Mattress and Seat Systems Service Manual
Introduction
Page 7
6
Operating Principles
Refer to Figure 4 for a typical pneumatic system diagram and cell inflation cycle, and Table 2 for the
actual cell configurations.
All pumps have two pressurised air outlets. Air from the outlets is fed to separate cells or groups of cells
in the mattress or seat cushion via a rotary valve.
The mattress or seat cushion support cells are continuously inflated and deflated during a ten minute
cycle. During the cycle, air is pumped from one outlet to cells “A” (or “B”) for 4 minutes and 10 seconds.
This is followed by a period of 50 seconds when air is pumped from both outlets to cells “A” and “B”.
Subsequently, air is pumped from the other outlet to cells “B” (or “A”) for 4 minutes and 10 seconds, and
then a further 50 seconds with air from both outlets to cells “A” and “B”. During the period when air is
pumped from an outlet to one group of cells, the second set of cells is slowly vented to atmosphere,
causing them to reduce pressure.
In some of the mattress replacements or overlays, there is a third set of cells labelled “C”, which are
supplied from a static feed. This static feed “C” is generated by two partial non-return valves (in the
mattress manifold assembly) from alternating feeds “A” and “B”, and is therefore never at zero pressure.
Where fitted, the “C” cells are normally in the head section of the mattress, to provide a stable pillow
section and prevent the patient’s head from rising and falling.
Figure 4 - Typical Mattress Pneumatic Diagram and Cell Inflation Cycle
Partial Non-return Valves
CPR
(where applicable)
Air Inputs
(where applicable)
Alternating Cells
Static
Cells
Alternating
1
Static
2
Alternating
3
Static
4
Head End
Feet End
Manifold Assembly
(where
applicable)
