When are vented loops required?

[Terra Nova]

Originally Posted by peghall

...

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.

Since you can still evacuate the contents of the tank, through the deck pump-out, I see no reason to add one of the most clog-offending devices in waste systems: the Y-valve. And it is still possible to install a shutoff valve at the tank discharge.

[Cheechako]

Originally Posted by reed1v

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.

Not my experience. either way, it must be "locked" with something.

[Cheechako]

Originally Posted by peghall

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.

Good point on the pump. Then again, I aint going in there 'til it's all empty and flushed with fresh water!

[Terra Nova]

I had just completed the installation of a new holding tank system. The owners were about to leave, for a few days at the islands, and asked me what they should do if the holding tank filled up. I said "Stop eating immediately!"

[tbosch]

Originally Posted by Terra Nova

Since you can still evacuate the contents of the tank, through the deck pump-out, I see no reason to add one of the most clog-offending devices in waste systems: the Y-valve. And it is still possible to install a shutoff valve at the tank discharge.

With a TEE instead of a y-valve, are you relying on the o-ring in the pumpout deck fitting for the overboard discharge pump to work? It seems like it could pull air and not blackwater if there deck fitting wasn't in great shape.

Interesting thread. This project is on my list, unfortunately...

-Todd

[Terra Nova]

Originally Posted by tbosch

With a TEE instead of a y-valve, are you relying on the o-ring in the pumpout deck fitting...

Why not? This isn't the Apollo program.

[nelsmay]

There's a good article in the latest edition of Sail (July 2016) magazine on this exact subject. Graphic provided is very clear.

[tbosch]

Originally Posted by Terra Nova

Why not? This isn't the Apollo program.

Ha! True dat!

[HopCar]

A little thread drift. There were two companies competing for the Solid Rocket Booster contract for the Space Shuttle. Morton Thiokol and Aerojet General, both in the rubber business.

Morton Thiokol won the contract with their boosters being able to be transported by train because they were in segments. The segments were stacked to build the booster at the Cape. The segments were sealed with the infamous O-rings.

Areojet General would have built the boosters with a solid case in South Florida and barged them to the Cape. Solid case equals no O-rings. No O-rings equals no Challenger explosion.

Aerojet built a large facility in the Everglades near the entrance to Everglades National Park. It was abandoned in the late sixties. I've been to it and it is really spooky.

They tested several engines there and they left the last one in place after firing it.

It's still there. It is in a deep concrete hole that was covered by a movable building. The building has now been removed and the pit covered by concrete beams.

[SV Bacchus]

Originally Posted by HopCar

A little thread drift. There were two companies competing for the Solid Rocket Booster contract for the Space Shuttle. Morton Thiokol and Aerojet General, both in the rubber business.

Morton Thiokol won the contract with their boosters being able to be transported by train because they were in segments. The segments were stacked to build the booster at the Cape. The segments were sealed with the infamous O-rings.

Areojet General would have built the boosters with a solid case in South Florida and barged them to the Cape. Solid case equals no O-rings. No O-rings equals no Challenger explosion.

Aerojet built a large facility in the Everglades near the entrance to Everglades National Park. It was abandoned in the late sixties. I've been to it and it is really spooky.

They tested several engines there and they left the last one in place after firing it.

It's still there. It is in a deep concrete hole that was covered by a movable building. The building has now been removed and the pit covered by concrete beams.

Ya gotta wonder, was it the ability to transport by train or was it low bidder got the contract?

Back to the thread:

We still don't own but our eyes are on a 97 Leopard 45 model and I fully intend to explore this issue completely as, I believe, the holding tanks are above the head allowing for a gravity drain. Simplicity with a lack of odors and avoiding the dangers Peg mentioned of having to service a pump and the, Ohhhh Ugh, damn mess that might come with it.. That is what I will be striving for!

[ggray]

Peggie, I am about to do just that: holding tank (with two vents !) below the waterline, up a foot or so to manual black water pump, then down to seacock. I hadn't wanted to install a vented loop ahead of the seacock, but worried that it was "required".

So you are saying it is not necessary? I would, of course, ensure that it was closed except when pumping.

Originally Posted by peghall

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.

[peghall]

You are only referring to the discharge line from the TANK, not from the pump...right? If so..and if the pump is mounted well above the waterline AND if you keep the seacock closed except when dumping the tank, you can get away without a vented loop in that line.

But...if any part of your toilet is below waterline and there is no vented loop in the flush water intake, you definitely one there. It goes between the pump and bowl, needs to be 6-8" above waterline at any angle of heel, which on most sailboats puts it 2-3 FEET above the bowl...so will require replacing the short piece of hose the mfr used to connect the the pump to the back of the bowl with new hoses long enough to install the loop...which, btw, is 3/4"

[ggray]

Peggie, if I understand your question, I was wondering about (hoping not to need one) a vented loop between the black water pump and the seacock/thruhull.

The tank top is almost 2 ft below WL, the pump would be perhaps 6"-8" below WL, and the thru hull almost 2 ft below WL.

I don't understand why it would make THAT much difference if the pump is above WL in this scenario. Sure, there would be less pressure against the check valves in the manual pump, but the possibility of syphoning would be there regardless, absent a vent.

I was hoping you would give me an "Easy Button"! I would certainly plan on closing the thuhull after pumping; besides, any syphoning could only fill the tank, maybe 25-30 gal. There would need to be another failure.

Regarding an anti-syphon on the sea water intake ( bowl rim made 1" to 2" below WL on a catamaran, I can always add an AS vent, but I'm thinking that just a loop above the WL that close to the exit of that line, with an ID that large, the line is essentially vented anyway. I'm told there are two check valves in the PH II that restrict this flow also.

And not to add to the length of this post, but I have seen the installation of two PHII heads in a keel boat from a respectable manufacturer, with no vented loops here. Must be 1' - 2' below WL, not heeled. 16 year old boat, not sunk yet. I want to delicately address this with the owner.

[Terra Nova]

Originally Posted by ggray

...The tank top is almost 2 ft below WL, the pump would be perhaps 6"-8" below WL, and the thru hull almost 2 ft below WL....

Install a vented loop.

[bobmcd625]

Great topic as I am in the process of reconfiguring my MSD system in exactly the way described by ElCapt Drew. I have two questions: is the vented loop between the bowl and the pump really necessary? The inlet to the bowl tees off the wash basin discharge line. Does that provide the vent?
Second. I plan on a Y valve after the tank to switch from pump out to shore or pump out overboard (via a Whale Gusher). Does this Y valve have to be "lockable"?
Thanks for all the good tips in this thread.