Reference
Modification no.
- 0 -
Page
34
Date
1997 02 01
Main
914 F
01476
9.2.3) Fuel pressure control
See Pic. 12 and 13.
The fuel pressure regulator Q is attached on the airbox.
Fuel pressure control is essential for flawless engine operation because it
keeps the fuel pressure permanently approx. 0,25 bar (3,6 p.s.i.) above the
varying airbox pressure.
Design and function of the fuel pressure regulator:
â—† NOTE: The arrows indicate direction of fuel flow.
The diaphragm W devides the regulator into the top fuel chamber E and the
air chamber R. The compression spring set by the adjustment screw T
establishes equilibrium of forces on the diaphragm at the fuel pressure 0,25
bar above the actual air box pressure on the other side.
â– ATTENTION:Each fuel pressure regulator is calibrated already when
supplied and does not need any further adjustment or main-
tenance.
â—† NOTE: The cast arrows on top side of pressure regulator are for
application of no significance as inlet Y and outlet U are
directly connected via the chamber.
Part of the fuel flow from the pumps (approx. 100 l/h) is routed back to the fuel
tank via the diaphragm controlled cone valve I thus establishing a pressure
0,25 bar higher in the top chamber (fuel side) than in the lower chamber (air
side).
Since the lower chamber is connected via the pressure line with the airbox the
pressure of the fuel entering the carburetor will be 0,25 bar above airbox/float
chamber pressure.
Fuel pressure = airbox pressure + 250 hPa
In 1000 m altitude with the prevailing atmospheric of approx. 900 hPa the
following values will arise at take off performance.
Fuel pressure = 1350 + 250 = 1600 hPa
Therefore the required delivery pressure of the fuel pump will be
1600 - 900 = 700 hPa
2
7
3
6
7
Pic. 12
Pic. 13
00104
4
5
8
fuel return
carburetor
airbox
1
00117
fuel return
fuel feed
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