User Guide

V46
Issue 9911
© 1999 Johnson Controls Inc.
Catalogue Section 7
Order No. PD
-
V46-E
3
Valve size selection by the use of the
diagram page 4
Q
: The quantity of water (m
3
/h) is indicated on
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
(0,1 up to 4 bar, see scale C).
HPR
: The head pressure rise above the valve
opening point is indicated at the left side of the
lower diagram (max. 4 bar, see scale B).
N
ote
There are two vertical head pressure rise
scales. The left side for range 5/18 bar
valves and the right side for high ranges
5/23 and 10/23 bar valves.
Valve size
: The valve size can be read from the
right side of the upper diagram.
Valve size selection example
:
Q = 6,5 m
3
/h
HPR = 2,7 bar
∆
P = 0,5 bar
a. Draw a horizontal line through the 6,5 m
3
/h
point of scale A (see A).
b. Draw a horizontal line through the 2,7 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 1
1
/
4
" and
1
1
/
2
".
The selected valve is 1
1
/
2
".
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
3
/h.
HPR is 2,5 bar.
The valve size available is
3
/
4
".
What will be the pressure drop?
Solution:
a. Draw a horizontal line through 6 m
3
/h (scale
A) and determine the intersection of this line
with the
3
/
4
" 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 2 and 3 bar
pressure drop curves. Interpolate the point
which gives 2,3 bar.
If this is acceptable the valve can be used.
E.g. Maximum flow.
Valve size is 1"
HPR = 3 bar
Maximum
∆
P = 2 bar
What is maximum Q?
Solution:
a. Draw a horizontal line at 3 bar HPR (scale B)
till intersection with 2 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 9 m
3
/h.
Valve size selection by the use of the
K
v
factors and calculation formulae
For water:
K
v
=
Q
∆
p
∆
∆∆
∆
P
=
Q
K
v
()
2
Q
=
∆
pK
v
•
Q
= quantity of liquid (in m
3
/h)
∆
∆∆
∆
P
= pressure drop across valve (in bar)
K
v
= valve flow coefficient
The K
v
factor is the quantity of 20°C water that
will pass through the valve at one bar pressure
drop and a valve opening which belongs by 3
bar head pressure rise (HPR) above the valve
opening point.
The following K
v
values
can be used:
Valve
size
K
v
value
3/8" 1.8
1/2" 2.7
3/4" 4.5
1" 6.5
11/4" 9
11/2" 10.5
2" 18 (low range)
2" 17 (high range)
21/2" 22 (low range)
21/2" 20(high range)