Operating principle
When the spring (1) compression is adjusted using the control knob (2), the force
2
balance acting on the valve plug (3) changes, thus 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
5
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 fitted.
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3
➪
➪
4
System operation
The job 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 behavior
is guaranteed at any closing condition of the system two-way zone
valves. In fact, once the position of the valve control knob has been
established, the threshold pressure value is more or less constant
as the discharge flow rate varies (see hydraulic characteristic
diagrams).
A proper valve sizing must guarantee 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.
Two-way
∆p
B
1 1
2 2
3 3
4 4
5 5
∆p
NOMINAL
Circuit resistance curve
with two-way valves
partially open
∆p constant
on the circuit
Pump curve
A
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Circuit resistance curve with
two-way valves fully open
∆G
50%
100%
Flow rate G
Setting
To regulate the valve, turn the knob to the required value on the
graduated scale: the values correspond to the differential pressure in
psi or meters w.g. to open the by-pass.
For a quick setup adjustment of the differential pressure by-pass
valve, use the following manual method. As an example, a hydronic
system with several zone valves: the system must be operating, the
zone valves must be fully open and the by-pass valve must be set to
the maximum value (a) (clockwise). Gradually open the differential
pressure by-pass valve using the control knob (counterclockwise).
Use a thermometer, or simply your hand, to check that the hot water
a) b)
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2
3 3
4 4
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c) d)
is flowing into the by-pass circuit (b). As soon as a rise in the
temperature is noted, turn control knob (clockwise) one half turn
closed so hot water stops flowing into the by-pass (c). Lock the knob
in this position (d) with the locking screw.
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(37 pages)
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