Syphon Break position in system?

[rjcoles]

I have been scratching my head about this problem so I thought I'd ask you lot to help.

I am installing a new (secondhand) engine, a Perkins M92 and the water injection point is a couple inches above the static waterline. The engine has short pipe between the exhaust elbow and the heat exchanger, so breaking into the circuit at that point is not easy. Just after the Jabsco pump there is a water take-off to supply the shaft seal. My thought is to have the syphon break in this tube between the engine and the seal. I hope that this will kill two birds with one syphon break in that it will stop water back feeding from the stern tube and also act as the syphon break for the engine.

For additional info the exhaust goes from the engine to a water-lock and then vertically up to a Halyard water separator.

Whats the forums view?

 

[VicS]

If the water injection point is less than about 15cm above the water line a syphon break should be fitted.

The common location is in the pipe leading to the exhaust elbow.

If this is not possible the pipe between pump and engine/heat exchanger can be used

It must not be fitted anywhere on the suction side of the pump or it will suck in air while running.

The pipe from pump to heat exchanger must be routed up to the antisyphon valve and down again.
Your suggestion will not be effective in breaking the syphon if I understand it correctly.

Connecting the feed for the shaft seal to the system between pump and antisyphon valve will prevent water feeding into the exhaust system from the stern tube.

The syphon break should be at least 40 cm above the waterline

 

[lenseman]

Following on from VicS, I have just bought one to fit and it states 20cm but the rubber valve at the top of the invert has not been manufactured correctly and I warned the shop (YouBoat) and they were all the same.

The small slit in the flattened part of the valve was not cut and therefore could not work. It was easy enough to cut to make work.

 

[chewi]

The common location is in the pipe leading to the exhaust elbow.

Mine leads the antisyphon vent into the top of a cockpit drain, just below the cockpit floor.
When running I can check the cooling water telltale and even poke my mk1 finger in it to check the temp.

When not running the same tube acts as the vent.
Simplicity itself, no hanging over the transom to check the coolant.

 

[ghostlymoron]

Mine discharges through the side of the boat and is easy to see but it does tend to fill up the dinghy if tied up in the wrong place.

 

[sailorman]

I have been scratching my head about this problem so I thought I'd ask you lot to help.

I am installing a new (secondhand) engine, a Perkins M92 and the water injection point is a couple inches above the static waterline. The engine has short pipe between the exhaust elbow and the heat exchanger, so breaking into the circuit at that point is not easy. Just after the Jabsco pump there is a water take-off to supply the shaft seal. My thought is to have the syphon break in this tube between the engine and the seal. I hope that this will kill two birds with one syphon break in that it will stop water back feeding from the stern tube and also act as the syphon break for the engine.

For additional info the exhaust goes from the engine to a water-lock and then vertically up to a Halyard water separator.

Whats the forums view?

i fitted my syphon break between the sea water pump & the H.E. & it "piddles" into the cockpit drain.
it doesnt matter where the vac. break is in the system ( i can see if there is a blockage too ) as long as it works.
the piddler is some 300m/m above the engine on a long loop so far its done 900 hrs