Kärcher HDS 7/12 M, Service Manual

Page: 45 / 131

English 5.906-432.0 Rev. 00 (06/15)
45
The lack of water fuse prevents the burner from switching
on in case of missing or insufficient water volume and thus
protects the on-demand heater from overheating.
With an opened gun and a sufficient water flow the sole-
noid is lifted against the force of gravity in the cartridge.
The solenoid piston closes the contact of the reed switch.
This opens the fuel solenoid valve and the burner ignites.
The sieve in the water supply of the safety block prevents
the contamination of the lack of water fuse.
The lack of water fuse is a safety component and therefore
its locking screw is sealed.
The information regarding insufficient water volumes is
sent directly to the control PCB.
There, this message is evaluated as
–
lack of water fuse (shut-off of burner, see above) and as
–
Dry-run protection for the pump (switch-off device).
The lack of water fuse functions immediately.
It switches the burner off immediately in case of insufficient
water volume and back on after the water level has been
replenished.
The dry run protection is intitiated when the lack of water
fuse signals insufficient water volume for 2 minutes.
The appliance shuts off with a fault message and locks up.
Only by switching the device off and back on via the main
switch, it can be taken into operation again.
As the dry-run protection damages the pump in the long
run, there must always be a sufficient water supply.
The safety valve guides the entire flow rate of the pump to
the float container if the pressure switch or the overflow
valve is defective and thus protects the device and acces-
sories from inadmissibly high overpressure.
If the gun is open, the safety valve is closed and the entire
flow volume of the pump is transferred to the gun at oper-
ating pressure.
If the pressure in the high pressure system rises by ap-
prox. 20 bar above the permissible operating pressure, the
valve ball is lifted off the valve seat and part of the flow vol-
ume flows into the swimmer reservoir.
The opening pressure of the safety valve is adjusted with
the adjustment screw.
Rotation to the right increases the opening pressure, rota-
tion to the left decreases the opening pressure.
The safety valve is a safety component and therefore its
adjustment screw is sealed. Note
The safety valve is adjusted via the pressure increase in
the system with the burner turned on, so that it limits the
pressure increase to the max. permissible value (see
Specifciations) with the gun closed.
Then seal the settings.
6.19.3 Function water shortage safeguard and dry-run protection
6.19.4 Function of safety valve