Power Regulation; Models With Manual Power Selection; Automatic Models - Miele S 247i Technical Manual

S 2xx, S 3xx & S 4xx Canister Vacuums
dustbag compartment, so producing a negative pressure at the floor
attachment. Air is then sucked into the appliance via the floor attachment and
takes dirt and dust particles with it.
Figure 4-3 is a simplified graph showing the relation between the two factors,
negative pressure "h" in mbar and air throughput "Q" in liters per second. The
suction power "P2" is the product of "h" and "Q" divided by 10.
It can be clearly seen that the maximum negative pressure "h" is developed
when the air inlet is completely closed, i.e. air throughput "Q" is zero.
Conversely, maximum air throughput "Q" is achieved when the air inlet is fully
open. In this case, however, no negative pressure "h" can be developed. The
optimum operating range is, therefore, at the upper area of the suction power
"P2" curve.
The floor attachment and other accessories greatly influence the effective
suction power:
1. A crevice nozzle, with its small opening, allows a large negative
pressure to develop with only a low rate of air throughput.
2. The floor attachment has a large opening and so allows only a low
negative pressure to develop but has a high rate of air throughput.
Note:
The above shows that the figure given on the data plate (e.g., P = 1500W) is
only a description of motor power and not a true guide to the vacuum cleaner
suction power.
4.4

Power Regulation

4.4.1

Models with Manual Power Selection

Power control with models S 310i - S 338i and S 410i - S 438i is achieved by
phase chopping, with a potentiometer operated by the power selector (if
applicable) providing the phase angle control.
4.4.2

Automatic Models

S 3xx series:
If the set power level is too high, the effort required to slide the floor
attachment across a closely woven carpet increases greatly as the suction
effect holds the attachment firmly on the floor.
With such carpets, a good seal exists between the floor attachment and the
floor so that a lower suction power provides effective dust extraction.
Dust extraction is as thorough as when operating at full power on a smooth
floor covering.
With automatic models, the power is set automatically via a negative pressure
switch to a level appropriate for the floor covering being cleaned.
This ensures that vacuuming is always performed at the optimal suction power
setting. Closely woven carpets will be cleaned with a lower power level thus
saving energy.
25
Technical Information