What size valve should I use?
So, how do you size a control valve anyway? When sizing a control valve, the rule of thumb is to size it so that it operates somewhere between 20-80% open at maximum required flow rate and whenever possible, not much less than 20% open at the minimum required flow rate.
What is Cv in control valve sizing?
Valve Flow Coefficient (Cv) is the flow capability of a control valve at fully open conditions relative to the pressure drop across the valve. It is defined as the volume of water (GPM in the US) at 60°F that will flow through a fully open valve with a pressure differential of 1 psi across the valve.
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 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.
How do I choose a valve?
The right valve choice means matching the valve’s size to expected flow through the system. Know the chemical compatibility requirements. The valve materials need to be compatible with the gases or liquids flowing through it. Plastic valves usually resist harsh or corrosive chemicals better than metal valves.
How is valve Cv calculation?
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 is Cv calculated?
The formula for the coefficient of variation is: Coefficient of Variation = (Standard Deviation / Mean) * 100. In symbols: CV = (SD/x̄) * 100. Multiplying the coefficient by 100 is an optional step to get a percentage, as opposed to a decimal.
What is rated Cv and calculated Cv?
Thus, rated Cv is Cv attained at full open position. In my opinion, calculated Cv is a Cv value calculated at particular conditions (P1, P2, flow rate, specific gravity etc.). Conditions can give you min Cv, max Cv or a Cv value somewhere between those two. So when selecting a valve min and max Cv are of importance.