Anti-Siphon Loop for Raw Water Exhaust

[Wotname]

Originally Posted by Guy

Go even further and plumb that little line from the top of the loop somewhere. Some take it into the cockpit. I have 1/4" hose going to a small through hull high up on the side of the boat that I can touch sitting in the cockpit. As bonus not to be scoffed at, you can feel the water temp of your engine with your fingers. You can also tell more about the water flow from the pump by how much water coming out of the hose . It's not really that much water on our boat with a Perkins, more like a big dribble of warm water.

Yes, this is actually on my "to do" list. Just waiting for some more gas before welding up a nice custom fitting to take the tell tale water into the cockpit - directly above one of the drains!

Nothing quite like seeing the tell tale water going out to know all is good

[Wotname]

Originally Posted by Hudson Force

Good news for me! In the two hours since Wotname's post recommending the tube extension I've eaten supper, cleared things away, washed the dishes and added a 2.5 foot tube to my failed anti-siphon vent that leads to the top of my starboard cockpit locker. At this point I can observe that the head pressure will prevent the water from rising to this level or easily cap the tube without crawling into the far reach of my engine room after running.

Regardless of my final solution (and thanks for all the other ideas) I'm good for the next two weeks until I get a new part or decide to keep the extension tube.

KISS is good!

[S/V Alchemy]

Originally Posted by Hudson Force

Thanks Rick, I would rather have this than the galvanized pipe fitting too. This is likely my best choice.

Having had this particular issue bite me in the past, you may wish to consider the most simple option: a simple barb or nipple at the top of the loop, to which is double-clamped a length of hose going all the way to the deck or cockpit level. The requirement is "must be open to the atmosphere"; the occasional squirt of warm water onto the deck or one's toes demostrates this.

It's the little piston that can screw up. Loops and flappers and a properly sized waterlift can keep the sea from pushing back into the engine, or even (and here I'm going to sound radical) a seacock at the exhaust end if you are making a passage. I have good, quick access to all my through hulls/seacocks. When I'm doing a lot of sailing, I close them all unless I need to run water. But perhaps that's a bigger question than you are asking.

[S/V Alchemy]

Originally Posted by Wotname

Why have a valve at all. Just take a small diameter tube from the high point of the loop and run it vertical for a couple of feet.

There is no real pressure in the raw water loop, the water will be pushed many a foot into the tube when running but will provide the siphon break when at rest.

There is the exhaust pressure to contend with but I have found that the tube can usually be taken high enough to cope.

Of course, YMMV.

I should have read the entire thread!

[exMaggieDrum]

Originally Posted by Wotname

Why have a valve at all. Just take a small diameter tube from the high point of the loop and run it vertical for a couple of feet.

There is no real pressure in the raw water loop, the water will be pushed many a foot into the tube when running but will provide the siphon break when at rest.

There is the exhaust pressure to contend with but I have found that the tube can usually be taken high enough to cope.

Of course, YMMV.

I did it this way and it works like a champ. No moving parts!

[GrahamHO]

Similar to Rick and other's photos I have a plastic Vetus anti siphon loop. They have a model with a bleed hole and no valve to stick. Run a small diameter flexible hose from the small pipe on the Vetus and out the transom. A small dribble of water runs out when the motor is running. The Vetus kit includes the small diameter flexible hose and matching skin fitting for the transom. Mount the Vetus centrally. In my case at a high point under the cockpit floor. Run the small hose with a number of clips to prevent sagging.
The cooling water runs from the engine around the loop and back to the exhaust bend. A small quantity of water bleeds out into the small hose and air comes back in when the engine is stopped.


Avoid the type with a valve as the valve can stick with salt etc.

[Nicholson58]

Originally Posted by Wotname

Why have a valve at all. Just take a small diameter tube from the high point of the loop and run it vertical for a couple of feet.

There is no real pressure in the raw water loop, the water will be pushed many a foot into the tube when running but will provide the siphon break when at rest.

There is the exhaust pressure to contend with but I have found that the tube can usually be taken high enough to cope.

Of course, YMMV.

The probability of this working is not assured. This will depend on your motor, plumbing and raw water flow among other things. You could experiment to see how high you need to go but the down side is that you could damage the engine or flood the bilge. Possibly also over heat the exhaust line.

Here is our GROCO with a vice grip. The diaphragm failed to re-seat. The Bilge was filling with a lot of water over a long running time. Solution is new seal & re-pipe to a through port instead of the bilge.

BTW, if you do not remove the temporary pinch, you risk hydro-locking the pistons - big damage.

[sartorst]

Originally Posted by exMaggieDrum

I did it this way and it works like a champ. No moving parts!

I'm thinking of doing this but, would have a sag in vent line in which water could collect. If I run it the easy way, what are your thoughts? Or is it a must to be a continuous climb to the overboard point? Thanks for any advice!

