Syphon Breaker on Raw Water side intake side of MD 2040 (Beneteau 373) ?

[Kinsale373]

I was surprised to find that my Bene 373 has a Syphon breaker situated on the Raw Water intake line . The salt water line from the inlet seacock goes up to a breaker just above the front of the engine and then on the the salt water pump. ( The small tube from the top of the swan neck goes into the bilges!) From here water is pumped through the heat exchanger and out to the exhaust. I thought that they should be situated on the exhaust side with the water cooler outllet pumped up to the swan neck and then back down to the exhaust manifold? Maybe its effectively the same thing? Anyone any ideas?

Regards, Kinsale 373

 

[johnalison]

A syphon break on the inlet is normal, to prevent the boat sinking with a leak in that section. The exhaust is a different matter and would normally have its own loop. Some inlet syphon breaks have a rubber diaphragm that needs regular servicing.

 

[duncan99210]

Mine is between the raw water pumps and the heat exchanger. The installation manual shows it as being mounted like that or between the heat exchanger and the exhaust elbow. Seeing as the purpose of the valve is to break the syphon effect leading to back flooding from the exhaust, it doesn't make much difference where it's located, so long as there is one present.

 

[CCJ]

I was surprised to find that my Bene 373 has a Syphon breaker situated on the Raw Water intake line . The salt water line from the inlet seacock goes up to a breaker just above the front of the engine and then on the the salt water pump. ( The small tube from the top of the swan neck goes into the bilges!) From here water is pumped through the heat exchanger and out to the exhaust. I thought that they should be situated on the exhaust side with the water cooler outllet pumped up to the swan neck and then back down to the exhaust manifold? Maybe its effectively the same thing? Anyone any ideas?

Regards, Kinsale 373

mine between raw pump & HE i have it piddling into a cockpit drain so i can get an early indicator of a blockage, it has worked faultlessly for 14 years & some 1400 hrs

 

[VicS]

I was surprised to find that my Bene 373 has a Syphon breaker situated on the Raw Water intake line . The salt water line from the inlet seacock goes up to a breaker just above the front of the engine and then on the the salt water pump. ( The small tube from the top of the swan neck goes into the bilges!) From here water is pumped through the heat exchanger and out to the exhaust. I thought that they should be situated on the exhaust side with the water cooler outllet pumped up to the swan neck and then back down to the exhaust manifold? Maybe its effectively the same thing? Anyone any ideas?

Regards, Kinsale 373

It is not practical to fit a syphon break between the HE and the exhaust on a MD2040. One is connected more or less directly to the other surely?


Therefoe the syphon break goes between the raw water pump discharge and the inlet to the HE.

It MUST NOT go where you seem to describe, between the water intake seacock and the pump suction.......... The pump will suck air in through it it is and you will get little or no water being pumped through

 

[macd]

I thought that they should be situated on the exhaust side with the water cooler outllet pumped up to the swan neck and then back down to the exhaust manifold? Maybe its effectively the same thing? Anyone any ideas?

The syphon break is to prevent sea water from the inlet side flooding the engine when it's not running. To that extent, the break will work if fitted anywhere between seawater inlet and exhaust mixing point (which is effectively one long closed pipe). However, for the reasons Vic describes, it must not be fitted upstream of the pump since it inhibits the pump from priming. (If your set-up currently overcomes this, you can be happy your pump works so well, but it will do so less ably as the pump's impeller and faces wear.)

 

[Kinsale373]

Hi Johnalison Thats the bit I don't understand. How does a Syphon breaker protect against leaks in the inlet.. If there is a leak in the line to the pump how will the syphon breaker help this?
Regards Kinsal e 373

 

[macd]

Hi Johnalison Thats the bit I don't understand. How does a Syphon breaker protect against leaks in the inlet.. If there is a leak in the line to the pump how will the syphon breaker help this?
Regards Kinsal e 373

Unless the inlet seacock is closed there's always a 'leak'. (The pump itself acts to some extent to prevent water ingress when stationary, but not reliably, particularly as it wears.)

 

[Kinsale373]

Helo Vic,
Agreed, If its set up with the Rubber End cap feeding directly into the Exhaust manifold it would not work. I was thinking though, that if I rotated the end cap by say 45 Deg ( Disconnect the feeder tube to the exhaust manifold , I could then plum the outlet from the heat exchanger End cap up to a new Syphon breaker and back down to the Exhaust manifold. Wouldnt be too difficult. I'm try to fully understand the current set up before I modify.
I take you pointabout drawing in some air, if what I say is correct. It would only be throught small vacuum breaker hole though, so I dont think this would interfere much with the pump performance. I am going back to the boat today and I will re check my statements on current layout!

Thanks for your input , Kinsale 373

 

[macd]

I take you pointabout drawing in some air, if what I say is correct. It would only be throught small vacuum breaker hole though, so I dont think this would interfere much with the pump performance.

As I wrote earlier, just because the pump can currently overcome the existing syphon break, doesn't mean it will always do so. All manner of things...wear in the pump, damage to the impellor, partial clogging of the inlet strainer...will sooner or later render it unable to prime. Every authoritative source you can find will tell you your break's in the wrong place.

 

[duncan99210]

The syphon break valve is not there to prevent a 'leak': it's there to prevent cooling water being sucked back into the engine from the wet exhaust. Without the valve there is a danger that the contents of the exhaust piping, when the engine is turned off, will be sucked back into the exhaust manifold and cause a waterlocked engine. It doesn't matter where the break is, so long as it prevents this happening.
Any damage to the pipe work will lead to sea water entering the boat: the protection against this is to close the engine sea cock.

