I have to disagree with those that say the Benwick system is a bad one. Many
people (including myself) have used them without problems. I am aware that
the restrictor is a potential hazard if it were to become blocked by a lump
of dirt but there shouldnt be lumps that size floating around any fuel
system. Fitting a small (sintered brass) filter just before the sensor will
eliminate any risk of such a blockage occurring.
The size of the restrictor may look small but I seem to recall that it is
larger than the shank end of a 1/16 in drill. If you have lumps of muck this
size in your fuel then you are bound to have problems sooner or later
whether you have a flowmeter in the line or not.
For the record our original fuel flow tests (with the sender in situ )
exceeded the maximum flow required by over 100%. On the rotax 912, 25
litres per hour (maximum flow) equates to 416 millilitres per minute. From
memory our fuel system was delivering in excess of 1200 millilitres per
minute (72 litres per hour). This was with both pumps working (ie:
electrical and mechanical),
and shutting down the electrical pump made very little difference to the
readings. We have a fuel pressure sensor on the carb side of the flowmeter
and never experience low pressure readings (ie: below 4psi).
The main filter in our system is incorporated in the gascolator - not an
Andair, but a flat steel gauze incorporated in the top of the gascolator
housing. As an
additional precaution, ALL fuel that we use is filtered through a gauze mesh
filter funnel (the type with the water trap) . Relying on the aircrafts
filters to keep the dirt out is IMHO taking an unnecessary risk.
If you are experiencing a drop in pressure in your fuel system I would look
elsewhere for the cause of the problem, possibly a clogged main fuel filter.
If the installation is new it is a real possibility due to the crud in the
tank.
The Benwick fuel flow sensor itself can be purchased from RS components.
Go to www.rsww.com and the part number is 256-225 (described as a
Liquid Flow Sensor Dual Range). Unfortunately the price has rocketed since I
last looked to 78 plus VAT. Used to be about 30 !!!
If you are simply looking to replace an existing sender, then I dont see the
point of replacing the whole system. If you are shopping around for a new
system than maybe the flowscan is a better bet (as long as you can get it
shipped to the UK without additional costs and taxes (ie: VAT).
If you have purchased a Benwick, dont throw it away. Properly installed
there is nothing wrong with it.
Hope this helps,
Carl P
G-LABS
----- Original Message -----
From: "nigel charles" <nigelcharles@tiscali.co.uk>
Subject: Re: Europa-List: Benwick FM 1053 Fuel Flow Computer
<nigelcharles@tiscali.co.uk>
>
> Hi William
>
> >I was unaware of this knowledge about Benwick, but I must say I have
never
> seen a drop in fuel pressure (sample point down stream of Benwick) at full
> throttle (mine's the 912). <
>
> You probably won't. However if you do the fuel flow check you are bleeding
> off an extra 25% above your max fuel flow. The restriction will then cause
> the pressure to drop just below the minimum (about 2.25psi if my memory
> serves me correctly). Practically speaking your setup is OK provided you
get
> no contamination in the sender causing fuel starvation. This has happened
at
> least once
> with the Benwick sender and I believe the PFA got close to banning fuel
flow
> senders. I am still surprised they allow use of the Benwick
> sender.
>
> >> Where can I buy a Flowscan sensor and are they
> directly interchangeable, or do I have to throw the Benwick unit away?<
>
> I bought mine direct from Floscan in Seattle (about $160 but money well
> spent). I haven't got their contact details to hand. Try Google. If no joy
> remind me in a couple of days time and I will look it up for you. The
> Floscan is cast alloy and comes with 1/4" female NPT threads. Either
> incorporate it into a rigid pipe system or buy a couple of adaptors to
mate
> with the 5/16" rubber hose.
>
> Regards
>
> Nigel
>
>
|