Exhaust anti-syphon options

[Graham_Wright]

What is the best way of designing an effective safe solution?

I don't really like the idea of a constant dribble into the cockpit.

Is there any mileage in a non return valve - allows sucking but not blowing.

Is it possible to utilise a bleed off that discharges sufficiently high so that the column required to discharge is greater than the equivalent from the exhaust system back pressure?

 

[Tranona]

Very easy. Vetus (and others) make an ant-syphon valve which does not dribble, but does need cleaning regularly. There is good information including schematic installation diagrams in their catalogue www.vetus.com

 

[boatmike]

Very easy. Vetus (and others) make an ant-syphon valve which does not dribble, but does need cleaning regularly. There is good information including schematic installation diagrams in their catalogue www.vetus.com

Yes and if you don't clean the valve regularly it jams and can end up with catastrophic engine failure. I would rather use the other version with no valve but a very small pee hole to a skin fitting. You can always ensure it works that way. Steady pee OK. No pee and it's blocked. Simples!

 

[VicS]

You'll get used to it and eventually find that you dont have to keep going for a pee yourself.

If you really dont want the antisyphon valve peeing into a cockpit drain then as suggested above fit a type with a valve, but be aware that it might block or fail to open. Alternatively route the discharge overboard as also shown in the Vetus catalog pages 78 and 79

 

[Pye_End]

I have used a valve type (Halyard rather than Vetus) for 18 years and have never found it blocked. It has been stripped and cleaned once or twice (no more), but out of interest rather than necessity. Following the above posts is this lucky or normal?

 

[prv]

I have used a valve type (Halyard rather than Vetus) for 18 years and have never found it blocked. It has been stripped and cleaned once or twice (no more), but out of interest rather than necessity. Following the above posts is this lucky or normal?

I would say that the majority of boats (particularly AWBs) have valve-type rather than pee-type antisiphons. I base this on never having knowingly chartered a boat with a dribble pipe.

Since the place isn't full of sunken Bavarien and Beneteaux, I can only conclude that blockage is a relatively rare event.

Pete

 

[Tranona]

I have used a valve type (Halyard rather than Vetus) for 18 years and have never found it blocked. It has been stripped and cleaned once or twice (no more), but out of interest rather than necessity. Following the above posts is this lucky or normal?

Yes I have had a Vetus valve for at least 15 years and probably checked it twice. Just stripped a Volvo valve that I know has not been touched for 4 years. Was still clear. The vetus ones in particular are very easy to check, so no excuse.

 

[Graham_Wright]

Very easy. Vetus (and others) make an ant-syphon valve which does not dribble, but does need cleaning regularly. There is good information including schematic installation diagrams in their catalogue www.vetus.com

Thanks for the steer.

I looked at the Vetus recommendations and am appalled at the comparison between their recommended loop height and what Mr Norris supplied. His was no more than 6"!

O.k., it was above the waterline but not by much.

The loop will reach the deckhead tonight.

Interestingly, the spell checker accepted hight instead of height! New word to me or is it our erudite American cousins spelling?

Addendum OED;- called, named - Middle English.

You learn something every day. (Apologies to the Americans!).

 

[snooks]

It should be as high as possible as close to the centreline as possible

(I've just fitted one and read the destructions)

 

[alahol2]

Mine pees out of the transom alongside the exhaust. Two pees good, one pee bad.

PS Dinghy blown under transom, bad.

 

[maxi]

Have a chat with Aquafax, they do (did) sell a small ball-type anti-syphon device at approx £5, which is simple and effective, about the size of a cigarette lighter.

Can't see it in their current catalogue but they may be able to help as the item is not exclusively Aquafax.

I have had one fitted for several years now, no problems and no dribbles!

 

[vyv_cox]

Mine pees to a nozzle on the trap. Has been like that since the new engine was fitted in 2001.

 

[aitchem]

I got one of these from T A Norris
I have a basic distrust of moulded plastic things
having been involved in plastics design ( automotive )

 

[Graham_Wright]

I got one of these from T A Norris
I have a basic distrust of moulded plastic things
having been involved in plastics design ( automotive )

Your post implies this is a "moulded plastic thing" (and I agree with your sentiment).

But the Norris website declares it to be "all metal".

But then, knowing Norris, it is probably brass.

 

[prv]

Your post implies this is a "moulded plastic thing" (and I agree with your sentiment).

Um, no, it implies it isn't a moulded plastic thing, hence why he chose it.

Pete

 

[alahol2]

Um, no, it implies it isn't a moulded plastic thing, hence why he chose it.

Pete

Mind you, the rest of his boat is a 'moulded plastic thing'.

 

[Ruffles]

Yes I have had a Vetus valve for at least 15 years and probably checked it twice. Just stripped a Volvo valve that I know has not been touched for 4 years. Was still clear. The vetus ones in particular are very easy to check, so no excuse.

I have a short pipe on the outlet clipped to the side of the engine bay. Makes it easy to test. Should be able to blow into it with no resistance but not suck.
It also makes a pleasant farting noise shortly after the engine is turned off !!!