O.S. Engines PA-104 Carb - 72504000 - Manual

INSTRUCTIONS FOR O.S. PA-104 PUMP SYSTEM
The O.S. PA-104 Pump System consists of the unique O.S. Type PD-04 diaphragm fuel pump and matching large-throat
carburettor (O.S. Type 46), and has been developed specifically for O.S. MAX-40SF, 46SF, 40VF and 46VF engines.
The O.S. Pump System provides more power and ensures that fuel is delivered to the carburettor at the pressure reguired to
maintain the optimum mixture strength, irrespective of fuel tank location or aircraft attitude.
Note: This pump system cannot be fitted to the O.S. MAX-40FSR or 45FSR since the Type 46 carburettor cannot be installed in these engines.
PRINCIPLE OF THE DIAPHRAGM PUMP
Diaphragm
(oscillates as the pressure in the crankcase varies.)
Negative and positive pressures occur in these
chambers in accordance with upward and down-
ward strokes of engine's piston.
Fig.1
Check Valve No.1. Negative pressure causes Check Valve 1to open and admit fuel from
tank to pump. Valve automatically closes under positive pressure to prevent reverse
flow.
Under negative pressure Under positive pressure
Check Valve No 2 Positive pressure opens Check Valve 2 and delivers fuel to carburettor.
Valve automatically closes under negative pressure to prevent reverse flow
Fig. 2
Figs 1 & 2 are merely diagrammatic to explain the principle of the
diaphragm pump. Actual construction is more complicated.
INSTALLATION OF PRESSURE NIPPLE AND CARBURETTOR
* Remove the crankcase cover-plate (backplate) from the engine.
Drill and tap cover-plate boss with M3.5x0.6 Metric thread and
fit nipple supplied.
Important! After tapping, be sure to wash out screw hole
thoroughly with kerosine.
Note:
For this modification, an M3.5 tap set, including a 2.9mm
drill for the pilot hole, is available as an optional extra
(Code No. 27901002). Alternatively, for owners who do
not care to do this work, a replacement cover-plate, complete
with nipple installed, is also obtainable (Code No.25407001).
* Refit cover-plate and install the O.S. Type 46 carburettor.
Make a pilot hole with
2.9mm drill.
Cut thread at least 5mm (3/16") deep
Nipple supplied
Fig. 3
PIPING
* For piping, use heavy duty silicone fuel tubing of approximately
2.5mm bore and 5mm outer diameter.
* A feature of the O.S. Pump System is that the fuel tank does
not have to be placed close behind the engine, but tube lengths
should be kept as short as possible. Take care not to cause any
kinks in the "plumbing".
IN (Tube A) P (Tube C)
Make sure that the length
of Tube C is less than
10cm (4 in.).
Fig. 4
TubeA
TubeB
Overflow
(Do not seal off)
Type 46 carburettor
PD-04
Fig. 5
Tube A: To draw fuel from the fuel tank to the pump.
Tube B : To deliver fuel from the pump to the carburettor.
Tube C: To deliver the crankcase pressure pulse to the pump.
INSTALLATION
Here are examples of typical installations. (Figs 6 & 7)
* The ideal location for the pump is one in which the center
of the pump is on the same level as the a x i s of the carburettor
barrel as shown in Fig. 6. In many cases, this cannot be achiev-
ed, precisely, within the existing structure of the airframe.
However, try to fit the pump as closely as possible to this
optimum location. If the pump is installed more than 5cm
(2 in) above or below the ideal position, there may be a slight
variation in fuel/air mixture strength between level and inverted
flight.
Type 46 carburettor
Carburettor center line
Fig. 6
PD-04 pump
Fix the pump on the firewall, front bulkhead, or side of the
engine compartment with 3mm self-tapping screws. It is advis-
able to insert a piece of sheet rubber between the pump and
mounting surface. DO NOT attach the pump directly to any
part of the engine.
If it is not possible to mount the pump as described, it may
be possible to wrap it in foam rubber and insert it into a con-
venient space in the engine compartment, but make sure that
it does not touch the engine itself.
Caution:
When installing the pump, take care that the vent hole in
the pump body is not obstructed.
Do not ill the tank from here,
or the pump may be damaged.
Disconnect here when
filling the tank.
It may be convenient to lead the pipes
outside the fuselage and connect with
approx. 40~50mm(l-1/2~2") length
of silicone tubing.
Fig. 8
Do not block or seal.
Fig. 7
Overflow
L-shaped nipple or aluminum
tubing.
Connect to the nipple
of the cover plate.
Silicone tubing
WARNINGS
* Do not dissassemble the pump
Never take the pump unit apart. Once the pump has been
dismantled, its original performance may not be restored when
it is reassembled.
* Do not insert anything into the nipples
Inserting a pin, etc., into the nipples and/or air vent hole is
likely to damage the pump and render it inoperative.
* Use fuel filters
Any foreign matter entering the Pump System may interfere
with its correct functioning and may even damage the pump
diaphragm. Be sure to filter, all fuel before filling the tank and,
most important, use a good quality fine filter in the delivery
tube between the tank and pump.
Fuel tank
Pump incorporates a regulator here
to maintain fuel outlet pressure at a
constant level.