Gents,
I have not had the opportunity to have cavitation or problems with fuel
vaporization on my or any of my 914 engine installations.
I have had problems with the pumps pulling air from gascolators in the
Europa. I do not install them for a number of reasons, primarily as the
tank is lower than the gascolator (so the gascolator doesn't trap water,
instead it only can trap large particles (which the tank screen should
do), act as a filter), and should the seal be just a bit loose or
broken, air is sucked into the fuel lines by the pump and in some cases
the pump can not self prime. I have also had loose filters, and other
things as below.
The main problems I have seen are:
The fuel fittings or selector valves which are too restrictive (less
than 1/4 inch ID for the fuel). Avoid items of cheap quality (normally
brass from China).
The Purolator fuel filters are assembled too loose and suck air by the
gasket when the pump is engaged.
Note that under high flow rates over 10 GPH the Purolators do cavitate
the fuel. Not so under normal operations.
The fuel filter is assembled backwards by the owner.
Gascolators installed of dubious quality/or maintained poorly, with
wrench marks and dented cans from excessive force used to install or
remove them. Once the seal is broken, one may not see a leak but prime
is lost, especially at low fuel tank levels.
Owner uses a unique fuel line installation which goes next to the
muffler, then over the top of the engine to the carb on a 912S without
any fire sleeve.
Kinked fuel lines in the central tunnel unnoticed during the build.
Auto filters using cheap paper which restrict fuel flow if wet. Test
Test Test non aviation filters.
Failure to install fire sleeve, instead they use thermosleeve which
holds radiated heat away but has no insulation.
Vaporization also is more common when the lines are routed so as to have
a bend forming a high spot in line, in a hot area of the engine
compartment. This is a problem in the tail dragger Europa as the
highest spot in the fuel system is the top of the engine, so a vapor
bubble from heat can form easily when attempting a hot start.
The 914 has a noticeable return flow and the 912S has an orifice that
allows modest flow and allows the vapor to bleed if the orifice is near
the carbs and not really low in the return line at the tank. The new
912 fuel manifold seems to work well mounted up on the cross over tube
in the trigear.
Fuel pumps normally take care of any heat problems in the fuel as cool
fuel flows quickly through the system. However if the engine is off,
fuel may not flow enough to cool the lines in a 912S that are installed
directly in contact with the top of the engine. The vapor then can
build up in the high spot on top of the hot engine. With the carb bowls
full of fuel, the cool fuel does not flow very fast past the orifice if
it installed very low. Hence the need that the orifice on the return is
high up to clear the vapor.
Some suggestions are:
If one is concerned about flow, two filters in parallel, properly
installed, could solve filter clogging where poor fuel quality is
common.
Install 3/8 lines to slow the flow, but this means less room in tight
spots and more connector step downs and more parts to buy.
Make sure you are assembling the fuel system in accordance with
acceptable methods and standards and or follow the Europa install manual
to the letter. After all, it works, but it is the minimum necessary to
do the job.
Failure to allow for sufficient cooling air in the cowl over the carbs
and fuel lines is a problem also, especially with the 912/912S. The 914
lines are at the rear and if clear of the exhaust and the fuel pump
delivers proper flow, all is well.
Stay away from ethanol laced gasoline as it vaporizes very well and
kills seals.
Be sure the fuel pump is of the proper size and type recommended as the
system is designed for that pump.
Hot start problems in the 914 can be irritating as the intake manifold
is quite warm after shutdown, as are the fuel lines and carbs. The
vapor in the carbs flows into the intake plenum and manifold and leaves
a super rich charge in the plenum which will delay start. Many of us
crank the engine with the fuel pump off or selector off until it hits,
then turn the pump/selector on to keep it running. At higher altitudes
and density altitude conditions, it is much worse.
This is not a cavitation problem but pure vaporization of fuel in the
intake of course.
Glad to confuse the issue.
Regards,
Bud Yerly
Tech Support
----- Original Message -----
From: William Daniell<mailto:wdaniell.longport@gmail.com>
To: europa-list@matronics.com<mailto:europa-list@matronics.com>
Sent: Monday, October 29, 2012 10:08 AM
Subject: RE: Europa-List: Vapour lock? Why?
Mmm yes thanks. It would seem to me that the two fuel lines offer an
opportunity to insert redundancy in the fuel filters.
