Anti Syphon valve – or valves?

[FinesseChris]

Morning all,

Am planning a new engine (Beta 16, probably) in place of the tired, old, poorly marinised, leaky, overheating Kubota in our Finesse 24.

Looking at the ancillaries, I've got thoroughly confused about anti-syphon loops.

When I bought the boat the surveyor commented on the lack of an anti-syphon loop so the vendor had one fitted – on the inlet side.

The piping runs raw water inlet – pump – up to Vetus valve in cockpit locker – back to heat exchanger.

Eleven years on (and a lot of reading of various authorities) and I am still not quite sure what this does.

I am however convinced that I need what I have not got, which is a syphon loop between exhaust bend and waterlock.

My question: do I need both?

Cheers

Chris

 

[Tranona]

No. The normal place for it is in the hose between the heat exchanger output and the injection point into the exhaust. Sometimes it is put on the inlet because there is no external hose on the outlet. There is on the Nanni and the Beta. The latter is a bit easier to instal the valve correctly because the pipe is quite long - you need to take the L shaped pipe off and replace it with a run of plain pipe through the valve. The Nanni is a bit more tricky as the hose is quite short and the ends are different sizes - but still do-able.

For more information on valves and installation there are schematics in the vetus catalogue www.vetus.com

 

[PetiteFleur]

I started with a Vetus anti-syphon valve but it's difficult to clean so chucked th valve bit in the bin and ran a small diameter hose(6mm? ) to the transom. Easy to see if the valve is worked as when motoring it 'pees' quite nicely, dribbling when idling. Some people take the hose to the cockpit so one can see it 'peeing', but I prefer a dry cockpit.

 

[jonathanhsm]

Anti syphon piddle tube

My Vetus also blocked on a couple of occasions flooding cylinder with seawater. Not good. So I too chucked it away and now piddle into the cockpit - but it goes straight down the cockpit drain so no wet patch!

 

[VicS]

Morning all,

Am planning a new engine (Beta 16, probably) in place of the tired, old, poorly marinised, leaky, overheating Kubota in our Finesse 24.

Looking at the ancillaries, I've got thoroughly confused about anti-syphon loops.

When I bought the boat the surveyor commented on the lack of an anti-syphon loop so the vendor had one fitted – on the inlet side.

The piping runs raw water inlet – pump – up to Vetus valve in cockpit locker – back to heat exchanger.

Eleven years on (and a lot of reading of various authorities) and I am still not quite sure what this does.

I am however convinced that I need what I have not got, which is a syphon loop between exhaust bend and waterlock.

My question: do I need both?

Cheers

Chris

What you have is satisfactory and with some engines it is the only practical way of doing it. You do not also need one between the heat exhanger outlet and the injection point.

the antisyphon valve is necessary if the injection point into the exhaust is not substantially above the water line ... Vetus recommend 15 cm minimum.

The antisyphon valve should located well above the waterline ... Vetus recommend 40 cm minimum.

You have a choice between a device with a valve... which must be checked periodically for correct operation ... and a device without a valve which discharges a small "pee stream" overboard or into a cockpit drain.

The one place in the system which is unsuitable for the location of the antisyphon device is between the water inlet and the water pump as it would simply allow air to be sucked in by the pump!

 

[pappaecho]

If you are unsure you can conduct a simple test.

Seal off the anti siphon valve.
Disconnect the output from the heat exchanger and tie it at the same level as the spigot from which it is removed.

Switch on the inlet sea cock, and observe the output pipe. If it drips ( give it some time) the system is siphoning and if put back would firstly fill the exhaust system and then the engine sump via the exhaust valves.

If you unclamp the antisphon valve the dripping should stop, indicating that it is working

 

[pappaecho]

Oops sorry. I mean disconnect the output from the heat exchanger to the exhaust elbow

 

[VicS]

I hate that "only practical way" bit. Some 'yachty' installations are a joke, compared with proper practice. 15 cm - where is your waterline when close-hauled in strong winds?
I guess you're talking about something like this: http://www.northern-lights.com/PDFs/misc_pdfs/dont_drown_me.pdf

Have seen (well, had to work on them on the way ) engines filled with water. One for example had exhaust going about level (with vetus silencer in bilge btw) so water just run up exhaust on stormy passage - antisiphon loop was irrelevant (there were two). Another - water injected in exhaust without much loop in exhaust first. Antisiphon on inlet.

