12 Meter Sanitation Overhaul - Relo of Vacuum Tank

[tcollins2]

The 12 M that I bought last year has a Vacuflush system. The vacuum tank is located at the foot of the bed in the bow and can only be accessed via a 12x12 hatch. My project was to replace all the sani lines since there was a significant smell that couldn't be covered up any longer with fragrance. One of THE worst jobs out there. Turns out the hoses were all original since the two lines that went up front to the tank were zip tied together and then that zip tie was screwed into the stringer. Two locations. This could only have been done at the original build. I had to attach a hack saw blade to a 6-foot stick and cut the hoses loose. These hoses were so incredibly rigid due to age. I cannot believe they were never replaced. Since I had removed the vacuum tank from the bilge to get the hoses off, I cleaned it up and notice some of the tank was white and some of it was light brown/beige. Then I saw stress cracks in the middle ring that joins the two halves of the tank. I think I need a new vacuum tank as well. I read on the Dometic website that the outlet of the tank MUST be pointed down. This tank was actually rotated 90 degrees with the outlet facing forward. This actually traps a certain amount of sewage in the vacuum tank forever. The stress cracks are coincidentally on the bottom half of the tank where the sewage sat. I unscrewed the vacuum switch to see if that was in ok condition becuase they are about $200 I then noticed that since that sewage sat in the tank for about 25 years it created this "concrete" that I couldn't remove. The smell of the tank is stronger on that area of the tank than on the top of the tank. I didn't think those vacuum tanks could permeate odor, but they sure can.
Has anyone ever relocated their vacuum tank? I'm going to put in in the cabinet where the central vacuum is located. Easy access, makes the hose runs much shorter and that cabinet doesn't get used at all since it's a PITA to remove those curved cushions if you want to get in there. I need to splice a wire from the connection in that 12x12 and run it back to the new location.
The tank will still be downhill of the toilet but not as much as putting it below the floor where it was.
Anyone see any flaws in this relocation?

I wanted to attach some pics, but it won't let me. "Sorry, the board attachment quota has been reached"

[Big D]

The vacuum generator system must be up hill from the holding tank. This way, the lines to the holding tank will drain naturally and not leave any waste sitting in the lines. If doing this is impractical in your application, then waste will always sit in that line. In such a case, to overcome the possibility of permeation again in the near future, use rigid line from the vacuum generator to the holding tank as rigid line such as ABS won't permeate. From the toilet to the vacuum generator doesn't matter as everything should be evacuated during a flush and the lines left empty.

[tcollins2]

I bought a 50 foot roll of Shields 105 Poly X Sanitation Hose, it has a lifetime (as long as it is my lifetime) warranty against odor permeation.
I think I'll be ok with that. The toilet ball valve is about 6 inches higher than the future location of the vacuum tank, that would go slightly lower to the vacuum pump and that is level with the top of the holding tank.

[Big D]

That's a very good hose. Keep in mind, that if the line is flexible, it's permeable. The more flexible it is, the more permeable it is. How long it will take to permeate depends on this and its construction. Compared to the cheaper hoses, you'll find that the Poly X is less flexible. Along with the materials used, that's one of the ways to increase the length of time before it starts smelling again. There have been some recent improvements to overcome this but technically this still seems to be the case in spite of the claims. Even with this technology on the market, Sealand still recommends rigid hose in areas that will have standing waste. For all intensive purposes though, you'll get quite a few years with no worries using that hose.

[P-Dogg]

From the toilet to the vacuum generator doesn't matter as everything should be evacuated during a flush and the lines left empty.

I have not found this to be the case. How do I know? When I installed my two new vacuflush heads last summer I used clear PVC pipe from the man's department store -- McMaster.com, which even at $75 for 10 feet is cheaper than the good sanitation hose -- I did not spring for clear fittings, plus they don't come in long-radius style). My forward head has 3 long-radius 90 degree elbows and about 15 feet of combined hard PVC and two short lengths of flex at each end (the lifetime dark gray wire-reinforced stuff). I believe the specs in the installation manual say no more than 50 feet of run and 10 elbows, so I am way under what is allowed. Vertical lift is about 16" -- again well under what is allowed. While the bowl is completely cleared during a flush, the lines, even 3' from the toilet, are not. And if you think about it, it makes sense.