Will
From:
owner-europa-list-server@matronics.com<mailto:owner-europa-list-server@ma
tronics.com> [mailto:owner-europa-list-server@matronics.com] On Behalf
Of Bob Harrison
Sent: 29 October 2012 08:20
To: europa-list@matronics.com<mailto:europa-list@matronics.com>
Subject: RE: Europa-List: Vapour lock? Why?
I use two Mini Andair Gascolators one on each fuel line for my 914 and
one was satisfactory when I had the early gas guzzling Jabiru 3300 and
was the butt of all fuel dispensing pump sites.
Regards to all.
Bob Harrison G-PTAG
From:
owner-europa-list-server@matronics.com<mailto:owner-europa-list-server@ma
tronics.com>
[mailto:owner-europa-list-server@matronics.com]<mailto:[mailto:owner-euro
pa-list-server@matronics.com]> On Behalf Of GRAHAM SINGLETON
Sent: 29 October 2012 12:40
To: europa-list@matronics.com<mailto:europa-list@matronics.com>
Subject: Re: Europa-List: Vapour lock? Why?
Best one is an Andair, not cheap though. The old Mini gascolator is
too small for a 914, GAS375 would be the one
Graham
-------------------------------------------------------------------------
-----
From: William Daniell
<wdaniell.longport@gmail.com<mailto:wdaniell.longport@gmail.com>>
To: europa-list@matronics.com<mailto:europa-list@matronics.com>
Sent: Monday, 29 October 2012, 11:31
Subject: RE: Europa-List: Vapour lock? Why?
I plumbed those in =93 following the book =93 but I see
they are probably not the ideal.
So what=99s the most common solution?
Will
From:
owner-europa-list-server@matronics.com<mailto:owner-europa-list-server@ma
tronics.com>
[mailto:owner-europa-list-server@matronics.com<mailto:owner-europa-list-s
erver@matronics.com>] On Behalf Of GRAHAM SINGLETON
Sent: 29 October 2012 05:29
To: europa-list@matronics.com<mailto:europa-list@matronics.com>
Subject: Re: Europa-List: Vapour lock? Why?
Nigel
another problem with those filters is that sometimes they look clean
but aren't because the contamination is translucent when wet with fuel;
so, more restriction.
You're right, they are too small. quite high fuel flow with a 914.
Graham
-------------------------------------------------------------------------
-----
From:
"nigel_graham@m-tecque.co.uk<mailto:nigel_graham@m-tecque.co.uk>"
<nigel_graham@m-tecque.co.uk<mailto:nigel_graham@m-tecque.co.uk>>
To: europa-list@matronics.com<mailto:europa-list@matronics.com>
Sent: Monday, 29 October 2012, 10:01
Subject: Re: Europa-List: Vapour lock? Why?
On 31/07/2012 22:27,
klinefelter.kevin@gmail.com<mailto:klinefelter.kevin@gmail.com> wrote:
klinefelter.kevin@gmail.com<mailto:klinefelter.kevin@gmail.com>
Snip ....
.....I was chatting with Rob Seaton ( of Rotech in canada). He said he
learned how too small a fuel line and/or tortured routing can cause
"cavitation" at the pumps. So maybe your fuel filter(s), on the suction
side of the pump,are causing cavitation in the pump(s). Maybe due to the
size (restriction of flow) of the filter, even if they are clean.
........ Snip
Kevin, I think Rob Seaton may be on the money with this one.
A year or so back, I experienced a dead cut while flying a friend's
914 powered Europa on a hot day. Nifty application of fuel pump restored
the noise, but once safely back on the ground, I checked the filters
(all clean). This aircraft was fitted with Europa specified Purolator
glass shrouded filters that allow you to see the fuel flowing. At low
RPM, the filter appeared full, but as power was increased, the filter
began to fill with what I thought was air. My first action was to check
the pipework and security of connections - but everything seemed fine -
it was definitely not drawing in air from anywhere. I then concluded
that I had experienced vapour lock and left it at that.
Curiosity got the better of me and I started researching cavitation
and stumbled upon this very stilted, but interesting presentation on
Youtube. Take a look at the first minute from 00.20 - in particular, the
glass venturi. This was exactly what I saw in the Purolator filters.
http://www.youtube.com/watch?v=K_w3gcvA87I<http://www.youtube.com/watch
?v=K_w3gcvA87I>
My conclusion is that the Purolator filter has the correct mesh size
to trap contaminants, but the filter capacity is too small and creates a
pressure drop in the fuel line.
Nigel
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