Vented Loop Vacuum Breaker

[Manateeman]

Has anyone found a better vacuum breaker than the little duck bill valve at the top of the Forespar vented loop?
We clean them but they are so small and we don’t feel comfortable with the design. Seems like a small amount of “stuff” could prevent them from opening.
Forespar has a video but it’s difficult to determine if the duckbill needs to be replaced as they are rather vague about when to do this...medical grade duckbill valves seem to last forever. We are trying to find a source to replace the Forespar duckbill with something more foolproof.
Anything better which could be added to these vented loops?
Thank you for replies.
The manatee crew

[Uncle Bob]

Originally Posted by Manateeman

Has anyone found a better vacuum breaker than the little duck bill valve at the top of the Forespar vented loop?
We clean them but they are so small and we don’t feel comfortable with the design. Seems like a small amount of “stuff” could prevent them from opening.
Forespar has a video but it’s difficult to determine if the duckbill needs to be replaced as they are rather vague about when to do this...medical grade duckbill valves seem to last forever. We are trying to find a source to replace the Forespar duckbill with something more foolproof.
Anything better which could be added to these vented loops?
Thank you for replies.
The manatee crew

I guess the question is just where is this vented loop installed, if it is in the exhaust water discharge then replacing the valve with a small diameter tube discharging overboard is the go, if it is in the grey or black water discharge then perhaps not.

[noelex 77]

Originally Posted by Uncle Bob

I guess the question is just where is this vented loop installed, if it is in the exhaust water discharge then replacing the valve with a small diameter tube discharging overboard is the go, if it is in the grey or black water discharge then perhaps not.

Agreed. Valve based vented loops do have a habit of failing. I recently purchased a new valve based vented loop that was stuck out of the box.

There is a limited number of ventilated loops that are critical. For many sailing boats this is only the main engine.

If the vented loop to the main engine fails the engine can suffer catastrophic damage. A simple overboad "pissing tube" rather than a rubber valve is more sensible for this application. Unfortunately this rarely fitted on modern boats. A vented loop without a rubber valve ( a basic overboard "pissing tube") is very unlikely to fail. It has no moving parts to jam. It can be checked every time the engine is started although it should never fail or need any service.

There are many other vented loops on a sailboat. Most of these are much less critical. A stuck valve in the vented loop is likely to cause only a minor problem. For these application a rubber "duck billed valve" together with some routine maintenance and an occasional check that the the valve is OK is fine. Consider shutting off the seacock to these systems when leaving the boat.

[Benz]

How does the pissing tube create the needed vacuum to begin with? I've had very bad luck with vented loops, and now I flush the toilet by putting a finger over the vacuum break in the inlet hose. Luckily the exit hose duckbill still works.....

[noelex 77]

Originally Posted by Benz

How does the pissing tube create the needed vacuum to begin with?

It lets air in to prevent a syphon. There is no rubber valve and therefore no mechanical device to wear out, stick, or to go wrong.

The syphon break in this case is a simple vent tube.

[peghall]

I've had very bad luck with vented loops, and now I flush the toilet by putting a finger over the vacuum break in the inlet hose. Luckily the exit hose duckbill still works.....

That's because it's installed in the wrong place. The intake vented loop shouldn't be in the line from the thru-hull to the pump...it belongs in the line between the bowl and the pump. See where it has to go in the drawing on p.3 of the Jabsco manual toilet owners manual Jabsco Manual Twist & Lock owners manual ...Figure 2 on p. 5 in the Raritan PHII owners manual PH II Owner’s Manual ...and Figure 5 on page 5 of the Raritan PH SuperFlush (newest version of the PHII) Raritan SuperFlush Owners Manual As you'll see, it's in the same place in all of 'em: between the pump and the bowl (if installed between the thru-hull and the pump it interferes with the pump's ability to prime). It needs to be at least 6-8" above waterline AT MAX HEEL, not just when the boat's at rest..which puts it about 2-3' above the bowl on most sailboats. That requires replacing the short piece of hose mfrs use to connect the pump to the bowl with two lengths of 3/4" sanitation hose long enough to put the loop where it needs to be. There are a few toilets that make this impossible--bronze "thrones" like the W-C Skipper, Groco Model K are two and maybe the Lavac, but you'll find the same instructions in the owners manuals for every "normal" manual toilet.

And btw... a vent line instead of an air valve on a vented is a bad idea because that hose has to be so small that it quickly becomes blocked by salt and sea water minerals...turning a vented loop into an UNvented loop that no longer has any ability to prevent a siphon. Because it also quickly becomes "out of sight, out of mind," no one ever thinks to clean it out.


--Peggie

[CarinaPDX]

Look at the Groco anti-siphon loops: https://www.groco.net/products/marin...n/vented-loops . They are very resistant to clogging. The tiny valves used in most anti-siphon loops are just too small and fiddly. It is possible to add a small line on top of the valve to drain any water that escapes the valve. Note that the drain line needs to terminate well above any source of water.

Greg

[Uncle Bob]

Originally Posted by peghall

I've had very bad luck with vented loops, and now I flush the toilet by putting a finger over the vacuum break in the inlet hose. Luckily the exit hose duckbill still works.....