[sartorst]

Originally Posted by Wotname

Why have a valve at all. Just take a small diameter tube from the high point of the loop and run it vertical for a couple of feet.

There is no real pressure in the raw water loop, the water will be pushed many a foot into the tube when running but will provide the siphon break when at rest.

There is the exhaust pressure to contend with but I have found that the tube can usually be taken high enough to cope.

Of course, YMMV.

I'm thinking of doing this but, would have a sag in vent line in which water could collect. If I run it the easy way, what are your thoughts? Or is it a must to be a continuous climb to the overboard point? Thanks for any advice!

[GrahamHO]

Originally Posted by sartorst

I'm thinking of doing this but, would have a sag in vent line in which water could collect. If I run it the easy way, what are your thoughts? Or is it a must to be a continuous climb to the overboard point? Thanks for any advice!

I ran my vent line from the Vetus along the central underside of the cockpit floor and clipped it about every 30 cm or 1' to eliminate sagging. Under the tiller there is a locker set into the cockpit floor, so I connected the vent hose to a Y piece and ran small vent hoses on each side of the locker to 2 very small plastic skin fittings in the transom like twin exhausts. That was so the the vent hose would drain whichever side the boat may be heeled when stopping the motor and sailing.

A siphon without a vent can operate over quite a height. During a drought a farmer friend borrowed a tanker truck from a milk factory where he filled it with water. He drove to his farm and pumped the water into his large water tank through a hose. Then he dropped the hose on the ground and drove back for another load of water. When he arrived back with the second load, he found that the tank was almost empty again as most of the water had siphoned out of the tank through the hose he had dropped on the ground.

The same can happen in your motor (without a bleed vent) with water siphoned in through the water pump and filling the exhaust without the exhaust pressure to force it out the back. Then when you start your motor one cylinder with an open exhaust valve can be full of water. The other cylinder/s fire and the cylinder full of water bends a conrod. I know this for an expensive fact, which is why after overhauling my engine I installed a Vetus exhaust vent. Expensive, though cheap insurance.

The radial engines on piston planes have at least one cylinder at the bottom. Before starting them after they have been standing, they are turned over by one one or 2 people manhandling the propellor so many turns. This is in case oil has drained into a lower cylinder, which could hydraulic and crack the cylinder or blow it off.

[Wotname]

Originally Posted by GrahamHO

…….

A siphon without a vent can operate over quite a height. …....

IIRC from high school physics, that height is about 32 ft
but I might not recalling correctly .

Anyone know for sure????

[Wotname]

Originally Posted by Nicholson58

The probability of this working is not assured. This will depend on your motor, plumbing and raw water flow among other things. You could experiment to see how high you need to go but the down side is that you could damage the engine or flood the bilge. Possibly also over heat the exhaust line.
………..

This is true and yes, I concur that experimenting is necessary to be sure.

However, it is unlikely to damage the engine, flood the bilge or overheat the exhaust if one is judicious when trying it out .

Start with small clear tube (1/4") and run it vertically from the top of the anti siphon loop leaving the top end open to the atmosphere. For most (but not all) installations, the resultant water level in the small tube will only be 1 or 2 feet. If so, make the tube say another foot or so longer and all should be sweet. Check while under way at extreme angles of heal.

Given the above tube and height, the most water that can run back anywhere will be around 15 to 20 ml; that is 3 to 4 teaspoons. This should be accommodated by the mixing elbow & exhaust system.

But yes, do check that it work with your installation before committing to this full time

[GordMay]

Originally Posted by Wotname

IIRC from high school physics, that height is about 32 ft ...

✓ You recall correctly.

Pressure can be converted to head by the following formula:
Head = (Pressure x 2.31*) ÷ Specific Gravity

* 2.31 feet of fresh water equals 1 psi.

If atmospheric pressure is 14.7 psi at sea level, and we are talking about fresh water (sg.1); 14.7-psi. would convert to 33.96* feet of head:
Head = (14.7 x 2.31) ÷ 1 = 33.96 Feet*

* In actual practice, friction in the hose will reduce that theoretical head to something around 32'.

Seawater (@36 Deg) has an SG of 1.02, thus:
Head = (14.7 x 2.31) ÷ 1.02 = 33.39 Ft. (less friction loss).

[roland stockham]

The valve is unnecessary, just lead a 1/4" pipe overboard from the top of the loop so that it drains well above the waterline. If it bleeds a small amount of water when the engine is running will stop it clogging. Anti-siphon valves running hot water always have problems with salt clogging.

[GrahamHO]

Originally Posted by Wotname

IIRC from high school physics, that height is about 32 ft
but I might not recalling correctly .

Anyone know for sure????

Yes I was also recalling 32'. That's when the weight of water matches the atmospheric pressure. I think......It would depend exactly on your altitude but most boats sail at sea level.