User guide

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Other Boiler Controls
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Other Boiler Controls
The DU144 automatic bypass valve controls water flow in the heating circuit according to the water
pressure across it and is used to maintain a minimum flow rate through the boiler and to limit circulation
pressure when other water paths are closed.
A bypass circuit must be installed if the Boiler manufacturer requires one, or specifies that a minimum
flow rate has to be maintained whilst the Boiler is firing. The use of automatic bypass valves becomes
particularly important when heating systems include large numbers of thermostatic radiator valves
(TRVs) - whilst the TRVs are open the automatic bypass valve remains closed, however, as the TRVs
start to close, the auto-matic bypass valve starts to open maintaining the required water flow through
the boiler. Using an automatic bypass valve is also likely to reduce noise in systems caused by excess
water velocities. Because manual or fixed position valves do not regulate the flow and allow water to
bypass even when it is not necessary, building regulations require bypass circuits to use automatic
bypass valves and not fixed position valves.
DU144
The DU145 automatic bypass and differential pressure valve is used to maintain a constant differential
pressure in a heating system. It reduces flow noise in a system, particularly as thermostatic radiator
valves are closed. The boiler return temperature is raised and this reduces corrosion caused by flue
gas condensation. In addition, when radiator valves are closed it also maintains flow over the
temperature sensor on the boiler to ensure proper operation of external temperature compensation
controls. On gas-fired water heaters it guarantees a minimum flow circulation when thermostats or
radiator valves are closed.
For pump-driven warm water heating systems, e.g.:
• On heating systems with three-way or four-way mixing valves, or
• on gas-fired hot water circulation heating systems.
DU144 Automatic Bypass Valve
Materials • Valve housing, fittings, bonnet and handwheel made of brass
• Spindle made of stainless steel
• All sealings made of EPDM and NBR
• Protection cap made of red plastic
Medium type water or water-glycol mixture according to VDI 2035
Media temp. 2 ... 110
o
C
Max. operating pressure 10 bar
Differential pressure
setpoint range
0,1 ... 0,6 bar
Kvs value 2,3
Product description Type
with compression fittings for 22mm copper pipe DU144A1001
with 3/4" external threads DU144A1002
with 3/4" internal threads DU144A1003
DU145 Automatic bypass and differential pressure valve
Materials Brass housing and fittings, plastic sping bonnet assembly and
valve disc, stainless steel spring, EPDM seals
Body pattern angle
Medium type water or water-glycol mixture according to VDI 2035
Max. media temperature 110
o
C
Max. operating pressure 3 bar
Differential pressure
setpoint range
0,1 ... 0,6 bar
Additional description For system capacities up to approx. 70 kW (60.000 kcal/h)