Engine Anti-Siphon Valve - Temporary Replacement

[Bay Pelican]

While doing some maintenance work on my wing engine I started it to find that the 16 year old anti-siphon valve had failed. With the engine running salt water was spurting out of the valve showering the engine.

The fix of course was to replace the valve. In luck I was able to find one and swap it out. All is well for now.

While waiting to get to the chandlery and not knowing if an anti-siphon valve could be had on this island I considered alternatives. What I came up with as an alternative was a manual valve that could be closed when the engine was started and opened for a couple of seconds when the engine stopped to break the suction. Basically a brass T in the hose line with a ball valve on the third opening of the T.

Thoughts. Would this have worked barring operator error in forgetting to manually open and close the valve?

 

[Wxx3]

Don't see why not.
Good idea to keep in the back of my mind.

 

[O C Diver]

Why do you need a valve? Was considering adding an anti-siphon valve to my engine when I repowered. Then thought if I did, I would route a piece of 3/8" hose from the top of the loop to the galley sink drain pipe after the P trap which is 4' above my engine. Have seen numerous pics of engine rooms where there is or was some spray from the valve that has corroded stuff. Thought routing the vent to an overboard discharge was a cleaner solution. Any reason that wouldn't work?

Ted

 

[HiDHo]

I would think that the 3/8" hose would work but not sure about the height above the loop. It might have to be higher than the pump specs for lift. It would be worth trying as we have had the same problem on our generator anti-siphon valve not opening when we shut down. The fix was to lengthen the hose back to the pump which creates enough water weight in it to open the siphon valve. That fixed our problem.

 

[LarryM]

Why do you need a valve? Was considering adding an anti-siphon valve to my engine when I repowered. Then thought if I did, I would route a piece of 3/8" hose from the top of the loop to the galley sink drain pipe after the P trap which is 4' above my engine. Have seen numerous pics of engine rooms where there is or was some spray from the valve that has corroded stuff. Thought routing the vent to an overboard discharge was a cleaner solution. Any reason that wouldn't work?

Ted

Ted,

I recently reworked some of my exhaust plumbing and installed a Groco vented loop vacuum break which had been omitted from a prior re-power. I chose the pricey Groco unit because if its large vacuum breaker diaphragm and reputation for being reliable. After I finished the installation, I ran across this article on Designing a Marine Exhaust System by Tony Athens at Seaboard Marine. Sections 5 and 8 discuss the subject of anti-syphon bypass.

While everything was still accessible, I installed an active bypass in the uphill cooling water discharge line before it enters the vented loop and goes over the top into the muffler. This bypass discharges overboard via a through-hull above the waterline. It provides a redundant, positive vacuum break upon engine shut-down, and a visual indication of cooling water flow when the engine is running. Actually, it is similar in concept to the water that flows from the cooling water tell-tale (pee hole) on an outboard motor.

Being cautious, I also installed an in-line ball valve so I could control the bypass flow or close it completely in the event of a weak or failing raw water pump. Tony also mentioned that the raw cooling water flow was greater than what was actually needed to cool the exhaust system, and that reducing the flow also reduces exhaust back pressure. I found this to be true as I am bypassing about 1/3 of the cooling water and the muffler still runs under 100F at every engine speed and load. One additional safety feature is that the risk of filling a water-lift muffler due to prolonged cranking is reduced or even eliminated.

Finally, this arrangement seems to be common on commercial vessels with wet exhaust for safety, and some sportfishing boats for performance.

YMMV

 

[Ski in NC]

Fairly common to replace the anti siphon valve with a tee fitting and a little vent line. Run the vent line to a sink drain, deck drain or even a little dedicated through hull fitting. Better actually, as there are no moving parts to stick. Best to route somewhere that the dribble is visible. Hose must be routed so it does not form loop traps.