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6
Domestic hot water cylinder connection
6.1 General
The cold water pipes are connected according to DIN 1988 and
DIN 4573 Part 1 (Fig.6.1 on pag. 9). All connecting pipes should
be joined using pipe unions.
A circulation pipe should only be connected if the domestic water
supply system is extensive because it causes high stand-by
losses. If circulation is required,
it must be equipped with an automatic function for interrupting
circulation operation.
All connecting pipes including fittings (with the exception of the
cold water connection) must be protected against heat losses ac-
cording to the German Federal Energy Efficiency Ordinance
(EnEV). Poorly
6.2 Drainage
A means of draining the cylinder should be provided in the cold
water connecting pipe during construction.
6.3 Pressure reducing valve
It is essential to equip the connecting pipe with a pressure reduc-
ing valve if the max. supply pressure could exceed the permissi-
ble operating overpressure of 10 bar. However, according to DIN
4709, the pipe pressure should be lowered inside buildings to a
6.4 Safety valve
A tested and non-closing safety valve should be installed where
the cylinder is connected to the system. No constrictions, e.g. dirt
traps, should be installed between the cylinder and the safety
valve.
Water should be able to flow (drip) out of the safety valve when
the cylinder is being heated up to compensate for the expansion
of the water and to prevent a severe build-up in pressure.
The safety valve overflow pipe must flow freely into a sewage
system without any constrictions. The safety valve should be
mounted in an easily accessible and observable location so that
it can be vented during operation of the system. A sign should be
fixed on the valve itself or in its vicinity with the following inscrip-
tion: "Water may be discharged from the air outlet pipe during
heating! Do not close!."
6.5 Check valve, test valve
A check valve (non-return valve) must be installed to prevent the
heated water from flowing back into the cold water pipe. Its func-
tion can be tested by closing the first isolating valve in the flow di-
6.6 Isolating valves
As illustrated in Fig.6.1 on pag. 9, isolating valves are to be in-
stalled on the cylinder in both the cold and hot water connection
as well as in the heating water flow and return.
EN-8
376760 / 372840 / 370080 / 376730 · FD 9801
insulated or uninsulated connecting pipes will lead to a loss of
energy which is many times greater than the energy loss of the
cylinder.
A check valve should always be fitted to the heating water con-
nection to prevent the cylinder from heating up or cooling down
uncontrollably.
The air outlet pipe of the safety valve connected to the cold water
pipe must always remain unblocked. The operational readiness
of the safety valve should be checked at regular intervals by
venting it.
level which still permits technical operability to reduce the gener-
ation of noise. Depending on the type of building, it may then be
worthwhile to install a pressure reducing valve in the cylinder in-
let.
Use only spring-loaded diaphragm safety valves that have been
tested.
The air outlet pipe should have at least the same cross section as
the safety valve outlet. If it is necessary for the air outlet circuit to
have more than two bends or if it is more than 2 m in length, an
air outlet pipe in the next largest nominal size should be selected.
It is not permissible for the air outlet circuit to have more than
three bends or to be more than 4 m in length. The cross section
of the outlet pipe located downstream from the collecting hopper
must be at least twice the size of the cross section of the valve in-
let. The safety valve must be adjusted so that the permissible op-
erating overpressure of 10 bar is not exceeded.
rection and opening the test valve. Only the water contained in
the short piece of pipe should be discharged.
WWSP 335 - WWSP 770
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