Anti siphon

[Skywalker]

I took her out for a spin last night to check on the newly installed water pump. Works like a charm. But wait, what is that? Water leaking? From where?

This time the water is running down the raw water hose. I trace it to the anti siphon fitting. Of course, I have to tear the interior half apart to get to this.

At the top of the fitting is the plastic valve. This fitting was new last year. There is some green corrosion at the base of the fitting, obviously it has weeped in the past. I notice that there is enough water around plug number four the boil up as the engine warms. And what is that? Rust beginning to form on my new plug. I mess around a little with the fitting.

I start the engine again, and...nothing. No leak. Run her for a while. No leak. The dreaded "intermittent" problem.

The valve on the fitting has a small hose barb. Obviously, this is part of the design. I'm guessing the solution is to put a length of hose on the fitting, rout it to the bilge, and move on.

Any other thoughts?

BTW, I have good flow out the tailpipe, she held a steady 160 under load.

Thanks.

Skywalker

[joe_db]

There is a tiny checkvalve in there that is easily clogged. In your case the clog is holding it open, but it can go the other way. I like adding a "pee hose" like an outboard has for this reason instead of using the anti-siphon valve, but your solution will work to keep water off the engine.

[Skywalker]

Thanks for the feedback Joe.

It turns out I'm having a hard time finding 1/8 inch hose.

Tomorrow, I'm going to try a pet/aquarium store.

Skywalker

[ndutton]

A caution

If attaching a hose to an antisiphon valve to manage the spitting or better yet doing away with the valve entirely and going to a vented loop also with water management hose, the hose must be resistant to kinking when hot. Note that clear vinyl hose will kink readily when heated with engine water.

When the hose kinks it seals itself off. An antisiphon needs to draw air in to work at all and a kinked spittle management hose defeats its function. I used braided fuel hose on my vented loop for just this reason.

[Skywalker]

Thanks, excellent point.

Chris

[sastanley]

skywalker...all good ideas above..this is a slippery slope, but a first world problem.

I have seen this anti-siphon valve with both hoses heading off to the bilge, and naked. My vented loop is naked up next to the galley sink, which as high as it can get it without it being in the middle of the boat. I can even hear it breathing at idle if I listen closely. I've never had enough spitting to cause me concern.

Perhaps a very short piece of hose to direct it away from the #4 plug??? Neil's right that any clear non-reinforced hose will buckle under any heat/pressure.

[Skywalker]

I'm headed to Boston for a fencing tournament, so I'll address this when I get home.

The raw water of my FWC doesn't seem to be much more than warm, so I am surprised by your warnings about using clear hose.

My fitting is dead center of the boat, right up to the bridge deck. Perfect location, which is why plug number four is directly under it!

Given it's location, I should have some options for redirecting, either into the bilge or just aft toward the cutlass/shaft.

Skywalker

[ndutton]

The raw water of my FWC doesn't seem to be much more than warm, so I am surprised by your warnings about using clear hose.

My fitting is dead center of the boat, right up to the bridge deck. Perfect location, which is why plug number four is directly under it!

Don't discount the added effect of ambient heat in the area. It's right above #4, the exhaust is therefore directly beneath the A/S and its heat radiates upward into a pocket formed by the bridge deck. Clear vinyl hose gets soft if left in the sunlight so it doesn't take much. Consider too that the A/S orientation is directly upward so the hose must make an abrupt U-turn right there.

Although not part of Sky's original post I'd like to take the opportunity to make a case for scrapping the A/S valve in favor of a vented loop. The advantage of a simple loop is no mechanism to fail.

[Whippet]

pic?

Hi Neil:

Do you have a photo or sketch of a recommended loop? I'm ok ditching my MMI A/S valve, but want to be clear what I'm replacing with. My water exhaust loop above WL is currently constructed with the 1/2" red MMI heater hose.

thanks much

[ndutton]

Here's a drawing and pdf (for zooming and/or printing) of my FWC system. The anti siphon loop and spittle hose are shown.

All you need to do is remove the A/S valve, thread a small hose barb in its place and direct an attached hose (I use 1/4") to where you want the water to go. Mine goes overboard via the galley sink drain. It's the top loop of the spittle hose that's prone to kinking so plan for it.

[Whippet]

thanks

Thanks for sketch, Neil. I dont have access to sink drain but will look to improvise elsewhere.