Code
A
B
C
D
E
Weight
(lb)
1” FNPT
1” MNPT
3
13/16
”
2
1/16
”
6
5/8
”
1.4
31076
1” FNPT
1” SWT
2
13/16
”
2
1/16
”
6
5/8
”
1.4
1
1/4
”
FNPT
1
1/4
” MNPT
3
15/16
”
2
11/16
”
7
3/8
”
1.5
31077 1
1/4
”
FNPT
1
1/4
” SWT
3”
2
11/16
”
7
3/8
”
1.5
E
B
D
E
B
D
E
B
D
E
B
D
E
B
D
Differential Pressure By-Pass Valve
31075-31077 series
BS EN ISO 9001:2000
Cert. n
∞
FM 21654
UNI EN ISO 9001:2000
Cert. n
∞
0003
01007/09 NA
Function
The differential pressure by-pass valve is used in systems with a
fixed speed circulating pump supplying several zones controlled
by two way zone valves. This valve ensures that the head pressure
of the pump is proportional to the number of two way valves being
closed. It will bypass the differential pressure created by the pump
as the zone valves close, thus eliminating water hammer noise.
31077 31075
Product range
Part # 31075 Adjustable differential pressure by-pass valve with graduated scale, flow up to 9 gpm Size 3/4" Sweat x 3/4" Sweat outlet
Part # 31076 Adjustable differential pressure by-pass valve with graduated scale, flow up to 40 gpm Size 1” Female NPT x 1” sweat outlet
Part # 31077 Adjustable differential pressure by-pass valve with graduated scale, flow up to 45 gpm Size 1 1/4” Female NPT+1 1/4” sweat outlet
Technical specifications
Materials
Body: brass
Valve plug: brass
Valve plug gasket:
EPDM
O-R ing
seals:
EPDM
Union seals: asbestos free NBR
Control knob:
ABS
Spring: stainless steel
Performance
Medium: water, glycol solutions
Max percentage of glycol: 30%
Temperature range: 32–230°F (0–110°C)
Maximum working pressure: 150 psi (10 bar)
Flow rates: 3/4” flow up to 9 gpm
1” flow up to 40 gpm
1 1/4” flow up to 45 gpm
Setting range: 1 - 6 m w.g. (2 - 10 psi)
Dimensions
519
502A
519
599A
519
600A
519
700A
519
609A
519
709A
1
2
3
4
5
mH2O 6
1
2
3
4
5
mH2O 6
1
2
3
4
5
mH2O 6
1
2
3
4
5
mH2O 6
1
2
3
4
5
mH2O 6
A
C A
A
C
C
A
C
A
C
Code
A
B
C
D
E
Weight
(lb)
31075
3/4” MNPT
3/4” MNPT
2
1/4
”
1
7/8
”
5”
1
3/4” SWT
3/4” SWT
2
1/8
”
2
1/2
”
5
9/16
”
1
1
TOT
AL
LOAD
➪
➪
P
A
RTIAL LOAD
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. 1
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
mH2O 6 mH2O 6
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)
1
2
3 3
4 4
5 5
mH2O 6 mH2O 6
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.
1
2
3
4
5
mH2O
6
1
2
3
4
5
mH2O 6
➧
➧
➧
0
0
0
0
1
1
5
2
2
10
0.5
3
15
3
4
20
4
5
1
25
5
6
6
30
7
1.5
8
35
7
9
40
8
10
2
45
9
3
G
(
m
3
/h)
(gpm)
G
(
m
/h)
(gpm)
0
0
1
5
2
10
3
15
4
20
5
25
6
30
7
35
8
9
40
G
(
m
3
/h)
(gpm)
6
Hydraulic characteristics
Part # 31075 (3/4”)
Part #31076 (1”)
∆p (psi) Setting positions
∆p (psi) (m w.g.)
∆
p
(m w.g.)
Setting positions ∆p (m w.g.) (psi)
11
10
10
11 8
10 7 7
8
11
7 10
9 9 6
8
8
8
9
6
6 8
7
6
7 5 5
5
5 7
6 6 4 4
5
4
5
4
4 6
3
5
4 4 3 3
3
2
3 2 2
2 2
1 1
1 1
0 0 0 0
2
3 4
1
2 3
2
1 1
0 0
Part # 31077 (1 1/4”)
∆
p
(m w.g.)
Setting positions
∆p (m w.g.) (psi)
8 8
11
7 7 10
6
6
6 9
8
5
5
5 7
4
4
4 6
3
5
3
2
3 4
2
1
2 3
2
1 1 1
0 0 0
Installation
The differential pressure by-pass valve can be fitted in any position,
respecting the flow direction indicated by the arrow on the valve
body.
In systems with a traditional boiler it is normally fitted between the
system flow and return ends, which allows the control of the pressure
and the passage of a minimum flow through the heat generator.
In systems with a condensation boiler, it is preferable to fit the
by-pass directly between the upstream and downstream sections
of the pump, as this allows a higher ∆T in the circuit, with lower
return temperatures and therefore better operation of the system.
In the event of high by-pass flow rate levels, it is recommended to
fit the valve between the flow and return ends of each column,
rather than fitting a number of valves in parallel at the central boiler.
Application diagrams
Shut-off valve
Pump
RT Room thermostat
Check valve
Insulated manifold
Two way zone valve
Autoflow
Thermostatic valve
Automatic air vent
Small-medium size system
by-pass in central plant RT
RT
Medium-large size system
by-pass on top of risers
1 1
mH2O 6 mH2O 6
RT RT RT RT
RT RT RT RT
V
Chilled water system, central by-pass
RT RT
RT RT
CHILLER
SPECIFICATION SUMMARIES
Differential pressure by-pass valve. Threaded connections 3/4” MNPT x 3/4” MNPT outlet, 3/4" Sweat x 3/4" Sweat outlet
1” FNPT x 1” MNPT outlet, 1” FNPT x 1” sweat outlet, 1 1/4” FNPT x 1 1/4” MNPT outlet and 1 1/4” FNPT + 1 1/4” sweat
outlet. Brass body. Brass valve plug. EPDM valve plug gasket. EPDM O-Ring seals. Asbestos free NBR union seals. ABS
control knob. Stainless steel spring. Medium: water, glycol solutions. Maximum percentage of glycol 30%. Temperature
range 32–230°F (0–110°C). Maximum working pressure 150 psi (10 bar). Setting range is 1 - 6 m w.g. (2–10 psi) and 3/4”
flow up to 9 gpm (1” flow up to 40 gpm and 1 1/4” flow up to 45 gpm).
We reserve the right to change our products and their relevant technical data, contained in this publication, at any time and without prior notice.
CALEFFI
Infloor Sales and Service
P.O. Box 4945, 503 Gregg Drive, Buena Vista CO 81211
Tel: 719.395.3400
/
Fax: 719.395.3400
/
www.Infloor.com
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