| T.R | Title | User | Personal
Name | Date | Lines |
|---|
| 511.1 | Vented Loops | PUNDIT::MCWILLIAMS | | Mon Mar 23 1987 16:52 | 39 |
| An anti-siphon loop or sometimes called a vacuum breaker,siphon
breaker, or vented loop is merely a "U" shaped peice of metal or
Marelon (glass re-inforced Nylon) with a valve at it's top. The valve
closes under pressure, but opens under vacuum. It is installed at the
highest point of a system so that water past the valve is not sucked
back into the bilge.
It will not prevent water from being forced from the outside down into
the bilge, if you are in a following sea, for that a flap valve over
the outlet is nice. One could also use a check valve, but they are
discouraged since they can clog, and if Murphy has anything to do with
it will clog in the shut position rendering the bilge output useless.
The typical system should look like this;
Vented Loop + \
/ \ Hose \
# =================== Bilge outlet
----------------------#----------------------\ Waterline
# |
\ Hose # |-------------- Rudder
\ # | \ |
\ # | \ |
\ # | \--
\ Bilge # |
\ Pump # |
-------------------+
As one can see the advantage of the vented loop is to allow all the
water past the valve to drain out, rather than a siphoning action to be
set up to suck back down in the bilge. This is important since the
length of the hose run from the vented loop is generally much longer
than the length up to the vented loop, and hence there can be a
lot of water contained in that hose.
/jim
|
| 511.2 | RE.2 Liquid Plumber | PHENIX::JSTONE | | Wed Mar 25 1987 17:54 | 4 |
| re.2
Welcome back! We had a nice time. I'm impressed by your knowledge
of plumbing!
|
| 511.3 | Venting the Anit-syphom Valve | AKO539::KALINOWSKI | | Mon May 17 1993 14:59 | 23 |
| If an anti-syphon valve is used as part of the holding tank system
(ie tank, pump, anti-syphon valve, wastegate ), I have read that
the top of the valve should be vented to keep the 'aroma' from coming
into the cabin.
My question is can I patch the valve tubing into the holding tank vent
line without problem, or could this cause problems should one of those
sanitary suckers be used on the other part of the holding tank outflow?
| <- holding tank vent line
|
+-----------+----------------+
| |
------ --------- ------- ====== -------
|head| |holding| |pump | || || |Waste|
| |=====|tank |==Y==========| |=====|| ||==========|Gate |
+----+ +-------+ || +-----+ +-----+
||
||
============= Deck Plate for vacumn
|
| 511.4 | | UNIFIX::BERENS | Alan Berens | Mon May 17 1993 16:10 | 33 |
| re .3:
An antisiphon vent is normally closed -- the only time it should open is when
the pressure inside the hose/piping is below atmospheric pressure. (Our
vent is under the sink cabinet in the head, and we've never noticed an
aroma problem from it.) Both the original vent and the better quality
replacement were not designed to be (and could not be) connected by a
hose or tubing as you've drawn.
The vent opening is quite small and our original one was quite prone to
clogging shut, which is why I replaced it with a better (and larger)
plastic one I got at a Westerbeke dealer.
As an aside, the system you've drawn is the one that was on our first
boat -- what an abomination. The usual plastic holding tank is somewhat
permeable to odor, and in this system the tank has a nasty habit of
always being full. Worse, if you pump the tank with the tank full,
you can create enough pressure in the system to cause leaks (I found it
very hard to get really good seals on the tank fittings). Better a
Y-valve and a system like:
+----+ Y-valve +-------+ +----+
|head| |holding| |pump|
| |==\ /====|tank |=======| |====== deck plate or back to the
+----+ | +-------+ +----+ seacock with another Y-valve
|
|
seacock
Now as long as you are enough miles offshore, you can pump directly
overboard.
Alan
|
| 511.5 | Think function. | NWD002::SASLOW_ST | STEVE | Mon May 17 1993 18:07 | 7 |
| I think you are confused on the function of the vented loop. You only
need a vented loop in your head system if your head or tank is below
waterline. This prevents sea water syphoning back into the tank or
overflowing the head. It is usually place just in front of your
discharge seacock. It is not placed between your tank and the deck pump
out fitting.
|
| 511.6 | what a hassle this stuff is... | AKO539::KALINOWSKI | | Mon May 17 1993 19:11 | 41 |
| re .4
>An antisiphon vent is normally closed -- the only time it should
>open is when the pressure inside the hose/piping is below atmospheric
>pressure.
I thought the vent was open until you started pumping, in which case
it will close.
>The usual plastic holding tank is somewhat
>permeable to odor, and in this system the tank has a nasty habit of
>always being full.
