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uvtreith(at)t-online.de
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 Posted: Thu Jun 07, 2012 1:45 pm Post subject: 2. electric fuel pump |
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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
[quote][b]
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budyerly(at)msn.com
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| Posted: Thu Jun 07, 2012 8:14 pm Post subject: 2. electric fuel pump |
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<?xml:namespace prefix="v" /><?xml:namespace prefix="o" /><![endif]--> 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
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