What you need is exhaust going upwards in the loop (riser) as high as can get (mine is up deck) - conservative estimate was "above water at any possible angle of heel"; and water pipe the same, with a means of syphon-breaking, not necessarily valve... then injection point in exhaust put much lower (as possible) after it's loop. This way water has little possibility to get back to engine. Theoretically, when the exhaust makes high enough loop and injection point is low afterwards, antisiphon valve is not necessary. (Don't take this for granted).

Today they put exhaust (without any riser!) down into the bilge, which means it can fill with water... kill me, but I can not understand why It would be OK if must be, with waterlocking silencer etc, but after a riser!
The story goes that without antosiphon water will continue to flow after engine is stopped, and can fill the exhaust, then cylinders. Yes, true, but with exhaust that can be flooded - it can fill with seawater from other end...

Don't forget valve on exhaust outlet then. Flapper valve is better - maybe not so efficient in stopping water, but works all the time, while not many people will close manual one...

Antisiphon on inlet is not necessary, as there is impeller in pump acting a bit like valve blocking the way. But. On some wide a***ed new boat, while she was slamming in heavy sea, water entered engine probably this way - maybe there was enough pressure in the inlet to push through.
Some peple prefer to have one, and a strainer above waterline too...

"Only practical way" meaning that the anti-syphon loop etc must be fitted between the water pump discharge and the inlet to the engine or heat exchanger on some engines because it is not practical or perhaps not even possible to divert the outlet flow.
This applies to some of the Volvo Penta engines in common use. Maybe also to the OP's existing engine but not to a Beta 16.

Water line should I agree be the heeled water line.

A riser or swan neck in the exhaust pipe after the water trap etc is another issue... just as important I agree .. but was not the subject of the original question.

You CANNOT rely on the water pump impeller vanes effectively stopping water flowing in. Maybe it will when it is brand new but not once it gets a bit worn. Hence the need for raised loop with a syphon breaking device of one sort or the other positioned somewhere in the system between the pump discharge and the injection point.... before or after the heat exchanger, which ever is possible or merely convenient.


Retuning to the Beta 16 . The antisyphon loop and valve would normally replace the black hose between the heat exchanger outlet and the exhaust injection pont.

 

[Tranona]

I hate that "only practical way" bit. Some 'yachty' installations are a joke, compared with proper practice. 15 cm - where is your waterline when close-hauled in strong winds?
I guess you're talking about something like this: http://www.northern-lights.com/PDFs/misc_pdfs/dont_drown_me.pdf

Have seen (well, had to work on them on the way ) engines filled with water. One for example had exhaust going about level (with vetus silencer in bilge btw) so water just run up exhaust on stormy passage - antisiphon loop was irrelevant (there were two). Another - water injected in exhaust without much loop in exhaust first. Antisiphon on inlet.

What you need is exhaust going upwards in the loop (riser) as high as can get (mine is up deck) - conservative estimate was "above water at any possible angle of heel"; and water pipe the same, with a means of syphon-breaking, not necessarily valve... then injection point in exhaust put much lower (as possible) after it's loop. This way water has little possibility to get back to engine. Theoretically, when the exhaust makes high enough loop and injection point is low afterwards, antisiphon valve is not necessary. (Don't take this for granted).

Today they put exhaust (without any riser!) down into the bilge, which means it can fill with water... kill me, but I can not understand why It would be OK if must be, with waterlocking silencer etc, but after a riser!
The story goes that without antosiphon water will continue to flow after engine is stopped, and can fill the exhaust, then cylinders. Yes, true, but with exhaust that can be flooded - it can fill with seawater from other end...

Don't forget valve on exhaust outlet then. Flapper valve is better - maybe not so efficient in stopping water, but works all the time, while not many people will close manual one...

