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Old 30-08-2010, 15:45   #46
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Originally Posted by Dockhead View Post
... The pump doesn't prime.
... Now the installation instructions warn sternly that there must be no vented loop in the intake side. And in the trouble shooting part of the manual, it says again -- pump doesn't prime; remove vented loop...

Should I now put in a short length of hose bypassing the vented loop? I don't like the idea of not having it, despite what the Jabsco instruction manual says.
Temporarily tape up the vent, preventing it from breathing.
When that allows the pump to prime, you’ll know that you have remove or disable the vent.
A parallel bypass, that doesn’t disable the vent, will not work.
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Old 31-08-2010, 03:21   #47
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Temporarily tape up the vent, preventing it from breathing.
When that allows the pump to prime, you’ll know that you have remove or disable the vent.
A parallel bypass, that doesn’t disable the vent, will not work.
Not a bypass, but a substitute short path, to plumb the toilet the way the Jabsco instructions say. I would leave the vented loop in place for use in case of refitting a manual pump.

I will try your suggestion if I can find the d*mn thing. I think it's behind the cabinetry somewhere. The otherwise extremely detailed Moody manual does not for some reason have a schematic for the vented loops.

What do you think about Jabsco's instructions? Perilous?
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Old 14-09-2010, 03:01   #48
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Well, I found the vented loop, or anyone one vented loop in the supply side. Lo and behold, it is between the pump and the toilet bowl.

Jabsco want me to replace this with a short piece of straight pipe supplied in the kit. Yeah, right. They also want me to shut off the sea cocks after every single use of the toilet.

This vented loop is in my engine compartment. I will try to prime it by hand by screwing off the vent and pouring water in. This is on the OUTPUT side of the pump, so not sure how it could be the problem. Perhaps there is another vented loop between the sea cock and the pump -- I can't tell without ripping cabinetry out, which I'm loath to do at this point.

I could get rid of both vented loops as Jabsco insists, and without too much trouble, but I am loath to do this since the previous absolutely identical electric pump worked perfectly during the previous year of ownership, and since I definitely will not shut off the sea cocks every single time I take a leak.

This is frustrating. Anyone have any insights?


A couple of particular questions:

I understand that a vented loop prevents (or is supposed to prevent) siphoning of sea water into the boat. But it also prevents simple leaking of sea water, doesn't it? Downstream of the vented loop, an open pipe (a cracked pipe; clip fell off; hole in the pipe; etc.) won't leak anything.

So why would there be TWO vented loops in the supply side of the toilet? Why in the world would there be one between the output side of the pump and the toilet bowl? What possible function does it have?

Unless it is the ONLY vented loop, in which case the pump itself, the strainer, and all the piping between the pump and the sea cock are unprotected such that any leak will flood the boat -- I would have thought that the vented loop would belong further upstream, i.e., closer to the sea cock.

This: Click image for larger version

Name:	13_C.gif
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(From Installing a Head by Don Casey)

implies that the toilet pump is directly piped to the sea cock with no loop. Casey wrote:

"A vented loop in the inlet line can interfere with the proper functioning of the head, and its omission poses less risk because of the positive-action valve on the inlet side of the head. But if you leave the loop out, you must keep the inlet valve in good working order. A screen filter to exclude grass and other debris is highly recommended. If you want a vented loop on the inlet side, install it in the hose between the pump and the bowl."
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Old 14-09-2010, 05:06   #49
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In the Sh*t

