Unit Function
HDS Middle Range / HDS Premium Range
Page 42 / 127
Service Manual 04.2008
2.17 Safety block
Safety valve
If the pressure switch or overflow valve are
defective, the safety valve feeds the whole flow
rate of the pump to the float tank and therefore
protects the unit and accessories against
impermissibly high overpressure.
When the handgun is open the safety valve is
closed and the whole delivery volume of the pump
is pumped to the handgun with operating
pressure.
If the pressure in the high-pressure system rises
by approx. 20 bar above the allowable operating
pressure, the valve ball (16) is lifted from the
valve seat (17) and part of the delivery volume
flows into the float tank. The opening pressure of
the safety valve is set using the adjusting screw
(12). Turn it to the right to increase the opening
pressure and to the left to reduce the opening
pressure.
The safety valve is a safety component and
therefore sealed at the adjusting screw (12).
Low-water protection and dry running
protection
The low-water protection prevents the burner
from switching on if there is no or insufficient
water and therefore protects the continuous-flow
heater against overheating.
When the handgun is open and the water flow is
sufficient, the magnetic piston (6) is pressed
against the spring (3). The magnetic piston (6)
causes the contact of the reed switch (5) to close.
This opens the fuel solenoid valve and the burner
ignites.
The strainer in the water inlet of the safety block
prevents dirt from getting into the low-water
protection.
The low-water protection is a safety component
and is therefore sealed at the screw plug (2).
Information about insufficient water is forwarded
directly to the printed circuit board. There this
message is evaluated as
– Low-water protection (burner shut-off, see
above) and as
– Dry running protection for the pump (unit shut-
off).
The low-water protection takes effect
immediately. It immediately switches off the
burner if there is insufficient water and switches
it back on again when there is sufficient water.
The dry-running protection operates if the low-
water protection signals an insufficient volume
of water for 2 minutes. The unit switches off with
a fault message and locks. The unit cannot be
started up again until it has been switched off
and on at the master switch.
As dry running damages the pump in the long-
term, ensure an adequate water supply is
provided at all times.
Note:
The safety value is adjusted with the help of
the pressure rise in the system with the
burner switched on, so that it limits the pres-
sure rise to the maximum allowable value
for the closed handgun (see Technical
Specifications). Then seal the setting.