Antisiphon on inlet is not necessary unless the engine is below water, as there is impeller in pump acting a bit like valve blocking the way. But. On some wide a***ed new boat, while she was slamming in heavy sea, water entered engine probably this way - there was enough pressure in the inlet to push through.
Some people prefer to have one, and a strainer above waterline too...

You are just confusing things here. The Vetus schematic referred to earlier gives the required information. The purpose of the anti syphon valve and the swan neck are different. The anti syphon as its name implies breaks the syphon when the engine is stopped to prevent water being drawn in from the water trap. The swan neck before the exhaust outlet is to prevent water flooding back through the exhaust.

Placing the valve where VicS indicates and taking it above the waterline is simple and effective - then the only choice is whether you have a closed valve - ie one that only opens when the engine stops or an open valve venting a continuous stream overboard. The latter are arguably safer, but not always possible or suitable to install - for example if, like my boat the cockpit does not self drain.

 

[VicS]

Therefore worth noting that if the engine is placed low, underwater or almost, it's good idea to have an antisiphon before the pump. Water just can be pushed into the system in the seaway, bit by bit, and once it gets to the engine it can go over the loop on the back into the exhaust , especially when there is little height (antisiphon on that loop is no help as water is pushed up anyway, it's only the high level of the loop that matters maybe - or maybe not).

No you cannot put the anti-syphon valve before the pump!

If you do air will be sucked in!

Positioning the anti-syphon loop high enough ( Vetus recommend a minimum of 40cm above the WL) will prevent water being forced in in a seaway.

 

[VicS]

"Positioning the anti-syphon loop high enough ( Vetus recommend a minimum of 40cm above the WL) will prevent water being forced in in a seaway." Yes - if we are talking about loop before engine.
With loop after the engine - do you always believe what's written in manufacturer's handbook? High enough... that's it.

It makes no difference if the anti-syphon loop is located between the pump and the engine (or heat exchanger) or if it is located between the engine (or heat exchanger) and the exhaust. If it is high enough it will prevent water being forced over the loop and into the exhaust!

The pump vanes will effectively stop large amounts of water being forced over quickly anyway ... they just cannot be relied upon to prevent a slow trickle if there is no anti-syphon device.

The picture of the Beta engine shows how easy it is to fit an anti-syphon loop and valve between the heat exchanger outlet and the exhaust on that engine.

The heat exchanger outlet on the VP MD2010/20/30/40 series engines, on the other hand, is connected directly to the exhaust injection point. On those the hose between the water pump and the heat exchanger inlet is easily replaced by the anti-syphon loop.

 

[VicS]

But then again - will add one:

Such a valve - before the pump - was standard on propulsion plant complete, that was made for fishing vessel here on Baltic time ago. Some also went into big steel yachts produced here. On one I have crewed lately for trip Poland - Greenland - Yan Mayen - Norway - and back, so got aquainted with the machine which gave some trouble, being old. Valve was working OK.

So no reason to be so "!" sure - there is more than one way to skin a cat...

So how do you stop air being sucked in if it is before the pump?

Maybe a whacking great pump on fishing boat will handle a small amount of air in-leakage but the performance of the little flexible vane pumps on yacht engines will almost certainly suffer with engine overheating being a likely consequence.

An antisyphon valve, if one is required, can go almost anywhere in the system between pump and final injection into the exhaust without causing any problems.
It would be very inadvisable to put it on the suction side of the pump where it very likely will cause problems so why do it?

 

[VicS]

Valve was closing with pump working, from suction I would guess?

Anti-syphon valves open when under suction. That is how they function to break the syphon.

 

[VicS]

"They function" ?
All valves in the world? each and every one on them, you mean?
Ok, those typical on boats, made by Vetus and so on. In typical design of engine installation.

You can say also that every exhaust system is waterlocking and down in the bilges - which is the original cause of problems and reason why antisiphons are so important

Did I mention I advocate another approach ?
Seems that part nobody even try to notice the meritum, so as said - this is pointless discussion about irrelevant details.

Good night.

We are talking about the type of anti-syphon valves fitted to the cooling water system of small boat engines....that was the original subject of the thread... and yes Vetus ones are typical of what we are talking about.