That's because it's installed in the wrong place. The intake vented loop shouldn't be in the line from the thru-hull to the pump...it belongs in the line between the bowl and the pump. See where it has to go in the drawing on p.3 of the Jabsco manual toilet owners manual Jabsco Manual Twist & Lock owners manual ...Figure 2 on p. 5 in the Raritan PHII owners manual PH II Owner’s Manual ...and Figure 5 on page 5 of the Raritan PH SuperFlush (newest version of the PHII) Raritan SuperFlush Owners Manual As you'll see, it's in the same place in all of 'em: between the pump and the bowl (if installed between the thru-hull and the pump it interferes with the pump's ability to prime). It needs to be at least 6-8" above waterline AT MAX HEEL, not just when the boat's at rest..which puts it about 2-3' above the bowl on most sailboats. That requires replacing the short piece of hose mfrs use to connect the pump to the bowl with two lengths of 3/4" sanitation hose long enough to put the loop where it needs to be. There are a few toilets that make this impossible--bronze "thrones" like the W-C Skipper, Groco Model K are two and maybe the Lavac, but you'll find the same instructions in the owners manuals for every "normal" manual toilet.

And btw... a vent line instead of an air valve on a vented is a bad idea because that hose has to be so small that it quickly becomes blocked by salt and sea water minerals...turning a vented loop into an UNvented loop that no longer has any ability to prevent a siphon. Because it also quickly becomes "out of sight, out of mind," no one ever thinks to clean it out.


--Peggie

Peggie, I have to differ with you here, my boat is fitted with a 1/4 inch hose line from the top of the elbow to a nearby cockpit drain, was there when purchased around 10 years ago and obviously not new then and has continued to perform ever since. It gets a look at every time I change the oils, so annually and no clogging to date.

[peghall]

There are always "exceptions that prove the rule." Glad yours is one of 'em.


--Peggie

[noelex 77]

Yes, a vent line is much less likely to clog than a valve, in my view.

It is also easy to check just by making sure water is exiting.

With a valve operated vent, unless you can see the water level the valve has to be removed. Even then, to be sure of correct operation with most models the whole vented loop needs to be removed so you can check with air pressure.

[MJH]

Originally Posted by Manateeman

Has anyone found a better vacuum breaker than the little duck bill valve at the top of the Forespar vented loop?
We clean them but they are so small and we don’t feel comfortable with the design. Seems like a small amount of “stuff” could prevent them from opening.
Forespar has a video but it’s difficult to determine if the duckbill needs to be replaced as they are rather vague about when to do this...medical grade duckbill valves seem to last forever. We are trying to find a source to replace the Forespar duckbill with something more foolproof.
Anything better which could be added to these vented loops?
Thank you for replies.
The manatee crew

I inherited a vented loop on one of my bilge pumps that is located rather high and without a duck bill valve...it is open, and a long stiff tube upwards from there. There is nothing to clog.

~ ~ _/) ~ ~ MJH

[CarinaPDX]

With my old engine's cooling system I replaced the unreliable valve on top of the loop with a hose barb and ran a 1/4" hose out to the footwell. It never plugged up. The trickle was proof that the water pump was moving water. Good solution.

Greg

[peghall]

How much air pressure should there be in a toilet intake line/vented loop?


--Peggie

[noelex 77]

Originally Posted by peghall

How much air pressure should there be in a toilet intake line/vented loop?


--Peggie

Peg, I was trying to be polite . It seems there is no way to discuss testing valve operated vented loops without mentioning the "suck and blow" technique .

Of course this test is not recommended for vented loops in the toilet system . I guess you could use a dingy pump.

To Test Loop for Pressure:
Plug one end of the loop and blow into the loop. No air should escape.
To Test Loop for Vacuum:
Plug one end of the loop and suck on the other end. Air should enter under this slight negative pressure.

[Benz]

Originally Posted by peghall

I've had very bad luck with vented loops, and now I flush the toilet by putting a finger over the vacuum break in the inlet hose. Luckily the exit hose duckbill still works.....

That's because it's installed in the wrong place. The intake vented loop shouldn't be in the line from the thru-hull to the pump...it belongs in the line between the bowl and the pump. See where it has to go in the drawing on p.3 of the Jabsco manual toilet owners manual Jabsco Manual Twist & Lock owners manual ...Figure 2 on p. 5 in the Raritan PHII owners manual PH II Owner’s Manual ...and Figure 5 on page 5 of the Raritan PH SuperFlush (newest version of the PHII) Raritan SuperFlush Owners Manual As you'll see, it's in the same place in all of 'em: between the pump and the bowl (if installed between the thru-hull and the pump it interferes with the pump's ability to prime). It needs to be at least 6-8" above waterline AT MAX HEEL, not just when the boat's at rest..which puts it about 2-3' above the bowl on most sailboats. That requires replacing the short piece of hose mfrs use to connect the pump to the bowl with two lengths of 3/4" sanitation hose long enough to put the loop where it needs to be. There are a few toilets that make this impossible--bronze "thrones" like the W-C Skipper, Groco Model K are two and maybe the Lavac, but you'll find the same instructions in the owners manuals for every "normal" manual toilet.

And btw... a vent line instead of an air valve on a vented is a bad idea because that hose has to be so small that it quickly becomes blocked by salt and sea water minerals...turning a vented loop into an UNvented loop that no longer has any ability to prevent a siphon. Because it also quickly becomes "out of sight, out of mind," no one ever thinks to clean it out.


--Peggie

Thank you for this. I'm afraid that with my Lavac it's impossible to rig as you describe, since the whole circus depends on suction, and I'd never get a prime with an open tube.
But you've confirmed that until a reliable duckbill valve is made, the finger method will prevail.