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The use of the flow coefficient offers a standard method of comparing valve capacities and sizing valves for specific applications that is widely accepted by industry. The general definition of the flow coefficient can be expanded into equations modeling the flow of liquids, gases and steam using the
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104:
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For air flow at room temperature, when the outlet pressure is less than 1/2 the absolute inlet pressure, the flow becomes quite simple (although it reaches sonic velocity internally). With
179:= 1.0 and 200 psia inlet pressure, the flow is 100 standard cubic feet per minute (scfm). The flow is proportional to the absolute inlet pressure, so the flow in scfm would equal the
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is the volume (in US gallons) of water at 60 °F (16 °C) that will flow per minute through a valve with a pressure drop of 1 psi (6.9 kPa) across the valve.
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flow coefficient if the inlet pressure were reduced to 2 psia and the outlet were connected to a vacuum with less than 1 psi absolute pressure (1.0 scfm when
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for the same assembly can be used with a more complex equation. Absolute pressures (psia) must be used for gas rather than simply differential pressure.
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factor or value as it is also called is defined in VDI/VDE Richtlinien No. 2173. A simplified version of the definition is: The k
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when the valve is completely open. The complete definition also says that the flow medium must have a density of
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factor of a valve indicates "The water flow in m/h, at a pressure drop across the valve of
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Fluidic characteristic quantities of control valves and their determination
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Strömungstechnische Kenngrößen von
Stellventilen und deren Bestimmung
401:
266:{\displaystyle K_{\text{v}}=Q{\sqrt {\frac {\text{SG}}{\Delta P}}},}
99:{\displaystyle C_{\text{v}}=Q{\sqrt {\frac {\text{SG}}{\Delta P}}},}
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is the differential pressure across the device (expressed in bar).
23:
of a device is a relative measure of its efficiency at allowing
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is the pressure drop across the valve (expressed in psi).
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is the rate of flow (expressed in US gallons per minute),
51:(or flow-capacity rating of valve) can be expressed as
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Measure of a device's efficiency at allowing fluid flow
374:{\displaystyle C_{\text{v}}=1.156\cdot K_{\text{v}}.}
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27:flow. It describes the relationship between the
35:valve or other assembly and the corresponding
158:For gas flow in a pneumatic system the
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287:is the flow factor (expressed in m/h),
218:) is calculated using metric units:
42:Mathematically the flow coefficient
293:is the flowrate (expressed in m/h),
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300:of the fluid (for water = 1),
135:In more practical terms, the
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197:= 1.0, 2 psia input).
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486:: what, why, how, whence?"
513:"Control Valve Sizing".
321:can be calculated from
566:. September 2007. 2173
516:Control Valve Handbook
432:. Technical Bulletin.
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205:The metric equivalent
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589:Discharge coefficient
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153:discharge coefficient
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491:. Technical paper.
330:using the equation
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526:. September 2019
524:Emerson Electric
522:(5th ed.).
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480:Boysen, Herman.
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400:and a kinematic
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298:specific gravity
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137:flow coefficient
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120:specific gravity
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21:flow coefficient
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604:Fluid dynamics
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427:"Valve Sizing"
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398:1000 kg/m
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408:, e.g. water.
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394:1 kgf/cm
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29:pressure drop
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568:. Retrieved
558:(Standard).
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528:. Retrieved
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496:. Retrieved
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463:. Retrieved
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530:26 February
459:Calculator"
406:10 m/s
207:flow factor
201:Flow factor
461:. Generant
413:References
296:SG is the
118:SG is the
31:across an
402:viscosity
356:⋅
251:Δ
84:Δ
37:flow rate
598:Category
583:See also
570:17 April
498:21 April
465:21 April
439:21 April
434:Swagelok
493:Danfoss
33:orifice
554:]
275:where
108:where
556:(PDF)
550:[
520:(PDF)
489:(PDF)
430:(PDF)
384:The k
353:1.156
25:fluid
572:2020
532:2022
500:2020
467:2020
441:2020
19:The
564:VDE
560:VDI
404:of
600::
562:,
482:"k
455:"C
247:SG
155:.
80:SG
39:.
574:.
534:.
502:.
484:V
469:.
457:v
443:.
390:v
386:v
369:.
364:v
360:K
350:=
345:v
341:C
327:v
324:C
318:v
315:K
306:P
304:∆
291:Q
284:v
281:K
261:,
254:P
241:Q
238:=
233:v
229:K
215:v
212:K
209:(
194:v
191:C
185:v
182:C
176:v
173:C
164:v
161:C
144:v
141:C
128:P
126:Δ
113:Q
94:,
87:P
74:Q
71:=
66:v
62:C
48:v
45:C
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