Agricultural Valves – Low Pressure Operation
The following charts explain the pressure and flow rate relationship for operation of Rain
Bird Agricultural Valves at low pressure. All data shown are for valves with low pressure
diaphragms and valve springs. Standard diaphragms and springs are for operation
between 50 and 230 PSI and should not be used in low pressure applications.
Each graph also shows the maximum flow rate through the valve due to the limits of water
velocity.
Open-Close Function
1” Valve
60
Each line shows the flow rate and pressure
loss for a given inlet pressure.
Maximum flow rate for this valve is 53 GPM
Flow (GPM)
50
The example with a 1 inch valve shows that
when the inlet pressure is 20 PSI, there is a
5 PSI pressure loss at 29 GPM flow rate.
40
30
20
30 PSI Inlet, Maximum 53 GPM
10
20 PSI Inlet, Maximum 36 GPM
15 PSI Inlet, Maximum 24 GPM
10 PSI Inlet, Maximum 16 GPM
0
0
2
4
6
8
10
12
14
16
Pressure Loss (PSI)
4” Valve
900
The point where each inlet pressure line
begins to straighten and go horizontal is the
maximum flow rate at the given inlet
pressure.
Maximum flow rate for this valve is 838 GPM
800
Flow (GPM)
700
600
The example with a 4 inch valve shows that
the maximum flow rate is 398 GPM with an
inlet pressure of 15 PSI.
500
400
300
30 PSI Inlet, Maximum 838 GPM
200
20 PSI Inlet, Maximum 593 GPM
15 PSI Inlet, Maximum 398 GPM
100
10 PSI Inlet, Maximum 214 GPM
0
0
2
4
6
8
10
Pressure Loss (PSI)
12
14
16
If a higher flow rate is needed, the options
are:
• Increase the upstream pressure, or
• Use a larger valve
Operation with a pressure reducing pilot
M a x im u m Flo w ( G P M )
2” Valve
Each line represents
downstream pressure.
300
250
6 PSI Downstream
100
8 PSI Downstream
50
10 PSI Downstream
0
10
20
30
different
With the pilot set at a certain
downstream pressure, the valve will
have stable operation when the
upstream pressure and flow rate are at
any point below the line for the set
downstream pressure.
200
150
a
40
Upstream Pressure (PSI)
For example, if the pilot is set to
maintain a 6 PSI downstream pressure,
the upstream pressure and flow rate
could be any value in the shaded area.
300
In this example for a 2 inch valve, the
point
shows that the upstream
pressure is 30 PSI and the flow rate is
150 GPM.
250
200
150
This valve can operate accurately if the
downstream pressure is set at either 10
or 8 PSI. However, it will not be stable at
6 PSI downstream pressure, because the
upstream pressure is more than 4 times
the downstream pressure.
6 PSI Downstream
8 PSI Downstream
10 PSI Downstream
100
50
0
10
20
30
40
Upstream Pressure (PSI)
M a x im u m Flo w ( G P M )
M a x im u m Flo w ( G P M )
2” Valve
300
2” Valve
The point identified with a
shows
stable operating conditions for 8 and 10
PSI downstream pressure. This point is
located below the 10 and 8 PSI
downstream pressure line. However at the
same flow and upstream pressure, the
valve’s operation would not be stable with
the downstream pressure set at 6 PSI.
