proper functioning vented loop

Aug 14, 2011
182
Hunter 35.5 Legend PCYC Shediac, NB
I have a Jabsco Electric head that did not draw much sea water in during flushing. So my first fix was to install a complete maintenance kit since i did not know how old they were. Great experience to learn how a system works is tear it down to every part and reassemble. Things work great but still not drawing much water. My next try was to put my finger over the vented loop and flush. Works great draws a good supply of water.
How does a vented loop actually work ? is this functioning correctly or do i need to adjust it?


Thanks for your help
 
Dec 14, 2003
1,393
Hunter 34 Lake of Two Mountains, QC, Can
A vented loop has a dua function: to let air in when you're drawing from the tank (i.e. your water or fuel tanks) and to let air out when you're putting stuff in the tank (fuel, water or waste). If it gets blocked then it creates a problem when you try to put stuff in and also when you're trying to get stuff out. For exemple if it's blocked, your engine fuel pump may have problems get enough fuel to the engine at higher rpm or your freshwater pump may not deliver the proper amount of water to the faucets. In the case of your Electric Head, if the vented loop is blocked then the pump may have problems pushing the waste in the tank and hence might have problems pulling water. Get a bucket, disconnect the head water supply at the head and pump. That will show whether you get a good supply of seawater or not. If you do than your problem is not with the pump itself. A simple way to check the vent is first to get a thorough pump-out to clean the tank, then fill it completely with water until water come out the vent in a good volume. If no water or just a little comes out, then your vented loop hose is blocked. Generally at the through-hull by insects but it might also be at the connector to the tank by solid waste. You need to ensure that air is totally free to go in and out of the tank for the system to work properly. Good luck.
 

jviss

.
Feb 5, 2004
6,745
Tartan 3800 20 Westport, MA
Did this ever work correctly, i.e., did it ever draw sufficient water? What you describe sounds to me like the vented loop may be on the wrong side of the pump. It shouldn't be between the seacock and the pump, it should be after the pump, i.e., on the pressure, not suction side of the pump.
 

jviss

.
Feb 5, 2004
6,745
Tartan 3800 20 Westport, MA
A vented loop has a dua function: to let air in when you're drawing from the tank (i.e. your water or fuel tanks) and to let air out when you're putting stuff in the tank (fuel, water or waste). If it gets blocked then it creates a problem when you try to put stuff in and also when you're trying to get stuff out. For exemple if it's blocked, your engine fuel pump may have problems get enough fuel to the engine at higher rpm or your freshwater pump may not deliver the proper amount of water to the faucets. In the case of your Electric Head, if the vented loop is blocked then the pump may have problems pushing the waste in the tank and hence might have problems pulling water. Get a bucket, disconnect the head water supply at the head and pump. That will show whether you get a good supply of seawater or not. If you do than your problem is not with the pump itself. A simple way to check the vent is first to get a thorough pump-out to clean the tank, then fill it completely with water until water come out the vent in a good volume. If no water or just a little comes out, then your vented loop hose is blocked. Generally at the through-hull by insects but it might also be at the connector to the tank by solid waste. You need to ensure that air is totally free to go in and out of the tank for the system to work properly. Good luck.
I am afraid that you are conflating a tank vent with a vented loop. What you explain as the function of a vented loop is incorrect. What you describe is the function of a simple tank vent. A vented loop is different.

A vented loop is a loop in a plumbing line with an anti-siphon valve. It allows the system to push fluids through the loop, but if the pressure drops a one-way "vent" valve opens, the anti-siphon valve, to prevent siphoning of fluids. The "vent" refers to the anti-siphon valve, not a simple tank vent.

Here's a pic:



Here's the article from which the pic comes:

Anti-Siphon Valve Basics - BoatUS Magazine
 
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Aug 14, 2011
182
Hunter 35.5 Legend PCYC Shediac, NB
jviss said:
Did this ever work correctly, i.e., did it ever draw sufficient water? What you describe sounds to me like the vented loop may be on the wrong side of the pump. It shouldn't be between the seacock and the pump, it should be after the pump, i.e., on the pressure, not suction side of the pump.

It did work correctly last fall but we did notice
Did this ever work correctly, i.e., did it ever draw sufficient water? What you describe sounds to me like the vented loop may be on the wrong side of the pump. It shouldn't be between the seacock and the pump, it should be after the pump, i.e., on the pressure, not suction side of the pump.

