Bruno,
I am not sure what engine you have and which Piersburg pump you are
using.
For the 914:
I was content with the parallel pumps for years. The Piersburg pumps
operate pretty well either together or separately as the vane type pumps
do not allow significant back flow. However, the series style now
considered standard with bypass check valves, is designed to prevent any
problems, allow the pumps to operate together (as on takeoff for hands
free change if one pump fails on takeoff), or singly for normal cruise
operations.
We were never worried about priming the pumps so the location of the
pumps low or higher was not necessary. We were most concerned about the
actions necessary in the event of a pump failure on takeoff or landing
with the 914 and rapid priming in the event of fuel starvation from fuel
mismanagement.
If you use the double switch idea, you only get one pump at a time (If
you have a 912 that may be OK.), which lowers pressure and flow a bit
and in the event of a failure of the engine due tolack of fuel, the
pilot in a critical situation must first fly the plane and then go
through a switch change to hopefully catch the engine before it stops or
perhaps is required to focus on his flying skills rather than correcting
the engine problem.
The Rotax standard fuel pump installation model now is considered the
best case scenario for critical phases of flight for the 914.
First: On takeoff or landings select:
Main tank, (or Reserve if main tank is very low)
Main boost pump on
Aux pump on (This pump is not only battery driven, if the battery
fails, the alternator supplies current to continue its operation.)
Aux pump off (When at a safe altitude on takeoff and returned to on when
beginning descent or when operating at low altitude.)
This covers many potential failures:
Main tank has its own filter and with a change to reserve, a new filter
and tank side clears up supply problems.
Main boost pump on allows full fuel flow and should the aux pump fail
internally, the check valve will allow continued fuel supply around the
failed pump (either a fully blocked pump or a fully open line as if the
vanes completely shear off).
The Aux Boost pump can operate unobstructed as above and has a second
source of power. It is powered by the alternator and battery. Even if
the main contactor or battery completely dies, the alternator will allow
the aux pump to operate.
All the above on takeoff or landing requires no action on the part of
the pilot in the event of a pump failure. With the pumps placed as low
as possible in the aircraft the head pressure of the fuel in the tank
should quickly prime the pumps.
Once at a safe altitude, should the engine begin to misbehave, as in
your system the pilot only needs to:
Turn on the Aux Boost Pump
Switch tanks to the Reserve.
These two actions supply the pumps with a clean filter and a new fuel
source, turn on a second pump to increase potential fuel flow and
provide a secondary power source should the problem be electrical.
Refer to chapter 5 of the Europa Rotax 914 Installation Manual for the
best drawing of the fuel plumbing.
Refer of course to Europa Build Manual Chapter 25 page 11 for the
drawing of the electrical or the Rotax 914 installation manual.
As I check out a number of folks in the Europa, as well as answer many
emergency procedure questions, the design set forth in the Rotax and
Europa instructions allow a easy to teach and use system and to quickly
clear up fuel system component failures. True there are more fittings
to potentially leak, but good quality hose and clamps make that a non
problem. I have converted to R9 hose and with proper clamps, properly
tightened (that is, not over-tightened to cut the hose), it gives years
of service.
One note of caution:
Refrain from using inexpensive paper element filters. These filters
when exposed to water tend to have their paper filter material swell and
significantly restricts the fuel flow.
Should water be in the fuel, even in small amounts, the paper element
may swell and restrict flow. The problem of this restricted flow is
that the Piersburg or even the less complex Facet pumps will have a
great deal of difficulty re-priming in the event of fuel mismanagement
and may not even supply the minimum engine fuel flow and pressure
requirements once primed. It is necessary to test the filters if you
are using other than a fuel filter element which allows water to be
trapped or flow through...
Best regards,
Bud Yerly
----- Original Message -----
From: UVTREITH<mailto:uvtreith@t-online.de>
To: europa-list@matronics.com<mailto:europa-list@matronics.com>
Sent: Thursday, June 07, 2012 5:44 PM
Subject: Europa-List: 2. electric fuel pump
Hallo Europa Family
For safety reason I want to install a second Pierburg fuel pump. Both
pumps are below the reservoir level.
In the Europa builder manual of the Rotax 914 and also in the manuals
---From Rotax they say two pumps in line (it is not series, as both pumps
have a bypass via check valves).
Others like Pierburg or other aircraft builder say pumps parallel,
connected to a double switch (Doppelschalter) where one positive cable
(say from the engine control) goes to one end and the other positive
cable for the auxiliary pump, which comes from a buss plate or direct
---From the battery goes to the second part of the switch. That means, when
the main pump fails you disconnect with the double switch this line and
immediately you have connected the good pump. A full bypass flow by
using the check valve lines as made with the inline installation is not
necessary, as this way would be good only by planes where the reservoir
would be above the engine like a Piper cub.
The parallel installation with the double switch (you must be sure
that at first one pump is shut off before the other pump will get
switched on) would be much easier with much less leaking points.
So keep it simple as possible.
Do you agree or is that rubbish?
Have always safe flights (never suspend the laws) and all the best,
Bruno
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