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Valve Sizing

Check-All provides two methods for valve sizing: Flow Curves and Cv Factor, which help determine the correct valve size based on flow requirements. The Cv Factor represents the flow coefficient, indicating the relationship between flow rate and pressure drop, with higher Cv values allowing for greater flow. The document also includes formulae for calculating flow rates for liquids, gases, and saturated steam based on Cv and pressure drop.

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Kamel Salah
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9 views1 page

Valve Sizing

Check-All provides two methods for valve sizing: Flow Curves and Cv Factor, which help determine the correct valve size based on flow requirements. The Cv Factor represents the flow coefficient, indicating the relationship between flow rate and pressure drop, with higher Cv values allowing for greater flow. The document also includes formulae for calculating flow rates for liquids, gases, and saturated steam based on Cv and pressure drop.

Uploaded by

Kamel Salah
Copyright
© © All Rights Reserved
We take content rights seriously. If you suspect this is your content, claim it here.
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Download as PDF, TXT or read online on Scribd
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TECHNICAL D ATA

Valve Sizing – Check-All furnishes two methods to aid the customer in the selection of the correct
valve size to meet their flow requirements; Flow Curves and Cv Factor.

Flow Curves show the relationship between the rate of flow (water, gpm) and the pressure drop
across the valve produced by that flow.

Cv Factor is a valve flow coefficient which mathematically gives the relationship between the rate of
flow and the pressure drop.

Definition: Cv is defined as the quantity of 60° F. water, in


gallons per minute, which will pass through a specific valve
at maximum lift, at one (1) psi pressure drop.

It is experimentally determined by dividing the water flow through the valve by the square root of
the pressure drop produced by that flow. Conversely, given the Cv, the water flow through the valve
at any given pressure drop may be calculated by multiplying the Cv by the square root of the
pressure drop. Therefore, for a given pressure drop, the higher the Cv, the higher the rate of flow.

For liquids other than water, for gases and for saturated steam, the formulae given below will show
the relationship between the Cv (as obtained from water flow tests) and the flow of these fluids.
FLOW FORMULAE
(Non-Choked Turbulent Flow Only)
I. LIQUIDS
2
dP V V
V = Cv dP = G Cv =
G Cv
dP
Where V = Liquid flow (gpm) G
dP = Pressure drop (psi)
G = Sp. Gravity of liquid (water = 1.0)
Cv = Valve coefficient

II. GASSES
2
dP P1 + P2 Q
Q = 1360 Cv dP = P – 2 Q Cv =
GT 2 1 P1 – 2GT
1360 Cv dP P1 + P2
1360 GT 2
Where Q = Gas flow (scfh)
dP = Pressure drop (psi)1
T = Absolute temp of flowing medium (degrees Rankin)
P1 = Inlet pressure (psia)
P2 = Outlet pressure (psia)
Cv = Valve coefficient
G = Sp. Gravity of gas (air = 1.0)

III. SATURATED STEAM


2
P1 + P2 W W
W = 3 Cv dP dP = P – 2
P1 – 2 Cv =
1
2 3 Cv P1 + P2
3 dP
Where W = Saturated steam flow (lbs. per hour) 2
dP = Press drop (psi)1
P1 = Inlet pressure (psia)
1 – For calculation purposes, dP should
P2 = Outlet pressure (psia)
Cv = Valve coefficient never exceed 1/2 the inlet pressure, P1.

2006

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