Cv Factor For Valves
However, there is a problem with using this equation in pneumatic applications. Cv is based on the volume flow rate of water at 60°f through a device within one minute at a 1 psi differential.
Full port valves will have a higher cv than reduced port valves.
Cv factor for valves. The cv rating for each valve is listed in the tables found in the valve catalog. In a situation of special travel and differential pressure 1 lbf/in2. 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.
Contrast this with the resistance factor k (the one used for pipe fittings like bends etc). It applies to the factor of the head drop (δh) or pressure drop (δp) over a valve with the flow rate q. Thus they tend to choke (or cavitate) at smaller pressure drops than globe valves.
.048 substituting in the formula, we have: This is used as a guide and is not a linear progression. Gallons per minute that will pass through a valve with a pressure drop of (1) psi.
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. Kv = 0.865 · cv cv = 1,156 · kv (equivalence between flow coefficients kv and cv) “cv” is a term constantly used in selecting valves.
Cv flow coefficient ratings have several advantages: The cv factor is a standard used by all valve manufacturers. Cv & kv relation :
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. With the flow coefficients capacities of valves at different sizes, types and manufacturers can be compared.
On valves or orifices with other cv factors, the flow capacity will be directly proportional to the cv rating. 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. 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.
A fitting with a high k value passes fluid less easily than one with a low k value. Cv vs angle closure curve values table. In the chart below, we show the approximate cv value of butterfly valves ranging from 2 to 24 and at various disc angles.
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. C v & flow calculator. Control valve cv refers to the flow coefficient of the valve.
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. This calculator can be used to help select a valve with enough flow capacity for a given application. 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.
A cv of 1 then, means that one gallon of water passed through a valve in 1 minute. The flow of water through a valve at 60°f in us gallons/minute (gpm) at a pressure drop of 1lb/in². The valve flow coefficient, cv, is the number of u.s.
A valve with a high cv passes fluid more easily than one with a low cv. Q = cv x δp g likewise, cv for particular flow characteristics can be determined from The flow factor is commonly used outside u.s.
Formulas and cv factors cv factors: 6.4 “a” constant for 80 psi, from table 2. The use of this flow coefficient (c v) calculator leads to a standard calculation to compare valve capacities.
The tables below list the full cv vs angle closure and opening curves for various valve diameters: Throttling characteristics are shown in the same manner with cv’s at various openings. The cv factor is the number of u.s.
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 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 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 equations below can be used to determine: Scfm air flow through a valve orifice having a cv factor of 1.00 C v calculator for valve sizing.
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. Converting between flow coefficient c v and flow. This is our valve c v calculator.
And if cv factor is same, flow rate is big so that differential pressure is big. 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). The conversion factor between two coefficients is indicated with arrows.
The below cv values are used to give an indication of flow rates for ball valves. Cv is the flow coefficient in imperial units. They simplify the job of selecting an adequately sized valve without wasteful oversizing;
Compression factor at 80 psi, from table 2. 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. Cv factor is using generally, it is expressed factor for fluid 60°f that flow into valve by us gal/min.
Because air is compressible, cv must have additional factors built into the equations to compensate for that compressibility. Flow coefficient, cv, and flow factor, kv, are values used to specify the hydraulic capacity of a control valve. A simplified version of the definition is:
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 Cv factor can be calculated as following formula. Liquid critical pressure ratio factor, f f the liquid critical pressure.
Flow coefficient is an imperial measurement and is defined as: Sometimes, the cv value is given instead of the kv value. And they allow the designer to predict with reasonable accuracy just how a newly designed system will perform.
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. 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. They provide a means of comparing the flow capacities of different brands of valves;
The required cv range for this application than is.0141 to.0703. The full closure curve of a ball valve is then the above graph multiplied by the valve’s flow coefficient or factor. 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.
If differential pressure is same, flow rate is big so that cv factor is big. The diagram below is a nice tool to simplify the conversion between the different coefficients. 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.
The following formula is often used using a fluid’s specific gravity (g) where the relationship to water density is already considered. Butterfly valve cv values vary with the disc angle and valve size. 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.
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. 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. 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.
Valves are tested by running water through it before publishing the cv value.
