Sizing procedure
Flow velocity is recommended to be kept within 3 to 6 feet per second
when calculating the correct pressure reducing valve size. This will
prevent noise in the pipes and rapid wear of fixtures. The valve will
accurately control pressure down to a velocity of 1 fps.
The correct size of the pressure reducing valve is taken from graph 1
on the basis of the design flow rate taking into account an ideal flow
velocity in the valve body of between 3 and 6 f/s (blue band).
Example:
For 8 gpm, select the 3/4” size valve (see arrow on graph 1).
The pressure drop is taken from graph 2 also on the basis of where the
design flow rate intersects the curve for the valve size already selected
(the downstream pressure falls by an amount equal to the pressure
drop, with respect to the set pressure at no flow condition).
Example:
For 8 gpm the ∆p = 10 psi
(see arrow on graph 2).
Design Flow Rate
Size
½"
¾"
gpm
3 to 5.6
5.6 to 10
l/min
11 to 21
21 to 38
∆
p (bar)
0,5
1
0,2
0,1
1,5
0,3
0,4
0,6
0,8
1,2
0,9
0,7
∆
p (m w.g.)
5
10
2
1
15
3
4
6
8
12
9
7
5351
1/2"
3/4"
5350
1/2"
3/4"
1"
1"
1 1/4"
1 1/2"
2"
0.45
5
V (m/s)
0.1
4
3
0.3
1 1/4"
(535074/5)
1/2”
3/4”
1
2
5
0,2
10
20
20
50
100
Flow rate
(l/min) (m
3
/h)
200
5
10
1.5
V (f/s)
0.3
15
10
1
8
20
90
Flow rate
(/s)
(gpm)
30
40
10
5
2
1
0.9
5
50
60
70
1
2
0.5
0.2
0.1
0.05
3
4
6
1.5
0.3
0.4
2.5
80
3
4
0.15
0.5
2
0.6
3
0.9
6
1.8
5
4
1.2
Graph 1 (Flow velocity)
0
0
5
10
15
20
25
20
25
15
10
5
0
0
2
4
6
8
10
12
14
16
18
20
170
160
(kPa)
(psi)
(psi)
140
120
Flow
(l/min)
(
gpm)
5
10
15
20
30
25
35
40
45
50
55
60
65
70
75
100
80
80
60
40
20
0
Graph 2
Pr
essur
e dr
op
Reference: Upstream pressure = 115 psi (800 kPa)
Downstream pressure = 45 psi (310 kPa)
1/2”
3/4”
