MAINTENANCE MANUAL
Speedster
page 28
Expansion valve on heat-exchanger system
The coffee water heating system consists of a heat-exchanger inside the steam boiler
and the coffee boiler with group. This entire system is filled with water only, no steam,
no air. At the entrance of the coffee water system a one-way valve, or check valve, is
installed to prevent hot water being pushed back into the fresh water lines.
When water is heated it will expand. As there is no room for the expanded water (no air
pockets, no way out) pressure will build up. The right hand pressure gauge indicates the
pressure in the coffee water heating system.
To keep this pressure within safety limits, an expansion valve is part of the system. The
expansion valve will release drops of water when pressure exceeds the set value. The
released water is directed into the discharge.
As soon as the brewing lever is moved to its middle (pre-infusion) position (group valve
open, no pump activated) the pressure will drop immediately to incoming line pressure.
When the lever is moved to the lower position the pump will be activated. The pump now
pressurises the entire coffee water system.
The expansion valve and one-way valve is a combined part in the Speedster (see figure
16). The vertical part is the one-way valve, the horizontal part is the expansion valve.
Figure 16. Showing combined expansion valve and one-way valve. Flow direction within
the one-way valve is upwards.
Easiest is to work with the machine heating up from cold. This will give a long trajectory
of heating up and thus expanding of water in the coffee water system such that a proper
adjustment can be made.
When the machine is at idle (boiler water already warm) the heating element is only
engaged for short bursts every once in a while and the water within the coffee water
system does not expand, at least not enough for a proper adjustment.
one-way part
expansion part
outer nut
