Product Overview
E
A
C
B
mH
2
O
1
2
3
4
5
6
D
519709A
E
A
C
B
mH
2
O
1
2
3
4
5
6
D
E
A
C
B
mH
2
O
1
2
3
4
5
6
D
519709A
E
A
C
B
mH
2
O
1
2
3
4
5
6
D
519502A
519600A
519700A
E
A
C
B
mH
2
O
1
2
3
4
5
6
D
519609A
E
A
C
B
mH
2
O
1
2
3
4
5
6
D
E
A
C
B
mH
2
O
1
2
3
4
5
6
D
519599A
E
A
C
B
mH
2
O
1
2
3
4
5
6
D
519566A
E
A
C
B
mH
2
O
1
2
3
4
5
6
D
519709A
E
A
C
B
mH
2
O
1
2
3
4
5
6
D
E
A
C
B
mH
2
O
1
2
3
4
5
6
D
519709A
E
A
C
B
mH
2
O
1
2
3
4
5
6
D
519502A
519600A
519700A
E
A
C
B
mH
2
O
1
2
3
4
5
6
D
519609A
E
A
C
B
mH
2
O
1
2
3
4
5
6
D
E
A
C
B
mH
2
O
1
2
3
4
5
6
D
519599A
E
A
C
B
mH
2
O
1
2
3
4
5
6
D
519566A
1
2
3
4
5
Two-way
TOTAL LOAD
PARTIAL LOAD
mH
2
O
1
2
3
4
5
6
mH
2
O
1
2
3
4
5
6
Dimensions
System operation
The purpose of the differential pressure by-pass valve is to maintain the
pump operating point as close as possible to its nominal value (point A
on the graph shown below). If the by-pass valve is not used, when the
flow rate in the circuit decreases due to partial closure of the two-way
zone valves, the head loss in the circuit increases, point B.
The by-pass valve, set to the nominal head value of the pump, limits the
increase in pressure, by-passing the flow rate ∆G. This occurs at any
closing condition of the system two-way zone valves. In fact, once the
position of the valve control knob has been determined, the threshold
pressure value is more or less constant as the discharge flow rate varies
(see hydraulic characteristic diagrams).
The valve must provide a sufficient flow rate by-pass to keep the pump
at its nominal operating point in all system operating conditions, for
example when the first zone valves are closed.
Code A B C D E Wt. (lb.)
519502A
3
⁄4" MNPT
3
⁄4" MNPT 2
1
⁄4" 2
5
⁄8" 5
11
⁄16" 1
519566A
3
⁄4" press
3
⁄4" press 2
3
⁄8" 2
3
⁄4" 5
13
⁄16" 1
519599A
3
⁄4" SWT
3
⁄4" SWT 2
1
⁄8" 2
1
⁄2" 5
9
⁄16" 1
Code A B C D E Wt. (lb.)
519600A 1" FNPT 1" MNPT 3
13
⁄16" 2
1
⁄16" 6
5
⁄8" 1.4
519609A 1" FNPT 1" SWT 2
13
⁄16" 2
1
⁄16" 6
5
⁄8" 1.4
519700A 1
1
⁄4" FNPT 1
1
⁄4" MNPT 3
15
⁄16" 2
11
⁄16" 7
3
⁄8" 1.5
519709A 1
1
⁄4" FNPT 1
1
⁄4" MNPT 3" 2
11
⁄16" 7
3
⁄8" 1.5
Operating principal
When the spring (1) compression is adjusted using the control knob (2),
the force balance acting on the valve plug (3) changes, modifying the
threshold pressure value of the valve. The valve plug opens, activating
the by-pass circuit, only when it is subjected to a differential pressure
sufficient to generate a thrust greater than the thrust exerted by the
spring. This allows the flow discharge through the outlet (4), limiting the
difference in pressure between the two points in the system where the
valve is installed.
Flow rate G
∆p
∆p
NOMINAL
Circuit resistance curve
with two-way valves
partially open
∆p constant
on the circuit
∆G
A
B
50% 100%
Circuit resistance curve with
two-way valves fully open
Pump curve