Operating principle
When the spring (1) compression is adjusted using the control
knob (2), the force 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 di rential pressure su
t to generate a thrust greater than
the thrust exerted by the spring. This allows the
w discharge
through the outlet (4), limiting the di rence in pressure between
the two points in the system where the valve is
System operation
O = open
C = close
The job of the di erential 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 ow 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
w 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
w rate varies (see hydraulic
characteristic diagrams).
A proper valve sizing must guarantee a su cient
w rate by-pass to
keep the pump at its nominal operating point in all system operating
conditions, for example when the rst zone valves are closed.
1
2
3
4
5
Flow rate G
∆
p
∆
p
NOMINAL
Pump curve
∆
p constant
on the circuit
Circuit resistance curve
with two-way valves
partially open
Circuit resistance curve with
two-way valves fully open
A
B
∆
G
50%
100%
Two-way
TO
TA
L
LOAD
mH2O
1
2
3
4
5
6
PA
RTIA
L
LOAD
mH2O
1
2
3
4
5
6
O
O
O
O
O
O
C
O
O
C
C
O
CAUTION:
All work must be performed by
d personnel trained in the
proper application, installation, and maintenance of systems in accordance
with all applicable codes and ordinances.
CAUTION:
Over-tightening and breakage can occur with the use of T
®
pipe joint compounds. T
®
provides lubricity so that care must be
exercised not to over-tighten joints. Failure to follow these instructions
could result in property damage and /or personal injury.
WARNING:
System
s are under pressure or temperature can be
hazardous. Be sure the pressure has been reduced to zero and the
system temperature is below 100°F (38°C). Failure to follow these
instructions could result in property damage and/or personal injury.
WARNING:
This product can expose you to chemicals including lead, which is
known to the State of California to cause cancer and birth defects or other
reproductive harm. For more information go to www.P65Warnings.ca.gov.
