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Z1

Z1

.3

CALCULATING THE FLOW RATE OF A VALVE USING FLOW COEFFICIENT k

V

CALCULATING THE FLOW RATE OF A VALVE USING FLOW COEFFICIENTS C AND B

CALCULATING THE FLOW RATE OF A VALVE USING FLOW COEFFICIENTS C

V

Coefficient k

V

gives approximate values when used for compressed air.

The flow rate Q

N

at a normal volume through a valve is:

Subsonic flow: P

2

.

Supersonic flow: P

2

,

where

Q

N

= flow rate at a normal volume [Nl/min]

Q

N

* = critical flow rate at a normal volume [Nl/min]

k

V

= hydraulic coefficient in

P

1

= absolute upstream pressure [bar]

P

2

= absolute downstream pressure [bar]

∆P = difference in pressure P

1

– P

2

[bar]

t

= input air temperature [°C]

P

1

2

P

1

2

The flow rate Q

N

at a normal volume through a valve is:

Subsonic flow: P2

.

b · P

1

Supersonic flow: P2

,

b · P

1

where

Q

N

= flow rate at a normal volume [Nl/min]

Q

N

* = critical flow rate at a normal volume [Nl/min]

C = conductance in [Nl/min · bar]

P

1

= absolute upstream pressure [bar]

P

2

= absolute downstream pressure [bar]

r

= upstream pressure : downstream pressure ratio P

2

/P

1

b = critical pressure ratio b = P

2

* /P

1

t

= input air temperature [°C]

The flow rate Q

N

at a normal volume through a valve is:

Subsonic flow: P

2

.

0.528 · P

1

Supersonic flow: P

2

,

0.528 · P

1

where

Q

N

= flow rate at a normal volume [Nl/min]

Q

N

* = critical flow rate at a normal volume [Nl/min]

C

V

= coefficient of flow [US · GPM / p.s.i.]

P

1

= absolute upstream pressure [bar]

P

2

= absolute downstream pressure [bar]

t

= input air temperature [°C]

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