How do you calculate control valve size?
Control Valve Sizing – FluidFlow
- Control Valve Sizing.
- 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 = Q/N1 * √ (ρ1/ρ0) / (∆P)
- ρ1/ρ0 is the relative density.
- Fluid Density: 965.4 kg/m3.
What is control valve sizing?
For sizing a control valve we are interested in knowing how much flow we can get through the valve for any given opening of the valve and for any given pressure differential. The relationship between pressure drop and flow rate through a valve is conveniently expressed by a flow coefficient (Cv).
What is CG in control valve sizing?
C1 = Cg/Cv. G = gas specific gravity (air = 1.0) P1 = inlet pressure, psia. P2 = outlet pressure, psia. ΔP = pressure drop P1 – P2, psi.
What is xT in control valve sizing?
For compressible fluids, a terminal pressure drop ratio, xT, similarly describes the choked pressure drop for a specific valve. When sizing a control valve, the smaller of the actual pressure drop or the choked pressure drop is always used to determine the correct Cv.
How do you calculate Cv for control valve?
Inlet Pressure 32 kgf / cm2 Convert to absolute pressure = 33.03 kgf / cm2 (A). Outlet Pressure 15 kgf / cm2 convert to absolute pressure = 16.03 kgf / cm2 (A). Because the fluid is a gas and ΔP ≥ P1 / 2 so we will use the formula. Cv = (48000 / (248 × 33.03)) x sqrt (0.86 x (273 240)).
How do I choose a control valve?
When choosing a control valve for a process, there are many things that must be considered, including the valve’s flow characteristic, its size, noise, the potential for cavitation or flashing damage, body and trim materials, actuator size and type, and its dynamic response to changes in the control signal.
What is CG valve?
They express flow coefficient Cg or Kg as the flow rate of water in g.p.m. [m3/h] for a pressure drop of 1 psi [1 bar] across a flow passage [flow coefficient: Cg-imperial, Kg-metric]. You can calculate the gas control valve capacity for given upstream and downstream pressure and known flow coefficient Cg or Kg.
What is rated valve capacity?
Rated valve capacity is the capacity based on the published Cv values for a given valve. Standards do specify leakage rate as a percentage of rated Valve capacity like 0.01 % and etc.. That means the leak across the valve in its fully closed condition at the test pressure should not exceed this limit.
What is choked flow ratio?
The ratios were obtained using the criterion that choked flow occurs when the ratio of the absolute upstream pressure to the absolute downstream pressure is equal to or greater than , where. is the specific heat ratio of the gas.
What is valve choked flow?
What is Choked Flow in a Gas Control Valve? Choked flow is the point at which decreasing downstream pressure will not increase the flow through a valve. This typically happens in high differential applications in a high pressure control valve in gas back pressure or pressure reducing service.
How do you calculate control valve flow?
The volume flow rate for liquids can be calculated by multiplying the fluid velocity times the flow area. Thus, Cv is numerically equal to the number of U.S. gallons of water at 60°F that will flow through the valve in one minute when the pressure differential across the valve is one pound per square inch.
How to size control valves?
• The differential pressure across the valve. The control valve can be sized to operate at a certain differential pressure by using a graph relating flowrate, pressure drop, and valve flow coefficients. Alternatively, the flow coefficient may be calculated using a formula.
How to size a gas control valve?
Specify the required design flow rate
What control valve CV means and how to calculate it?
Cv by definition is the number of gallons per minute (GPM) a valve will flow with a 1 psi pressure drop across the valve. For example a valve with a Cv of 10 will flow 10 GPM with a 1 psi pressure drop. The formula used to select the valve Cv with the specified differential pressure is: Cv=GPM/((SQ RT(∆P)).
What is control valve sizeing?
Physical details (pipe size,pressure class,trim type)