250
200
150
6 PSI Downstream
8 PSI Downstream
10 PSI Downstream
100
50
0
10
20
30
Upstream Pressure (PSI)
40
If the upstream pressure and flow rate fall
on a point above the set downstream
pressure line, the options are:
• Increase the upstream pressure
• Use a larger valve
Open-Close Operation
1" w/LP Diaphragm and Spring
Pressure Loss Vs. Flow
60
Maximum Flow Rate for this valve is 53 GPM
Flow (GPM)
50
40
30
20
30 PSI Inlet, Maximum 53 GPM
20 PSI Inlet, Maximum 36 GPM
15 PSI Inlet, Maximum 24 GPM
10 PSI Inlet, Maximum 16 GPM
10
0
0
2
4
6
8
10
12
14
16
Pressure Loss (PSI)
1 1/2" and 2" w/LP Diaphragm and Spring
Pressure Loss Vs. Flow
350
Maximum Flow Rate is 265 GPM for a 2 inch valve (shown) and 176 GPM for 1 1/2 inch valve
300
Flow
(GPM)
Flow (GPM)
250
200
150
30 PSI Inlet, Maximum 265 GPM
20 PSI Inlet, Maximum 265 GPM
100
15 PSI Inlet, Maximum 244 GPM
10 PSI Inlet, Maximum 190 GPM
50
0
0
2
4
6
8
10
Pressure Loss (PSI)
12
14
16
Open-Close Operation
3" (3C) w/LP Diaphragm and Standard Spring
Pressure Loss Vs. Flow
600
Maximum Flow Rate for this valve is 419 GPM
Flow
(GPM)
Flow
(GPM)
500
400
300
30 PSI Inlet, Maximum 419 GPM
20 PSI Inlet, Maximum 419 GPM
200
15 PSI Inlet, Maximum 385 GPM
10 PSI Inlet, Maximum 176 GPM
100
0
0
2
4
6
8
10
12
14
16
Pressure Loss (PSI)
4" w/LP Diaphragm and Spring
Pressure Loss Vs. Flow
900
Maximum Flow Rate for this valve is 834 GPM
800
Flow(GPM)
(GPM)
Flow
700
600
500
400
30 PSI Inlet, Maximum 834 GPM
300
20 PSI Inlet, Maximum 593 GPM
200
15 PSI Inlet, Maximum 398 GPM
100
10 PSI Inlet, Maximum 214 GPM
0
0
2
4
6
8
10
Pressure Loss (PSI)
12
14
16
Open-Close Operation
6" and 8" w/LP Diaphragm and Spring
Pressure Loss Vs. Flow
2500
Maximum Flow Rate is 1,764 GPM for a 6” valve (shown) and 1,852 GPM for an 8”valve valve
Flow (GPM)
2000
1500
1000
30 PSI Inlet, Maximum 1981 GPM
20 PSI Inlet, Maximum 1910 GPM
500
15 PSI Inlet, Maximum 1710 GPM
10 PSI Inlet, Maximum 990 GPM
0
0
2
4
6
8
10
12
14
16
18
Delta P (PSI)
Operation with a Pressure Reducing Pilot
1" Valve with 3-way pilot (gray spring)
M a x im u m Flo w ( G P M )
Line Indicates Maximum Flow for Given Upstream and Dow nstream Pressure
80
70
Maximum Flow Rate for this valve is 53 GPM
60
50
40
30
20
6 PSI Downstream
8 PSI Downstream
10 PSI Downstream
10
0
10
20
30
Upstream Pressure (PSI)
40
Operation with a Pressure Reducing Pilot
2" Valve with LP diaphragm and 3-way pilot (gray spring)
Line Indicates Maximum Flow for Given Upstream and Dow nstream Pressure
Maximum Flow Rate for this valve is 265 GPM
250
200
150
6 PSI Downstream
100
8 PSI Downstream
50
10 PSI Downstream
0
10
20
30
40
Upstream Pressure (PSI)
3" (3C) with LP Diaphragm and 3-way pilot (gray spring)
Line Indicates Maximum Flow for Given Upstream and Dow nstream Pressure
Maximum Flow (GPM)
M a x im u m F lo w ( G P M )
300
700
600
Maximum Flow Rate for this valve is 419 GPM
500
400
300
200
6 PSI Dow nstream
8 PSI Dow nstream
10 PSI Dow nstream
100
0
0
10
20
Upstream Pressure (PSI)
30
40
Operation with a Pressure Reducing Pilot
4" with LP Diaphragm and 3-way pilot (gray spring)
Line Indicates Maximum Flow for Given Upstream and Dow nstream Pressure
M a x im um Flow (GP M )
1000
Maximum Flow Rate for this valve is 838 GPM
800
600
400
6 PSI Dow nstream
8 PSI Dow nstream
10 PSI Dow nstream
200
0
0
10
20
30
40
Upstream Pressure (PSI)
6" with LP Diaphragm and 3-way pilot (gray spring)
Line Indicates Maximum Flow for Given Upstream and Dow nstream Pressure
M a x im u m Flo w ( G P M )
2000
Maximum Flow Rate for this valve is 1764 GPM
1600
1200
800
6 PSI Downstream
8 PSI Downstream
10 PSI Downstream
400
0
10
15
20
25
Upstream Pressure (PSI)
30
35