Yes, I agree, this probably didn't need said... for most folks, if they know it. But, I don't find it odd, any more, to find anti-sypon loops installed on the suction side of an installation.

A while ago, from what I understand, and possibly even now, there were illustrations published in some of the more promenent literature that showed anti-syphon loops installed in the suction side. Then, and even now, folks fall for it, unless they are aware that anti-syphon valves work only when the fluid is pushed through, not sucked through.

For those that are not aware of it, many installations require them- toilets, as well as engines and gensets... any installation that exhausts water below the static or heeled waterline and does not have an air break in it.

Rudy
Briney Bug, Panama City, Fl

----- Original Message -----
From: "Rudy and Jill" rudysechez@yahoo.com

COMMENT
Many years ago I nearly had a sailboat sink under me  because of this.
The boat had recently been  refitted for a trans-Atlantic trip. The owner
was in too much of a hurry  to  carry out a thorough  sea trial so we
departed outbound.
One of the refits was  replacement of the engine. Unbeknownst to us  the
mechanics  had  also replaced the bilge pump discharge hose but not
installed an anti-siphon break.
We had a decent  sailing wind of 30 knots so we sailed with the lee rail
nearly buried . The owner  declined my suggestion  to shorten sail overnight
so we pressed  on.  and  took on water. The electric bilge pump  kept
pumping  but with the outlet  below the heeled waterline we  did not notice
until well past midnight when the failing battery  also knocked out the
navigation gear and the pump stopped.  Our first clue was  when the cabin
sole was under water and  the 3 foot bilge was already full.
.This was  in the days before GPS and VHF was just beginning to show up on
smaller  pleasure craft.  Lacking an accurate position other than my DR  we
simply kept hand bailing  till dawn.  Now I am much more careful in checking
out repairs  done by marina mechanics before embarking on any  voyage
FWIW  the Swedish Johnson pumps  are superior  with their build in  back
flow preventer. If we had  such a pump on board  this situation would never
have  happened.
Arild

Hi Lee

If you are asking for my thoughts, and even if you are not, here I go. On the surface, it appears that you've got the loop in the wrong system, but I may be overlooking something here. If I am, I sure hope someone corrects what I'm saying.

The critical issue is if there is an air break. Your black water tank, with its vent, would qualify as an air break, if the stuff enters at the top of the tank. If it enters at the bottom, then as soon as the inlet is covered, there is no air break.

I have essentially this set up on our holding tank... the flow goes into the top of the tank, drops from the top to the bottom and exists at the bottom. A vent is installed at the top. The air space, between the top of the tank and the top of the level of the fluid breaks any attempt to form a syphon.

With your macerator, I'm not sure. If air can get into the system in such a way to defeat any syphoning from occuring, then it wouldn't need to have an anti-syphon loop. If it cannot, then one should be installed, I would think.

Many folks depend on the impeller to stop any back siphoning, but I don't trust impellers in any system to keep water from back syphoning. It doesn't matter, to me, when the impeller keeps syphoning from occurring, but instead, when it doesn't.

Rudy
Briney Bug, Panama City, Fl

Rudy,

All of the stuff that dumps into  the 680 liter black water tank goes
to the bottom first. The macerator sucks from the bottom. The 2 inch
vent line comes off the top

There is a intake and discharge isolation ball valves on each side of
the macerator. they are normally locked closed.

To all, I purposely did NOT clip Rudy's comments because  it would
make this part of the conversation much harder to follow IMHO.

Lee
On 7 May 11, at 22:21 , Rudy and Jill wrote:

Hi Lee

If you are asking for my thoughts, and even if you are not, here I go.
On the surface, it appears that you've got the loop in the wrong
system, but I may be overlooking something here. If I am, I sure hope
someone corrects what I'm saying.

The critical issue is if there is an air break. Your black water tank,
with its vent, would qualify as an air break, if the stuff enters at
the top of the tank. If it enters at the bottom, then as soon as the
inlet is covered, there is no air break.

I have essentially this set up on our holding tank... the flow goes
into the top of the tank, drops from the top to the bottom and exists
at the bottom. A vent is installed at the top. The air space, between
the top of the tank and the top of the level of the fluid breaks any
attempt to form a syphon.

With your macerator, I'm not sure. If air can get into the system in
such a way to defeat any syphoning from occuring, then it wouldn't
need to have an anti-syphon loop. If it cannot, then one should be
installed, I would think.

Many folks depend on the impeller to stop any back siphoning, but I
don't trust impellers in any system to keep water from back syphoning.
It doesn't matter, to me, when the impeller keeps syphoning from
occurring, but instead, when it doesn't.

Rudy
Briney Bug, Panama City, Fl

[demime 1.01d removed an attachment of type application/pkcs7-signature which had a name of smime.p7s]

Lee, a 2" vent line... now that's a manly sized vent. I'm jealous! Rudy