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Old 12-06-2016, 20:49   #1
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When are vented loops required?

I'm going to be putting in an order for some parts for my head installation and I'm wondering when are vented loops really necessary?

My install will be like this:

- Jabsco manual head will be installed below the waterline.
- A dedicated 3/4" intake with seacock will be used for the "fresh" water.
- The head discharge will go through a 1-1/2" pipe direct to a holding tank.
- The holding tank discharge will be through a 1-1/2" pipe.
- The discharge pipe will be connected with a Y-valve, one way leading to a deck pump out and one way leading to the dedicated 1-1/2" discharge seacock.
- A manual discharge pump will be connected in series with the Y-vale and seacock.

Do I require any vented loops for this system? Perhaps on the intake line, but on the discharge the seacock will be closed and will have the Y valve shut off as well.

Appreciate any advise.
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Old 12-06-2016, 21:05   #2
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Re: When are vented loops required?

Will you always remember to shut off the ovb port?
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Old 12-06-2016, 21:20   #3
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Re: When are vented loops required?

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Originally Posted by ElCapt Drew View Post

Do I require any vented loops for this system? Perhaps on the intake line, but on the discharge the seacock will be closed and will have the Y valve shut off as well.

Appreciate any advise.
NOT ever on the intake line.

Always on the line between the pump on the head and the bowl.

Suggest you read the installation manual you get with your head or download one now and read it.
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Old 12-06-2016, 21:28   #4
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Re: When are vented loops required?

As Stu said, you'll need only one...in the head intake. However, it has to be between the pump and the bowl--which requires replacing the short piece of hose the mfr used to connect them--and needs to be at least 6-8" above the boats waterline at ANY angle of heel..which on most sailboats puts it 2-3' above the bowl. See the drawing for below waterline installation in the installation instructions for your toilet.

If you mount the tank overboard discharge pump above the tank, you can get away without a vented loop in that line (it would go between the pump and thru-hull). However, whether there's loop in that line or not, that thru-hull should always be closed except while dumping the tank. If you leave it open, pressure of the water against the hull while underway can fill up the tank with sea water. A macerator pump mounted low will only slow it down, it won't block it.
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Old 12-06-2016, 22:18   #5
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Re: When are vented loops required?

The reason you don't put a vented loop between the seacock and the toilet is that it lets air into the line and reduces the suction that the pump can create. Replace the hose that goes from the pump to the back of the bowl with a longer hose you can run up above the water line. Put the vented loop in this hose. Jabsco has a drawing of this in the instructions that come with the toilet.
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Old 12-06-2016, 22:47   #6
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Re: When are vented loops required?

With most installations I've been around, or worked on, people tend to go to some efforts in order to get the top of the bowl above the WL, when the boat's at rest. Designer's included.
As in some instances, it's another thing which will help to reduce the odds of flooding. If someone forgets to close the valves, when leaving the boat.
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Old 13-06-2016, 07:18   #7
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Re: When are vented loops required?

And the reason you do not need a vented loop on the outlet line is that, from what you've said, there will be no way to connect it directly to a seacock. All connections will go through the holding tank first. The holding tank, because it is vented itself, functions like a big vented loop on that side of the plumbing.

The basic rule is that you want a vented loop in any line where it might be possible to create a siphon between a seacock and the interior of the boat. In your case, that would only be possible on the intake side.

Good luck!
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Old 13-06-2016, 09:55   #8
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Re: When are vented loops required?

Quote:
Originally Posted by ElCapt Drew View Post
...The discharge pipe will be connected with a Y-valve, one way leading to a deck pump out and one way leading to the dedicated 1-1/2" discharge seacock...
Substitute a sanitary Tee for the Y-valve.
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Old 13-06-2016, 10:00   #9
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Re: When are vented loops required?

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Substitute a sanitary Tee for the Y-valve.
Yes, you don't need a troublesome Y valve. If the Seacock is open you are overboard, if not , it goes the other way.
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Old 13-06-2016, 10:12   #10
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Re: When are vented loops required?

There are configurations that allow odors to backup from holding tanks to toilet - not a broad idea to add a vented loop in the outlet.


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Old 13-06-2016, 10:17   #11
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Re: When are vented loops required?

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Yes, you don't need a troublesome Y valve. If the Seacock is open you are overboard, if not , it goes the other way.
Y valves are accepted by the environmental folks for inland waters, where direct sea cocks/ holding tank approach you suggest are not; at least that has been our experience. Yes, yes, its the same regardless but not with the various harbor authorities that might inspect your boat while in their jurisdiction.
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Old 13-06-2016, 10:19   #12
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Re: When are vented loops required?

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Y valves are accepted by the environmental folks for inland waters, where direct sea cocks/ holding tank approach you suggest are not...
Bull....
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Old 13-06-2016, 10:32   #13
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Re: When are vented loops required?

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Bull....
May be bull to you, but we got nailed traveling through the Great Lakes on this issue five years ago. No direct discharge. Any discharge line that allows direct flow must be sealed off. Y valve with clamp will do. Do you really want to seal off a sea cock?

Basic requirement is that the discharge route through the hull must be disabled so it can not be easily used. Port authorities(harbor masters, coast guard, etc) use their judgement as to how well the "disabled" flow will prevent its use.

But if you really want to disable a sea cock, by all means go ahead.
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Old 13-06-2016, 11:19   #14
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Re: When are vented loops required?

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There are configurations that allow odors to backup from holding tanks to toilet - not a broad idea to add a vented loop in the outlet.
The joker valve in the toilet discharge will block any odors from the tank or toilet discharge line until it becomes so worn that the slit can no longer close.
However if the toilet only discharges into the tank no VENTED loop is needed. But if it's an uphill run to the tank or the tank is significantly more than about 6' from the toilet, a plain ol' loop in the toilet discharge line immediately after the toilet (iow, aim the discharge fitting straight up) that's higher than the tank inlet may be a good idea because it would only be necessary to flush long enough to push bowl contents over the top of the loop...gravity will get it the rest of way. Cuts way down on the amount of flush needed, which extends the number of flushes the tank can hold.

Substitute a sanitary Tee for the Y-valve.

Not the best idea unless the overboard discharge pump is mounted above the tank because a tee doesn't provide any way to shut off the flow of tank contents to service/repair the pump...which you never find out when a tank is empty.
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Old 13-06-2016, 11:29   #15
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Re: When are vented loops required?

"Any discharge line that allows direct flow must be sealed off. Y valve with clamp will do. Do you really want to seal off a sea cock?"

The closed seacock serves the function of sealing off the direct flow. I have no safety issue with locking a sewage discharge seacock in the closed position.
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