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  1. #1
    Join Date
    Jul 2004
    Location
    Manchester
    Posts
    146

    Default Heads anti syphon loops

    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

  2. #2
    Join Date
    Feb 2007
    Location
    Essex
    Posts
    21,556

    Default Re: Heads anti syphon loops

    Never had any trouble with mine. Maybe the cap isn't screwed down fully.
    Far away is near at hand in images of elsewhere

  3. #3
    Join Date
    Mar 2002
    Location
    Greenwich
    Posts
    7,160

    Default Re: Heads anti syphon loops

    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.

  4. #4
    Join Date
    May 2007
    Posts
    35,832

    Default Re: Heads anti syphon loops

    Quote Originally Posted by crown22 View Post
    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.

  5. #5
    Join Date
    Jul 2002
    Location
    Home: Kent. Boat: Chichester
    Posts
    43,072

    Default Re: Heads anti syphon loops

    Quote Originally Posted by crown22 View Post
    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
    Quote Originally Posted by RupertW View Post
    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/

  6. #6
    Join Date
    Nov 2001
    Location
    Muchalls
    Posts
    1,202

    Default Re: Heads anti syphon loops

    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.

  7. #7
    Join Date
    Jul 2002
    Location
    Home: Kent. Boat: Chichester
    Posts
    43,072

    Default Re: Heads anti syphon loops

    Quote Originally Posted by Humblebee View Post
    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 !
    Last edited by VicS; 11-04-19 at 19:02.

  8. #8
    Join Date
    Feb 2007
    Location
    Essex
    Posts
    21,556

    Default Re: Heads anti syphon loops

    Quote Originally Posted by VicS View Post
    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.
    Far away is near at hand in images of elsewhere

  9. #9
    Join Date
    Jul 2002
    Location
    Home: Kent. Boat: Chichester
    Posts
    43,072

    Default Re: Heads anti syphon loops

    Quote Originally Posted by johnalison View Post
    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

  10. #10
    Join Date
    Oct 2007
    Location
    UK
    Posts
    152

    Default Re: Heads anti syphon loops

    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.

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