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V48
Issue 09/01/2003
Valve size selection by the use of the
diagrams pages 4 and 5
Q: The quantity of water (m
the left side of the upper diagram
(= scale A).
∆ P: The curves for the pressure drop across
the valve are indicated in the lower diagram
(0,25 up to 1 bar, see scale C).
HPR: The head pressure rise above the valve
opening point is indicated in the lower part of the
diagrams on pages 4 and 5 (see scale B).
Note
On page 4 there are two vertical head
pressure rise scales. The left side for low
range (1.5/7.5 bar) valves and the right
side for high range (4/16 bar) valves.
On page 5 for range 4/20 and 6/20 bar
valves.
Valve size:
The valve size can be read from the right side of
the upper diagram.
Valve size selection example (see page 4):
Q
= 5.1 m
HPR
= 3.2 bar
∆ P
= 0.5 bar
Refrigerant = R22
Valve range = 4/16 bar
a. Draw a horizontal line through the 5.1 m
point of scale A (see A).
b. Draw a horizontal line through the 3.2 bar of
scale B (see B). The intersection of this
horizontal line with the delta P curve of 0.5
bar is used to draw a vertical line from this
intersection point up to the horizontal line in
scale A (see C).
c. The intersection point of this vertical line with
the horizontal line in scale A indicates the
valve size. If the point falls on a size curve,
this is the valve size needed. If it is between
two sizes always take the largest valve size.
In this example it is between size
The selected valve is 1".
Of course the same diagram can be used to
read the pressure drop across a valve or to find
the maximum capacity of a valve.
E.g. Pressure drop.
Q needed is 6 m
/h.
3
HPR is 2.5 bar.
The valve size available is 1".
What will be the pressure drop?
© 2002 Johnson Controls Inc.
Code No. PD-V48-E
3
/h) is indicated on
/h
3
/h
3
3
and 1".
/
"
4
Solution:
a. Draw a horizontal line through 6 m
A) and determine the intersection of this line
with the 1" valve curve.
b. Draw a vertical line from this intersection
point to the 2.5 bar HPR line.
c. The found part is between the 0.5 and 0.75
bar pressure drop curves. Interpolate the
point which gives 0.7 bar.
If this is acceptable the valve can be used.
E.g. Maximum flow.
Valve size is 1"
HPR = 3 bar
Maximum ∆ P = 0.25 bar
What is maximum Q?
Solution:
a. Draw a horizontal line at 3 bar HPR (scale B)
till intersection with 0.25 bar delta P curve.
b. Draw a vertical line from this intersection
point to the 1" valve curve.
c. Draw from this point a horizontal line to the
water flow scale A.
You find 4.0 m
/h
3
Valve size selection by the use of the
K v factors and calculation formulae
For water:
The following K v values
can be used:
Q
K v =
Valve
∆p
size
2
1/2"
Q
(
)
∆ P =
3/4"
K v
1"
11/4"
K v •
∆p
Q =
11/2"
Q
= quantity of liquid (in m
∆ P = pressure drop across valve (in bar)
K v
= valve flow coefficient
The Kv factor is the quantity of 20°C water that
will pass through the valve at one bar pressure
drop (port 1 to port 2) and a valve opening which
belongs by 2.2 bar (for low range valves) or 3
bar (for high range valves) head pressure rise
(HPR) above the valve opening point.
3
/h (scale
3
K v value
2.3
4.7
8.0
10.2
16.5
3
/h)
Catalogue Section 7
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