Was this a hard plastic tank or the bag type. I'd hate to think I've
dropped $400 for nothing (best of everything I could find short of
custom built tanks).
>Worse, if you pump the tank with the tank full,
>you can create enough pressure in the system to cause leaks (I found it
>very hard to get really good seals on the tank fittings). Better a
>Y-valve and a system like:
I am using the new white sanitation hose with double clamps and
teflon taped attachments. Would silicone sealent help?
> +----+ Y-valve +-------+ +----+
> |head| |holding| |pump|
> | |==\ /====|tank |=======| |====== deck plate or back to the
> +----+ | +-------+ +----+ seacock with another
> | Y-valve
> |
> seacock
on this setup , would the anti-syphom valve go before the seacock in
either path to keep the holding tank from backing up,or would i put
the valve between the pump and the connom connection to the seacock.
re.5
i meant seacock where I said waste gate. the Y valve is before the
pump in the diagram.
john
|
| 511.7 | | UNIFIX::BERENS | Alan Berens | Tue May 18 1993 10:06 | 41 |
| re .6:
Hmmm, actually, either normally open and closed by high pressure or
normally closed and opened by low pressure would work. If normally open,
then, yes, there would be the potential for noxious gas to vent into the
boat. There would also be a tendency for a normally open valve to allow
a little water to escape until the pressure closes the valve. This might
also promote corrosion or leakage due to salt crystals forming in the
valve opening. Now that you ask the question, I'm not sure which design
our current vent is. But since I've never noticed any smells
attributable to it, perhaps it is the normally closed kind. Wrote first,
thought later this time.
The tank on our first boat was rigid polyethylene. Even with teflon
tape, it is difficult to get the threaded plastic connections
permanently tight. Polyethylene is rather soft and deforms under load.
Apparently, too, some odor simply goes through the walls of the tank
even though one does not usually think of gas going through a solid.
(Years ago, as an undergraduate, I did a little work on an early
satellite experiment. The design team was concerned about the helium in
a cosmic ray detector escaping through the thin magnesium walls of the
detector housing. I helped with some testing to determine the escape
rate.) In reviewing holding tanks, Practical Sailor made the comment
that there are two kinds of holding tanks -- those that leak and those
that are going to leak. Certainly a cheery thought. Almost nothing
sticks to polyethylene, including silicone, so I don't think it will
help.
> +----+ Y-valve +-------+ +----+
> |head| |holding| |pump|
> | |==\ /====|tank |=======| |====== deck plate or back to the
> +----+ | +-------+ +----+ seacock with another
> | Y-valve
> |
> seacock
The anti-siphon loop would in the line from the seacock to the
Y-valve(s).
Alan
|
| 511.8 | HELP, advise needed! | SCHOOL::HOWARTH | | Tue May 18 1993 11:43 | 17 |
| Re: -1
Alan,
You mentioned odors getting through poly tanks in your earlier
notes. I am in the process of installing a 20 gal Todd tank and
now I'm worried. Can these things develop and odor problem?
The tank doesn't seem to be robust.
Does anyone else out there have a Todd tank installed? If so,
are you happy with it? The tank was in the $50-60 range but if
it is going to smell, I'll install something else before its
too late.
Thanks,
Joe
|
| 511.9 | you're a better man than I | MR4DEC::RFRANCEY | dtn 297-5264 mro4-3/g15 | Tue May 18 1993 11:57 | 11 |
| John,
The more I read about this installation, the more glad I am that you're
the one doing this work!
My next boat is going to already have this in place!
Regards,
Ron
|
| 511.10 | how 'bout a litter box? | UNIFIX::BERENS | Alan Berens | Tue May 18 1993 17:38 | 22 |
| re .8:
My experience with polyethylene tanks is limited to my first boat some
years ago and to discussions and articles. West Marine seems to think
the Todd tanks are good. (By the way, the West Marine 1993 master
catalog has a good description/discussion of holding tanks and
plumbing.)
Where do you find space for a 20 gallon tank? The space on our boat is
incredibly limited (by, among other good things, two 45 gallon drinking
water tanks) and I was lucky to get a five gallon holding tank into the
bilge. It was there or under the settee on which I sleep -- which I
decided was a really lousy place for it.
There is an alternative to a holding tank, one which our cat uses .....
a litter box (but we're thinking of training said furry cat to use the
toilet like a real human -- training it to flush is the really tricky
part). A friend of some friends actually does use a large bucket filled
with peat moss instead of a toilet and holding tank. Our friends are not
too thrilled by this when they use the boat.
Alan
|