Siphon break – hose size for tell tale

[ricardio]

I have an old Vetus siphon break with a valve that is now beyond redemption. It is an old version which has a ½” BSP thread at the top of the u bend. Seems to me to be a straight forward job to replace the old valve with a hose tail and a bit of tubing exiting through the transom to give a maintenance free system.

The engine is a 1GM10 so does not have a huge amount of cooling water going through it and I do not want to divert too much from the exhaust injection point. Does anyone have a view on what size tubing I should us? I am thinking 6mm. It’s around two metres from the u-bend to the transom. Is there any danger that if the hose run is too long and the tube too narrow the vacuum will not be broken when the engine is turned off and cooling water stops being pumped?

Apart from making sure there are no kinks in the tubing, is there anything else to worry about when going to a valveless system?

 

[SHUG]

A 6mm tube sounds fine as the volume of water it would contain would not be sufficient to flood the exhaust piping.
You could however fit a new siphon valve which would give you a "dry" system where a ball valve blocks off the water outlet but lets air back in to vent the exhaust system.
ASAP do a nice one.http://www.asap-supplies.com/search/anti+siphon+valve/brass-siphon-break-valve-410023

 

[ricardio]

The ASAP valve looks interesting and rather more reasonably priced than a replacement Vetus fitting. Is there a quick way of checking that it is working and not seized up in the closed position?

 

[VicS]

I'd go along the suggestion of 6mm.

But why not look at the Vetus online catalog to see if they say what diameter tubing they supply

You will also see on the Vetus system that they fit a restrictor at the end of the hose. That will limit the amount of water diverted away from the exhaust.


Try to run the hose at the same level or a staedy gradient from one end to the other without lots of uphills and down hills and you should have no problems

The outlet can also be discharged into a cockpit drain where it is always visible. Probably also make you pee regularly until you get used to it though.

 

[Daydream believer]

perhaps you could make a very small hole in the top of the pipe just after it leaves the exhaust. It will drip a tiny bit but will help break the vacuum when you turn off the engine

 

[sailorman]

my syphon break is between the raw water pump & the engine h/e, it piddles into the cockpit drain so indicates if a blockage in the intake ( 3 times last year ) the pipe is about 8m/m with a hose clip that squeezes the pipe to restrict the flow

 

[prv]

The ASAP valve looks interesting and rather more reasonably priced than a replacement Vetus fitting. Is there a quick way of checking that it is working and not seized up in the closed position?

With the normal duck-bill valve, I have a short length of tubing attached which I occasionally blow into. This checks that air can still pass through it, and possibly blows away any crud that might be building up.

I'm not certain that the ASAP valve operates on the same principle, though.

Pete

 

[VicS]

I'd go along the suggestion of 6mm.



But why not look at the Vetus online catalog to see if they say what diameter tubing they supply

You will also see on the Vetus system that they fit a restrictor at the end of the hose. That will limit the amount of water diverted away from the exhaust.

Vetus dont in fact say the diameter but I estimate from the diagrams that it is about 9mm bore.

They supply 4m so 2m should be no problem

See the page from the catalog here

http://viewer.zmags.com/publication/04e44322#/04e44322/86

 

[ricardio]

Thanks to all for your helpful comments. 6mm hose with a clip to restrict flow if deemed necessary seems the way to go.

 

[PlankWalker]

I've got 3/8 on a 4 cylinder Perkins which works just right (stops piddling at tick-over)
I wouldn't go less than 6mm as it's easy to kink smaller sizes.