I sympathise with every skipper that has ever had a toilet problem; it’s always the skipper’s problem. Crew, relatives, best friends, everybody suddenly has something else to urgently do somewhere else.
A vent in a pipe is a one way valve that lets air into the pipe but prevents water, or anything else, exiting the pipe into the boat. They are used on the pressure side of a pump (discharge side) but never on the inlet side. They are used to break the siphon that can otherwise occur back into a toilet or basin etc. that may be below sea level sometimes or always. If installed on the suction side of a pump they stop the pump from sucking water because they let air in, therefore “un-priming” the pump. But, if the vent is at or below sea level, a vent on the inlet side of the pump may not stop a weak pump from working because the vent is continuously pressurised by the sea itself. However, a new pump, with just a bit more suck, and if the vent is not much below sea level, the new pump will suck air through the vent that the old pump couldn’t. Ironically everything you’re doing to make the flow better, such as a new filter, is probably making the pump suck more air through the vent. A weak or semi-blocked pump could work fine as it wouldn’t suck air past the weak spring in the vent. So, yes, Jabsco is right, never have a vent on the inlet side of a pump.
Your pump-out idea is a great one, and because it’s sucking, when it works the problem exits. Once I used the salt water deck hose shoved up the under water discharge of the holding tank to slowly erode away the blockage, it took an hour or two (with me going for regular swims to jam it in tighter) before it got through the sh*t. The next time I put a cork in the vent pipe of the holding tank and pumped the manual toilet like hell. BANG! The cork shot across the bay like a bullet. So I took the vent pipe off the skin fitting, doubled it over and squeezed it in a pair vice grips to block it and pumped again. The boat was suddenly surrounded by a huge brown stain; success! In retrospect I should have double hose clipped the vent pipe to the holding tank before trying this trick as if it had come off I’d of had a boat full.
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Old 14-09-2010, 05:12   #50
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The next time . . . .
Yikes, those words -- "the next time" -- are chilling. How often do you have clogged plumbing? This was our first in decades, I was hoping that "the next time" would be more decades from now, when I am too dead to have to deal with it.
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Old 14-09-2010, 06:44   #51
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Yikes, those words -- "the next time" -- are chilling. How often do you have clogged plumbing?
No****! pun intended. I've only had one so far, but I haven't even had my boat for 2 years. Then I wound up having a small hairline crack in one of the fittings, then I had **** squirt out the side of the fitting, because I didn't tighten the new one enough for fear that I'd crack it again.

Next time...I'm installing a Nature's Head!

Seriously, just walking to the register at Lowe's with that new bottle of acid to keep the hose clean, really got me thinking even more that I'm ready to make that switch.
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Old 14-09-2010, 07:16   #52
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Dockhead,
I would suggest that you pull the inlet hose off the new pump and see if water flows out of it. Is the toilet installed so the rim of the bowl is about at the waterline?? If the only vented loop is downstream of the pump, it shouldn't affect the priming.
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Old 14-09-2010, 07:55   #53
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We were blasting Mahler in the cockpit, although we don't usually mix saiing with music.
Off (realistic but still disgusting) topic: "Why not"?!

I personally don't know any greater pleasure than surfing along with my boat, the amazing shades of water around me, bright sunshine to top it off and some classical music blasting from the speakers!
Be it Mahler, or Brahms or - needless to say almost "written for such occasions": Beethoven!
Mmmmmm!
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Old 14-09-2010, 08:05   #54
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Dockhead,
I would suggest that you pull the inlet hose off the new pump and see if water flows out of it. Is the toilet installed so the rim of the bowl is about at the waterline?? If the only vented loop is downstream of the pump, it shouldn't affect the priming.
I did this. It does not flow. Hmmm.
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Old 14-09-2010, 08:12   #55
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Off (realistic but still disgusting) topic: "Why not"?!

I personally don't know any greater pleasure than surfing along with my boat, the amazing shades of water around me, bright sunshine to top it off and some classical music blasting from the speakers!
Be it Mahler, or Brahms or - needless to say almost "written for such occasions": Beethoven!
Mmmmmm!
Well, when I listen to music I like to concentrate on it. I don't like music used as wallpaper. When sailing I am usually concentrating on sailing.

When communing with nature I like to concentrate on nature.

But this particular time there wasn't much to do in the cockpit as the wind was steady and we only had one sail up (well reefed). It was a deeply moving experience, to feel all that stupendous power of the sea and listen to Mahler's Seventh, at the same time, which seemed to be just written for the occasion, as you say. I'll never forget it.

I shot a short vid of it on my phone:
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