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Old 12-07-2014, 13:39   #1
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Vented Loop to Head Whistles

When I pump my Jabsco Head the vent in the vented loop makes a loud noise which I'm calling a whistle but it's louder. I've tried several fixes including changing the small rubber duck valve to changing the entire vented loop fixture. With a new fixture I couldn't get the head pump to suck up the raw water. With a new duck valve the noise just continued. Your help is appreciated in advance.
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Old 12-07-2014, 13:42   #2
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Re: Vented loop to head whistles

The vented loop should be between the pump and the bowl, not on the suction line. Installed on the suction line it is doing its job and letting in large amounts Of air as you also try to pull water past it.
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Old 12-07-2014, 14:16   #3
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Re: Vented loop to head whistles

Okay, I'm lost and have to ask...isn't the purpose of the loop to prevent siphoning and siphoning can only occur from the raw water line, right? The Jabsco instructions show the loop on the line from the through hull via seacock to the pump with the loop placed above the water line.
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Old 12-07-2014, 14:21   #4
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Re: Vented loop to head whistles

The loop prevents siphoning by allowing air into a line to break the siphon. If you do have a siphon on a head, the bowl will fill, flow over and sink the boat. By putting the siphon break on the pump discharge, between the pump and bowl, well above the heeled waterline, you are breaking the siphon and allowing the pump to pull water without pulling air.
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Old 12-07-2014, 14:40   #5
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Re: Vented loop to head whistles

The loop doesn't go between the pump and bowl, it goes between the pump and outlet seacock.
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Old 12-07-2014, 14:47   #6
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Re: Vented loop to head whistles

That's what I'm saying. I think my error was installing the little rubber duck valve upside down.
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Old 12-07-2014, 14:50   #7
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Re: Vented loop to head whistles

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Originally Posted by savoir View Post
The loop doesn't go between the pump and bowl, it goes between the pump and outlet seacock.

He said that with the new vent the head wouldn't suck up water. Ideally there should be a vent between the seawater side of the pump and the bowl and between the pump and the poo out skin fitting.
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Old 12-07-2014, 14:51   #8
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Re: Vented loop to head whistles

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Originally Posted by Michael Ramos View Post
That's what I'm saying. I think my error was installing the little rubber duck valve upside down.

You said the the new vent prevented you from sucking water.....and it should if it's installed on the head seawater suction side of the pump. This is not the correct location.
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Old 12-07-2014, 15:05   #9
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Re: Vented loop to head whistles

You only put a loop on the inlet side if the bowl is beneath the waterline. That's pretty rare. The pressure on the inlet side is higher because the pipe is narrower, so a loop in that position might well whistle.
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Old 12-07-2014, 15:13   #10
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Re: Vented loop to head whistles

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You only put a loop on the inlet side if the bowl is beneath the waterline. That's pretty rare. The pressure on the inlet side is higher because the pipe is narrower, so a loop in that position might well whistle.

The loop on the suction side of the pump will whistle while pumping because of the high vole of air that is entering the line , caused by the vacuum created in order to move water. It will be noiseless in the correct position as the pressure closes the valve.
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Old 19-07-2014, 19:27   #11
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Re: Vented loop to head whistles

I have an electric Jabsco toilet with a anti siphon installed between pump and sea water inlet. There is an electric solenoid shut off valve installed at the bleeder hole for anti siphon. the power to solenoid is paralleled with the electric head pump.

Every time I use the head, the solenoid would shut off the anti siphon to allow suction from the pump at the bowl to pull in the sea water. Before I install this solenoid, I would get a loud whistling too .
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Old 19-07-2014, 21:00   #12
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Re: Vented loop to head whistles

Sailmonkey is correct. You should never put a vented loop on a suction line.

It is designed to let air into the line when it is under suction. This makes it harder for the pump to pull water in. The OP replaced a partially blocked vent and lost the ability to draw water into the pump.

If you are worried that water might siphon into the bowl from the intake, then the siphon break goes between the pump and the bowl. If you have a toilet, like the Groco K and many electrics, that don't have a hose between the pump and bowl, you need to use an electric siphon break like Ericoh88 describes.

You can put one in the discharge line because that is not a suction line.

There is a drawing on the Jabsco website that shows this. Unfortunately I can't get on their site right now or I'd post it for you.

Michael, cover the vent with a piece of tape, I bet the whistle goes away and you can draw raw water again. Then move the vent to the correct location.
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Old 19-07-2014, 21:56   #13
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Re: Vented loop to head whistles

Thanks HopCar,
Yes I conceed that you and Sail Monkey are correct. Had trouble with this one since I bought the boat with the loop in the suction line and thought it had been installed correctly. Last week made the change putting the loop in the line between the pump and the head and all is much improved. Had to drill a couple of new holes to reroute the hoses and in about 30 min had it done. Easier than I expected. Thanks for being persistent with a stubborn old sailer.

Michael
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Old 19-07-2014, 23:36   #14
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Re: Vented loop to head whistles

Don't most marine toilets have the pump attached to the head? There is no hose between the pump and bowl, so how can you put a siphon break there?

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Old 20-07-2014, 06:50   #15
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Re: Vented loop to head whistles

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Don't most marine toilets have the pump attached to the head? There is no hose between the pump and bowl, so how can you put a siphon break there?

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99.9% of manual marine heads have a hose from the pump to the backside of the bowl to supply flush water. I'll admit that I don't have a lot of experience with electric heads, but would bet they're similar.
Heads that were intended to be freshwater flush may not have this hose.
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