Chapter 3 Functional descriptions
SMSO-2-02.03- 15.07.03 39
3.2.7 Rotary-vane type pump
The pump generates the pressure for all the systems in the
machine. It increases the pressure of the mains water supply
(local mains or fresh water container) to the brewing pressure
required for making coffee (7.5 bar). The pump is thus in op-
eration for every product serving, except steam.
The rotary-vane type pump has a dual effect by-pass system.
the feed bypass and the return bypass. The feed bypass for
this system makes it possible to have input pressure available
on the output side when the pump is at a standstill. The return
bypass has the opposite effect and enables water that is not
required to flow back from the pressurised side (outlet side)
back to the inlet side (input side). This makes it possible to
keep a constant set pressure.
In principle, the pump consists of two main components: the
drive motor and the pump housing with bypass system. These
main components are flanged together and connected by
means of a coupling.
Function
If the pump is not being driven by the motor, water flows
through the bypass system at the pressure of the supply water
mains into the pump outlet side. When the pump is in opera-
tion, the water flows from the inlet into the sliding hatch cham-
ber. The rotor and the sliding hatches convey the water to the
output side. Depending on the water consumption in the ma-
chine the water now flows into the machine with low water
consumption some of it passes back through the by-pass to
the inlet side of the pump.
Pressure setting
The spring-resistance pressing onto the return bypass over
the pistons is adjusted by means of a setting screw. Thereby,
either more or less pressure is built up on the pressure side of
the pump until the bypass valve opens and the excess water
flows back to the inlet side of the pump. The pressure can be
set only if all the outlet valves are closed. During the adjust-
ment process the system must be relieved of pressure at short
intervals by briefly opening a valve, i.e. any excess pressure
that has built up inside the system must be discharged. It is
only thus that the correct pressure will display on the
manometer (see programming instructions, system test
“setting pump pressure.) It must be possible to set the
pressure without making sudden changes.
The effective brewing pressure for preparing coffee depends
on the grinding degree, on the amount of ground coffee (cof-
fee powder), on the compaction pressure and the condition of
the brewing unit. If a pump is repaired or a new pump in-
stalled, the pump pressure must always be reset. If in the
closed system a pressure of 7.5 bar is set, this generally pro-
duces an effective brewing pressure (flow pressure) of around
7.0 bar during coffee preparation.
Pump with bypass valve
1 Pump housing
2 Sliding hatch chamber
3 Rotor
4 Sliding hatch
5 Valve seat
6 Bypass housing
7 Piston
8 Adjusting spring
9 Adjusting screw
10 Counter nut
11 By-pass system (feed and return)
12 Coarse filter to by-pass system
Feed bypass: When the pump is at a standstill water flows
to the output side of the pump under the pressure of the
water supply.
Drawing symbol
Illustration
To Next Page
Loading...
Need help?
General
