TWL: Fw: Around the world, Day 12, Fuel management
Doug wrote:
So, from what Georges has told us, I can assume that there is a drain in the
bottom of those tanks? Also, it sounds like there are sight glasses all
over the place. This system sounds pretty nifty, but would it pass a CG
inspection? What happens if one of those valves or hoses fail, or if someone
whacks a sight glass with a wrench?
Since I am in the middle of reengineering the fuel system on Maana, this is a topic I've been researching lately. First off, instead of normal valves, you use sight glass valves. (thank you Alex) These valves contain an integral safety valve which does not impede the use of the valve for the sight glass, but if the sight glass breaks, the larger volume of fluid running through the valve causes the integral safety valve to stop the flow. Don't ask me how it works, maybe somebody else on the list knows.
The other thing is to use a protective covering over the sight tube, be it plastic or glass. Some advocate using a 2x4 or other length of wood with a groove routed down one face to protect the sight tube. The problem with this arrangement is that it is difficult to mount the protective board in such a manner that it is rigid and does not depend on the tube itself for placement. An alternative shown to me by a local commercial supplier of valves, etc., is to use a length of thick wall polycarbonate tubing, usually about 3" in diameter. (or maybe it was some other poly-something, I get the various poly-anythings confused) The tube is cut in half, mounted around the sight tube, then held together with a hose clamp top and bottom. The length of the tube is such that it is held in place by the valves above it and below it and no pressure can be placed on the sight tube. (For those that believe a "home engineered" solution is not as good as a factory solution, various commercial compan
ies make purpose built sight tube shields for which they'll be glad to charge you lot's of money. I'm assured by the supplier that this solution will work almost as well as the poly tube.)
And of course, as everybody else has pointed out already, the sight tube valves are closed unless you are actually taking a reading.
Jim McCorison
M/V Maana - 38' DeFever, Hull #2
Seattle, WA
Okay, so I've received lots of answers about the sight glass thing not
really being glass. I'm with everyone on that. And the "turn the valve off
when not in use" part, too.
I'm buying a custom tank for my go-fast boat, and was told by the tank guy
that in order to comply with USCG and ABYC regs, a fuel tank can have no
ways for the fuel to drain out- it must be pumped out of the top. Any
mechanical failure results in the fuel just sitting there.
So, if a brain-dead person couldn't get the sight glass valve open, and used
a 12" crescent wrench to assist, and snapped off the valve, there would be
flooding of fuel. And any kind of gravity-feed situation, like Georges wrote
about, implies that fuel can flow out of the tank, all by itself. Ergo, I'm
confused about sight glasses and Nordhavn fuel systems vis a vis the regs.
Doug Barnard
currently in design phase of
"Iron Lotus"
48' X 16' X 4'3" X 22T origami steel trawler
Hi Jim,
Excellent post! If I may I'd like to expand on a couple of items.
----- Original Message -----
From: "Jim McCorison" jim@mccorison.com
These valves contain an integral safety valve which does not impede the
use of the valve for the sight glass, but if the sight glass breaks, the
larger volume of fluid running through the valve causes the integral safety
valve to stop the flow. Don't ask me how it works, maybe somebody else on
the list knows. <
When using 'real' sight glass valves it's important to put the right valve
in the right place. The top and bottom valves are different. The bottom
valve incorporates a captive ball bearing in the flow path of the liquid.
Being heavier than the liquid the ball sinks to the bottom of its chamber
which allows the liquid to flow around it into the glass. When something
causes the flow rate to increase the ball is forced upward to seat against
the outlet and prevent flow. Breaking the sight glass is one reason that the
flow rate could increase but there is another reason as well. Consider this
scenario: You're using good safety practices and shutting the valves off
except when you are actually taking a reading; Now you visit the fuel dock
and fill up; Now the fuel level in the tank is quite a bit higher than it is
in the glass; At the end of the day you decide to check the fuel level so
you crank the valve wide open; The fuel level in the glass rises about an
inch and stops. Opening the valve too quickly can essentially simulate the
breakage of the sight glass. It's no big deal really, you just close the
valve and the open it again but s l o w l y. I only mention this
because I've seen professional tank installers get confused by this
property.
The other thing is to use a protective covering over the sight tube, be it
plastic or glass. Some advocate using a 2x4 or other length of wood with a
groove routed down one face to protect the sight tube. The problem with this
arrangement is that it is difficult to mount the protective board in such a
manner that it is rigid and does not depend on the tube itself for
placement. <
Two things about this:
First, sight gauge valves are made with provision to mount a pair of brass
rods on either side of the tube. I personally think that these rods don't
provide enough protection. OTOH: It is some protection at least and I've
seen boats that left the sight glass completely exposed.
Second, I'm a big advocate of the grooved 2X4 approach. Paint it flat white
and you'll have sufficient contrast to read the glass in anything brighter
than total darkness. Now, with the indulgence of a patient fuel dock
operator, you can put big, easily read calibration marks on the board so
you'll know, at a glance, what the sight glass reading means. Finally,
properly mounted, this method will yield sight glass protection that is
virtually bulletproof for very little money.
WRT mounting the 2X4: What we did on tanks that we loaned to customers was
to weld steel tabs to the tank at levels corresponding to the top and bottom
of the sight glass. The board was then screwed or through bolted to the
tabs. Obviously that's most easily done on a newly fabricated steel tank. If
welding isn't an option I suspect the tabs could be attached with some sort
of adhesive (3M 5200 comes to mind).
As to Doug's question about compliance with USCG & AYBC regs: Sight glasses
and other potential gravity tank drains may well be outside the regs. OTOH:
Sight glasses and sediment drains aren't uncommon and I'm sure that I've
seen them on boats other than Nordhavens. If you'll send me a concise
(pithy?) version of that question I'd be happy to forward it to Georgs and
Jim L.
Visually yours,
Alex
----- Original Message -----
From: "Doug Barnard" dbarnard@virtualacreage.com
.......was told by the tank guy
that in order to comply with USCG and ABYC regs, a fuel tank can have no
ways for the fuel to drain out- it must be pumped out of the top.
..........I'm
confused about sight glasses and Nordhavn fuel systems vis a vis the regs.
Is your go-fast gasoline powered?
Regards,
John Gaquin
m/v Brefnie Queen, 32' Luhrs
blocked and wrapped @
Bass River Marina, West Dennis, MA
dbarnard@virtualacreage.com writes:
And any kind of gravity-feed situation, like Georges wrote
about, implies that fuel can flow out of the tank, all by itself.
Ergo, I'm
confused about sight glasses and Nordhavn fuel systems vis a vis the
regs.
On an earlier boat, a custom built 34 footer with a SABB Diesel, I
had a round-bottom tank (a bit like a beer- keg) with a hemispherical
collector bulb on the bottom. Fuel would be drawn from the barrel
itself. The collector bulb on the bottom had a drain-valve (like on
an automotive radiator). I would open this valve twice a year (spring
and fall) and drain all the sludge and water into a bucket. I always
had clean fuel without fancy Racor etc filtration. I and previous
owners also never had a problem with Diesel leakage.
These rules about no bottom drain seem to me from some bureaucrats
dreams. First opportunityI get, I shall install a drainbowl on my
existing tank. Rules or no rules.
George of Scaramouche1, Lake Ontario