Control Valve Parameters and Definitions of Common Terms: A. Flow Coefficient - Commonly referred to as "Cv" or "Kv" Cv is defined as the full valve opening with 1 lb. Differential pressure across the valve. The flow rate through the valve in one minute at a temperature of 60 ° F represents the GPM in gallons / minute. The Kv value is defined as the flow through the valve in 1 hour at a temperature of 20 ° C with a full valve opening and a pressure differential across the valve of 1 bar and CMPH in meters per hour. Kv = 0.86 Cv. B. Critical Flow Coefficient - FL a. Relative pressure recovery after the fluid has flowed through the valve. b. Low FL = Low Loss: Represents pressure loss in the laminar flow path, such as pressure loss in ball valves and rotating ball valves. c. High FL = High Loss: Indicates the pressure loss in the raw flow conditions, such as pressure loss in the seat ball and gate valves. C. Flow Rate - This is an important parameter because the flow rate affects the life of the valve: high flow rates can cause severe corrosion and wear, and excessive noise. a. Liquid: Typically 15 = 20 ft / s 4.6 - 6 m / s b. Gas or steam: Typically 400 ft / s 122 m / s. Flow a. Flow FT0 b. Flow-Off FTC c. The importance of flow is that it affects stability, leakage and noise. E. Nominal pressure loss - used to select the appropriate valve F. Shutdown pressure - used to select the appropriate actuator G. Seat leakage - according to the provisions of the ANSI standard, is divided into Ⅱ-Ⅵ a. Ⅱ a Rated Cv value of 0.5%, two-seater valve b. Ⅲ a rated Cv value of 0.1% c Ⅳ a rated Cv value of 0.01%, the metal on the single-seat valve most commonly used d. Ⅴ level after grinding the metal valve seat, 5 x 10 4 ml / min e. Ⅵ level a hermetically sealed soft seat valve H. Flow characteristics This feature specifies the flow rate of change with the valve position or the relationship between the valve opening changes curve. I. Noise - There are two types: Hydrodynamic and Gas Noise Hydrodynamic noise is usually caused by the flow of liquid. The gas is most noisy and is caused by gas flow, vapor flow, or liquid vaporization flow. J. Valve Specifications - varies by material and end connection, as specified by the U.S. ANSI K16.34 K. Construction Materials - One of the major factors that should be considered when selecting a regulator. L. End Connections Ways: Optional thread connection, welding, flange or flangeless connection. Usually specified by the user. M. Air Working Method: a. Positive Air Shutoff ATC b. Reaction Air Open ATO N. The test range, also referred to as "elastic limit", refers to pushing the regulating valve to full stroke without load When the required pressure Q. Instrument Signals / Control Signals / Input Signals - The signals sent from the regulator to the regulator are usually 3-15psi or 4-20mA dc P. Gas Sources - It is important to know if the supply pressure is sufficient to meet the job Request. Q. Equalization pressure - refers to the design of the valve stem. Compared with the unbalanced stem design, the balanced design exerts a lower equilibrium pressure on the stem.