Consider the volume of the vacuum tank, which operates at 10 in. Hg, which means it is 2/3 full of air (I installed vacuum gauges on the top of each tank for future troubleshooting purposes). And then consider the volume of the lines (which, by the way, contribute to the effective size of the vacuum tank for bowl evacuating purposes), and how long the seal at the bowl is broken when you flush the toilet. There is just not enough "vacuum energy" available to get everything out of the bowl, through the pipes, and into the vacuum generator in the two or so seconds it takes to flush, plus, the volume of the lines is greater than 1/3 the size of the vacuum tank, so not everything can be removed from the pipes when you flush.

[Big D]

I can see how some of your statements would apply but in a properly sized, installed, and properly operating system, I have yet to find any waste on the vacuum side unless there is a clog in the system. You may find a little water that got in from leaving the pedal down too long but no waste. Have I seen waste on the vacuum side without a clog? absolutely but there is usually a logical explanation for it that boils down to an installation related fault. The key here is properly sized, installed, and operating properly.

Things have changed over the years, the biggest installation changes is that each toilet must have its own vacuum generator, line routing, materials used, proper hardware, and positioning. This was not the case in older installs to their detriment, and of course don't expect to find optimal installs from the boat manufacturer, they never adhere to third party OEM recommendations for installs such as this.

I'm not sure what you mean by "2/3 full of air" under a vacuum. Actually, the vacuum generated is enough to do what it needs, and does only take about a second for it to evacuate the system, it needs to. It must empty the system before the pedal is let go or equalization takes place, while also forcing liquid and large solids through the funnel which serves to macerate the solids while they're being forced through. This requires more energy than one might think is available from the vacuum that's generated but that amount of vacuum is actually pretty powerful. If there wasn't enough vacuum, none of this would happen nor in the short amount of time required for optimal performance.

I've worked on many systems, there's a huge difference between a good install and one that's not.

[Big D]

I forgot to mention another important aspect of the equation acting on the system; atmospheric pressure. At sea level, 14.7 lb per square is acting on the water in the bowl. The combination of that and the vacuum is a lot of force for this task. Once the barrier between the vacuum and atmospheric pressure is breached by opening the ball, that pressure rushes in at a high speed to fill the void. Compounding the speed at which the air rushes in on its own to fill the void is the force of the vacuum pulling it along if you will. I'm sure there's a formula for calculating how fast that happens but for all intensive purposes, it's extremely fast, that's why you can get away with a 50 foot run in just 1-2 seconds of pushing the pedal to allow air in for displacement.

By the way, within reason (50 foot rule), the volume in the lines doesn't matter since the entire run is under vacuum. The only volume that matters is the amount of waste in the bowl along with about 1.5-2 liters of water. As long as that volume will fit into the vacuum generator, that column of waste will be carried by the equalization wave if you will to the tank with vacuum on its leading edge and pressure on its trailing edge.

I may have used the wrong choice in words with respect to the vacuum line construction not being important, it is a flexible line after all that will eventually permeate but in comparison to the discharge side of the system that typically has standing waste in it, the vacuum side should take much much longer to become problematic. The odours from the other side of the system should precipitate hose replacement (if acted on) long before the vacuum side gets really bad.

As mentioned before, you're likely to have some water in the vacuum side from leaving the ball open for too long which is common operator error, and it will mix with what's coated on the hose wall but it should not be actual waste. If there is waste there, or 3' of water still in the line, there's something wrong.

Apologies for being long winded. I'm sure there's an easier way to explain the physics but this is my way. Hope it makes sense.

[tcollins2]

Based on what you're stating and what I've read and heard from the tech at dometic, I think my relo will be just fine.
I was surprised to know the vacuum tank can be up to 50 feet away. My old run from bowl to vacuum tank was about 15 feet, now it will be about 5.5 feet. Less hose, less problems. No sags or loops either.
Thanks for your input.

[P-Dogg]

No need to apologize for a long post Big D. You always have a lot to contribute, and that is best done through good, ample communication. It is what makes this forum useful.

I'm not sure what you mean by "2/3 full of air" under a vacuum

A complete vacuum at sea level equals about 30 " of Hg. The tank vacuum-sensing switch is set to shut-off the pump once it pulls 10" of Hg. That means that the air in the vacuum tank is not completely evacuated, only about 10/30 is evacuated, which leaves 20/30 of it in there.....

I don't have time now to make a considered response to the other points, but will later. One question for you Big D: Have you ever seen any head system plumbed in clear pipe?

[Big D]

.....Have you ever seen any head system plumbed in clear pipe?

Yes, at Sealand Vacuflush training. They had a complete system set up that way for demonstration so we can see what actually goes on, much as I described above.