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They created this standard using reference conditions such as water at a specific temperature flow rate and drop pressure units.
Cv value for control valve. For a specific control valve flow coefficient cv kv is determined experimentally by control valve manufacturers and you can found it in manufacturers technical specifications. Q is the rate of flow expressed in us gallons per minute sg is the specific gravity of the fluid for water 1 δ p is the pressure drop across the valve. Kv 0 864 cv.
40 mm 350 mm 15 mm 20 mm port size 15 mm type s. They express coefficient cv kv as the flow rate of water in g p m. Displaystyle c v q sqrt dfrac text sg delta p where.
Also the cv varies across control valves because each valve lets the flow pass through differently. M3 h for a pressure drop of 1 psi 1 bar across a flow passage flow coefficient. 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.
C v q sg δ p. Diaphragm solenoid valve principle. Cv 1 156 kv.
For example a cv of 150 would then equate to 150 gpm of water at 60 f with a differential pressure of one psi. Flow is proportional to the value of cv. Some vendors have standardized the flow coefficient kv.
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 is applied across the valve. The coefficient of flow or cv value of ball valves is the number of us gallons of water the valve will pass with a differential pressure of 1 psi through the valve at 60 f. Cv value opening degree 0 10 20 30 40 50 60 70 80 90 100 15 mm 20 mm 25 mm type p.
Mathematically the flow coefficient cv or flow capacity rating of valve can be expressed as. Control valve tips and tricks. Table below provides cv values of fully opened ball valves and are approximate values.
Cv 48000 248 33 03 x sqrt 0 86 x 273 240. The valve flow coefficient cv is the number of u s. 0 05 1 0 mpa renge for preset flow rate and working differential pressure.
By definition a cv value of one is the cv required to flow one gallon per minute gpm of water at 60 f with a pressure differential of one psi. The larger the cv the larger the flow at a given pressure differential. Root of δp sg q flow in us gpm.
Valve technician interview questions. The flow coefficient for a control valve which in full open position passes 25 gallons per minute of water with a one pound per square inch pressure drop can be calculated as. Cv flow coefficient of control valve.
The difference of cv relates to the type of the valve and its opening position. What is butterfly check valve. 40 mm 200 mm 25 mm port size 15 mm 237 self control valve constant flow valve pressure setting.
The flow rate for a liquid q cv sq. Cv 25 gpm 1 1 psi 1 2. When you need to do valve sizing for your application you need the cv to select the right valve.
Types of control valves noise. Sg specific gravity of fluid reference against water at 60 f now we discuss about how we get the conversion factor of 1 156 in the formula cv 1 156kv.