 

[VicS]

Helo Vic,
Agreed, If its set up with the Rubber End cap feeding directly into the Exhaust manifold it would not work. I was thinking though, that if I rotated the end cap by say 45 Deg ( Disconnect the feeder tube to the exhaust manifold , I could then plum the outlet from the heat exchanger End cap up to a new Syphon breaker and back down to the Exhaust manifold. Wouldnt be too difficult. I'm try to fully understand the current set up before I modify.
I take you pointabout drawing in some air, if what I say is correct. It would only be throught small vacuum breaker hole though, so I dont think this would interfere much with the pump performance. I am going back to the boat today and I will re check my statements on current layout!

Thanks for your input , Kinsale 373

The correct place for the siphon break on the MD 20x0 series engines is between the pump discharge and the HE inlet. There is no advantage in it being between the HE and the exhaust inlet so nothing to be gained by attempting to fit it there.

It merely has to be at a high point , well above the waterline ( Vetus recommend 40cm minimum, Beta suggest 50cm ) .somehwere in the circuit so that when the engine stops air enters to break the siphon.

Leave in in the pump suction if you must but when you have pump priming, cooling or waterflow problems, as you surely will, you will know where to look for the cause .


This is the VP part (21662702 and the connecting hoses to fit it between pump and HE

 

[Kinsale373]

Your point about the circuit being one long pipe makes sense. Also the point about the bleed pipe on the syphon breaker subtracting from the pump efficiency. I'm going back to the boat this morning to check by appraisal of the current plumbing !

So a syphon breaker inserted anywhere from the +Ve side of the bump to through the exhaust manifold will do the job. That's making sense to me ok.
Thanks Mac , Regards, Kinsale 373

 

[macd]

The syphon break valve is not there to prevent a 'leak': it's there to prevent cooling water being sucked back into the engine from the wet exhaust. Without the valve there is a danger that the contents of the exhaust piping, when the engine is turned off, will be sucked back into the exhaust manifold and cause a waterlocked engine.

That's incorrect. The exhaust has it's own arrangements to prevent back-filling. The syphon break is there to break the closed pipe from inlet seacock to mixing elbow from allowing water to enter the cylinders (usually after first filling the exhaust and its watertrap).

 

[duncan99210]

That's incorrect. The exhaust has it's own arrangements to prevent back-filling. The syphon break is there to break the closed pipe from inlet seacock to mixing elbow from allowing water to enter the cylinders (usually after first filling the exhaust and its watertrap).

The exhaust, if fitted in accordance with the Volvo instructions will have a silencer/water trap. The idea of the water trap is that it is sized so as to be able to contain most (if not all) the water in the exhaust. In theory, this should be sufficient to prevent a syphon action being established, as it breaks the filled pipe. However, there's always the effect of a healed boat etc to consider. So to break the syphon, you need a valve somewhere in the system. One break somewhere along the pipework is all that is required. Or am I missing something?

 

[Kinsale373]

The though just occurred to me that Beneteau might have made the decision to put it in the Low pressure side of the pump so that they did not have to deal with a constant piddle of water coming out of the syphon breaking line, less plumbing for them ! Anyway, for the momment Ill take Vics advise and leave well enough alone , I'm going to re check my statement on how exactly it is plumbed in relative to the pump.

Ill let you all know.

Thanks everyone for the inputs and ideas , Regards, Kinsale 373

 

[VicS]

The exhaust, if fitted in accordance with the Volvo instructions will have a silencer/water trap. The idea of the water trap is that it is sized so as to be able to contain most (if not all) the water in the exhaust. In theory, this should be sufficient to prevent a syphon action being established, as it breaks the filled pipe. However, there's always the effect of a healed boat etc to consider. So to break the syphon, you need a valve somewhere in the system. One break somewhere along the pipework is all that is required. Or am I missing something?

The water trap in the exhaust is there to safely hold all the water remaining in the exhaust system when the engine is stopped.
It does nothing to break the siphon which will exist between the inlet sea-cock and the injection point if the injection point is below or even close to the water line. True the trap will collect water siphoning in initially but once full the water can overflow into the engine via an exhaust valve.
The antisiphon valve ( or vacuum valve as VP call it) will allow air to enter to break this siphon as soon as the engine is stopped.

 

[macd]

Or am I missing something?

Possibly, or perhaps you just weren't very clear. Anyway, Vic kindly saved us the trouble of clearing it up.

 

[cmedsailor]

I was surprised to find that my Bene 373 has a Syphon breaker situated on the Raw Water intake line . The salt water line from the inlet seacock goes up to a breaker just above the front of the engine and then on the the salt water pump. ( The small tube from the top of the swan neck goes into the bilges!) From here water is pumped through the heat exchanger and out to the exhaust. I thought that they should be situated on the exhaust side with the water cooler outllet pumped up to the swan neck and then back down to the exhaust manifold? Maybe its effectively the same thing? Anyone any ideas?

Regards, Kinsale 373

That is strange, because my Beneteau 361 (with the MD2030 engine) which is the boat that Beneteau 373 has replaced, similar to what other people mentioned has the vetus syphon break after the pump and before the heat exchanger.

 

[Kinsale373]

To conclude,
I re checked my set up this afternoon. I was wrong first time! The raw water comes in through strainer , on through the Reverse Forward box and then on to the Pump. From the pump it goes up to the Syphon Breaker and onto the Heat exchanger . I guess ,but I must I must look a little closer to see if I have a Syphon breaker with a small valve to prevent continuous peeing out of water due to pump pressure. Anyway it looks like my set up is as described by a few contributers. I've learned a bit about Syphon breakers and my cooling system so thanks to everyone for inputs .

Regards, Kinsale 373