Heads anti syphon loops

crown22

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Have followed the instructions supplied with my new toilet and fitted anti syphon loops because my bowl is probably below the water line when stationary and will definitely be when on starboard tack.Use the head for the first time after lifting in and I thought I saw some water spray out of
one or both of the loops.Remember reading on the forum that this can happen so am a bit confused about why these things are sold and recommended.Thanks
 

RupertW

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I’m interested in this too. I have an equivalent to an anti siphon break on the outlet side as the holding tank has a breathing tube just below the toe rail but nothing on the input side even though the bowl is just below sea level but has never flowed in unlike the sink outlet which needs to be shut off when heeling.
 

lw395

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Have followed the instructions supplied with my new toilet and fitted anti syphon loops because my bowl is probably below the water line when stationary and will definitely be when on starboard tack.Use the head for the first time after lifting in and I thought I saw some water spray out of
one or both of the loops.Remember reading on the forum that this can happen so am a bit confused about why these things are sold and recommended.Thanks

Those anti-syphon valves are supposed to only let air in, to break the syphon.
They should not allow air, let alone 'water' out.
 

VicS

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Have followed the instructions supplied with my new toilet and fitted anti syphon loops because my bowl is probably below the water line when stationary and will definitely be when on starboard tack.Use the head for the first time after lifting in and I thought I saw some water spray out of
one or both of the loops.Remember reading on the forum that this can happen so am a bit confused about why these things are sold and recommended.Thanks

I’m interested in this too. I have an equivalent to an anti siphon break on the outlet side as the holding tank has a breathing tube just below the toe rail but nothing on the input side even though the bowl is just below sea level but has never flowed in unlike the sink outlet which needs to be shut off when heeling.

The purpose of the vented loop is to eliminate the possibility of water continuing to flow in, over flow the toilet and flood the boat. The vent valve allows air to enter in order to break the siphoning which could occur with an unvented loop

The discharge probably has a joker valve. These may stop back flow when new but probably wont when not so new. A Jabsco "twist and lock" type of pump holds the bottom valve shut but by all accounts is not perfect.

On the inlet side the little valves in the pump head of a Jabsco type toilet will hold back a small head pressure but they are not intended for this purpose hence the vented loop.

Loadsa videos about Jabsco toilets and other stuff here https://www.xylem.com/en-us/brands/jabsco/videos/
 

Humblebee

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I recently re-piped and generally overhauled the Lavac in our boat recently (See threads re unhappiness cleaning pump). Anyway, the job, when done, with loops in the inlet and outlet hoses left us with too much water in the bowl, near to overflowing in fact. Not keen on valves in the output side of things but drilled a tiny (2.5mm) hole in the top of the inlet pipe. Bowl now fills to correct level and vacuum breaks down in a coupe of minutes so lid can be lifted, bowl cleaned etc.
Small hole in inlet pipe to start with is my advice. Can be bound shut with self amalgamating tape if you change your mind.
 

VicS

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I recently re-piped and generally overhauled the Lavac in our boat recently (See threads re unhappiness cleaning pump). Anyway, the job, when done, with loops in the inlet and outlet hoses left us with too much water in the bowl, near to overflowing in fact. Not keen on valves in the output side of things but drilled a tiny (2.5mm) hole in the top of the inlet pipe. Bowl now fills to correct level and vacuum breaks down in a coupe of minutes so lid can be lifted, bowl cleaned etc.
Small hole in inlet pipe to start with is my advice. Can be bound shut with self amalgamating tape if you change your mind.

The small vent hole in the inlet to a Lavac is a key part of the way Lavacs work. They are normally supplied with two inserts, drilled with different sized holes, that fit in the inlet pipe at its highest point, choosing which one leaves the require amount of water in the bowl. You have only discovered what reading the Lavac user guide would have told you! http://www.blakes-lavac-taylors.co.uk/pdf/lavac.pdf

With a Jabsco the loop normally replaces the short length of hose between the pump and the bowl. but a loop between the seacock and the pump with a very small hole at its highest point might work but if the hole is too big it'll just suck air in and not flush the toilet properly. A hole in the loop in its normal location will just produce a little fountain of water !
 
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johnalison

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A hole in the loop in its normal location will just produce a little fountain of water !

Maybe if you drilled a very small hole at an angle it might just possible act as a valve and close itself under pressure. Or more likely not.
 

VicS

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Maybe if you drilled a very small hole at an angle it might just possible act as a valve and close itself under pressure. Or more likely not.

More likely not but if you angle it towards the user . you will know to cover the hole with a finger but get endless amusement from others getting soaked ... especially if they think it might be effluent
 

kacecar

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I had a similar problem when I fitted a new toilet. The old toilet installation didn't feature any anti-syphon loops but the instructions for the fitting of my new, different type of toilet suggested they were essential. Consequently I fitted loops on both the input and outlet pipes, both with fairly cheap anti-syphon valves - a type where a small rubber valve is held in place at the top of the loop by a threaded plastic cap. I found that if the cap was over tightened then the rubber valve could become distorted and allow small quantities of fluid to leak out while the toilet was being pumped. Loosening the cap fitting very slightly removed the leakage problem.
 

Yngmar

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The purpose of the vented loop is to eliminate the possibility of water continuing to flow in, over flow the toilet and flood the boat. The vent valve allows air to enter in order to break the siphoning which could occur with an unvented loop

The discharge probably has a joker valve. These may stop back flow when new but probably wont when not so new. A Jabsco "twist and lock" type of pump holds the bottom valve shut but by all accounts is not perfect.

I've just sorted through the plumbing spares box a few days ago and it had a Forespar vented loop - with the tiny rubber duckbill valve cracked. That would cause the symptoms described by the OP. Forespar sells spares, indicating that this failure is not uncommon.
 
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