closure and opening curves for various valve diameters: On valves or orifices with other cv factors, the flow capacity will be directly proportional to the cv rating. The cv value of.0141 is reached at approximately turn 2.3, while the cv value of.0703 is reached at approximately turn 14.6. The cv factor is the number of u.s. This is used as a guide and is not a linear progression. The flow of water through a valve at 60°f in us gallons/minute (gpm) at a pressure drop of 1lb/in². They simplify the job of selecting an adequately sized valve without wasteful oversizing; The cv factor is a standard used by all valve manufacturers.

The k v factor of a valve indicates the water flow in m 3 /h, at a pressure drop across the valve of 1 kgf /cm 2 when the valve is completely open. The definition of cv is the number of gpm (gallons per minute ) that will pass through the control valve with a pressure drop of 1psi. The valve flow coefficient (c v) is a convenient way to represent flow capacity of a valve across a range of fluids and process parameters.the c v calculator will calculate either c v or flow using the supplied additional parameters of fluid, inlet and outlet. The conversion factor between two coefficients is indicated with arrows. Q = cv x δp x 62.4 d the formula above utilizes a conversion factor of 62.4 which is the density of water in lbs/ft³. The below cv values are used to give an indication of flow rates for ball valves. The valve flow coefficient cv or its metric equivalent kv has been adopted universally as a comparative value for measuring the capacity of control valves. The cv rating for each valve is listed in the tables found in the valve catalog. Cv factor is using generally, it is expressed factor for fluid 60°f that flow into valve by us gal/min.

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