It did work fine last summer but in the fall the water was becoming less. The vented loop is on the sea water supply line between the seacock and the electric toilet which socks water when pushing the flush button. My holding tank is empty as we have been using it the last few weeks and just pumped out prior to installing the maintenance kit.
 

jviss

.
Feb 5, 2004
6,745
Tartan 3800 20 Westport, MA
I am not a plumbing professional or expert, but I'm pretty sure the vented loop should not be between the seacock and the toilet. When the toilet attempts to pump by applying suction to that line, the suction will tend to open the vent valve. The fact that it moves any water is interesting. The vented loop should be in the line from the pump to the bowl. Check this diagram from the Jabsco manual:


First, make sure of what you have. Draw a diagram. Then, if it's incorrect, correct it!
 
Aug 14, 2011
182
Hunter 35.5 Legend PCYC Shediac, NB
I am not a plumbing professional or expert, but I'm pretty sure the vented loop should not be between the seacock and the toilet. When the toilet attempts to pump by applying suction to that line, the suction will tend to open the vent valve. The fact that it moves any water is interesting. The vented loop should be in the line from the pump to the bowl. Check this diagram from the Jabsco manual:


First, make sure of what you have. Draw a diagram. Then, if it's incorrect, correct it!
I understand but I have an electric head so it only draws water when I push the button. Should I remove the vented loop ?
 
Aug 14, 2011
182
Hunter 35.5 Legend PCYC Shediac, NB
Although that's a drawing in the Jabsco manual, every manual toilet instructions show the vented loops in same locations.

--Peggie
Thanks Peggy, But should I remove the vented loop al together ? My discharge line goes straight to my holding tank, I do not have a through hull discharge. Then my holding tank is vented through a mushroom style screened vent and systems seems to work well. I have been adding fresh water by hand to the bowl to ensure line gets emptied
 
Dec 2, 1997
8,709
- - LIttle Rock
Vented loops are siphon breakers...they have nothing in common with tanks vents. You're also confusing discharge vented loops with flush water intake vented loops.. and yes, sea water electric toilets do need an intake vented loop unless your toilet is above waterline, which is unlikely on your boat.

Where to put it depends on the make/model of your toilet...if it's a 37010, it belongs in the line that connects the pump to the back of the bowl, same as it should be on a manual toilet. If it's one of the all china thrones that doesn't have line connecting the pump to the bowl, It has to go in the line between the thru-hull and the pump, but with a solenoid valve wired to the flush button---one of the two types shown in the attached photos---that opens and closes the air valve.

--Peggie

Jabsco 37068-2000 vented loop with solenoid valve.jpgjabsco 37038-12 solenoid valve.jpg
 
Dec 14, 2003
1,393
Hunter 34 Lake of Two Mountains, QC, Can
Hi JVISS, Thanks for picking up on my snafu ! I simply read the op diagonally and reacted immediately. You are right of course that a vented-loop is different than a tank vent. And yes I am aware of the difference ! And also well aware on how they work and what they do ! It was my mistake and I'm glad someone picked-up on it so that hopefully it did not create a problem.

I am afraid that you are conflating a tank vent with a vented loop. What you explain as the function of a vented loop is incorrect. What you describe is the function of a simple tank vent. A vented loop is different.

A vented loop is a loop in a plumbing line with an anti-siphon valve. It allows the system to push fluids through the loop, but if the pressure drops a one-way "vent" valve opens, the anti-siphon valve, to prevent siphoning of fluids. The "vent" refers to the anti-siphon valve, not a simple tank vent.

Here's a pic:



Here's the article from which the pic comes:

Anti-Siphon Valve Basics - BoatUS Magazine
 
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Likes: jviss
Dec 2, 1997
8,709
- - LIttle Rock
I think she was asking if it's necessary to have a vented loop in a toilet discharge line if the toilet ONLY flushes into the toilet...the answer to that is no.

However, a vented loop IS needed in the flush water intake line...to prevent sea water from flooding--and even overflowing--the bowl if the toilet is left in the "wet" mode when the intake thru-hull is open.

--Peggie
 

jviss

.
Feb 5, 2004
6,745
Tartan 3800 20 Westport, MA
Come to think of it, mine doesn't have a vented loop between the flush water pump and the bowl, as I think it should, but I believe the top edge of the bowl is above the water line. Would that be O.K.?
 
Dec 25, 2000
5,704
Hunter Passage 42 Shelter Bay, WA
Our 1991 boat came standard with dual electric Jabsco toilets both having siphon breaks between the intake through hull and the pump. It would appear in our layout that the siphon break might not be closing completely during the flushing mode thus allowing air into the system preventing sufficient water to reach the bowl. The other possibility is a critter becoming stuck in the through hull preventing sufficient water into the system. That did happen to us several years ago and the solution was to connect city water to the intake hose to clear the through hull.