Installing a macerator pump

[Omatako]

My boat has two heads, both with bag-type black water tanks, neither has any way other than vacuum pump-out to empty them. So I have started installing macerator pumps on both, actually the one installation is pretty much done. But is was a heck of a job and I'm not looking forward to undoing any of it.

This is how I piped the thing up:

In reality the only changes are the pipes to and from the new pump and the Y fittings into the vacuum pipe and into the seacock discharge line. The "heck of a job" included a complete re-pipe and a new Y valve.

In a quick test it seemed to work OK but I wondered whether I need any one-way valving to stop unwanted "stuff" appearing in the bowl? For example, a few barnacles in the skin fitting and enough pressure could result to push back up the yellow line into the head. My guess is switching the Y valve would deal to that but what if someone forgot to do that?

Another thing that I discovered in the quick test is that the exit fitting from the bag is not at the bottom and as soon as the level in the bag (I filled it with water to test) drops to this fitting, the pump starts to cavitate which with these pumps is a no-no. That means a significant percentage of the contents will not be pumped and will lie in the bottom of the tank. The vacuum units draw everything out, flattening the bag in the process.

I also noticed that when the pump ran and the level got down to the exit fitting, the back "skin" of bag was drawn onto the fitting effectively blocking it off. I wondered whether repositioning the bag to stop this happening would help the pump get more contents out.

Any comments?

Andre

[theartfuldodger]

Have a question in each head where does the sink drain straight out the hull, you are probably wondering why I'm asking this, but depending on your answer, may have a very simple fix for you

[Ilenart]

Omatako,

one thing I would suggest is be careful in leaving liquid in the bag. I have a similar system I installed last year (without the Y valve) & I am having problems emptying the bag completely. Lately there is a smell coming from this compartment and I cannot locate any leaks in the system . So I am wondering if the smell is coming out of the bag. What I am going to try in future is to flush the bag a couple of times before I leave the boat for extended periods so any liquid remaining is mostly sea water.

I also have the same problem when the bags almost empty that the back skin gets drawn in. A couple of times I have lifted the edge of the pipe when the pumps running and that sucks out a bit more.

My outlet fitting is on the right hand side so I normally empty the tank on a port tack, which means the outlet is the lowest point of the tank. This definitely helps in emptying the majority.

Overall I have not been too happy with the "bag type" tank and I am wondering whether a "hard type" tank would be a better option in the long run. However the bag type was significantly cheaper so I am persevering with fine tuning "the system"!

One thing I noted on your diagram is no water inlet. Assume you have a saltwater inlet not shown?

[sailingdog]

One change I'd make to your system, to both simplify the plumbing and to make it more reliable is to eliminate the diverter valve and have the head pump directly into the holding tank. When you're out past the three-mile limit, you can always empty the holding tank instead of pumping the head directly overboard, so you're really not losing any capacity.

I would then put the diverter valve, which you removed from the head output line, in the holding tank output line, where you have the "Y". If you ever have to work on the macerator pump, having this diverter valve will make your life a lot simpler and help keep the mess to a minimum.

[Rodz47]

I am looking at the drawing and trying to understand the rationale behind putting the vent line together with a drain? I am not a plumber but for me it looks like your pump will be sucking air not sh...t. It sounds like cavitation also. Wouldn't be better if you install your vent in the upper portion of the tank??

Just a thought!

[sailingdog]

He said deck vent, he meant deck pumpout fitting.

Originally Posted by Rodz47

I am looking at the drawing and trying to understand the rationale behind putting the vent line together with a drain? I am not a plumber but for me it looks like your pump will be sucking air not sh...t. It sounds like cavitation also. Wouldn't be better if you install your vent in the upper portion of the tank??

Just a thought!

[artbyjody]

There is a decent illustration .. hope that helps.

[brak]

Тhat's kinda how I have it except I don't have a Y-valve - just a regular Y crossing. Gotta keep the deck fitting properly closed when using the macerator, but it does seem to work well even that way (less than 3 minutes to empty over 30 gallons of liquid in a tank).

[Omatako]

Let me respond one at a time:

Brak - the Y valve allows me to positively direct the black water where I want it. As mentioned below, I don't want everything automatically directed to the tanks.

Jody/SD - the layout you have provided (thanks for that) is the same as suggested by SD inasmuch as everything pumps to the holding tank. That may be best in the US but "anywhere else" in the world, within a relatively close proximity to the shore you are allowed to pump macerated black (no solids) water to the sea. In NZ that limit is 500 metres. And especially when we're at sea proper, we rather pump black water directly to the sea and not to a holding tank. Hence the position of my Y valve.

SD - as far as being able to effect repairs without getting oneself immersed in black water, that's really a matter of wash, wash, wash before disassembling. I just did that and not too terrible.

Rodz47 - SD got in 1, that's where the pump-out connects and it is of course a good seal so no problem.

Ilenart - Yes leaving juice in the bag bothers me too. I've just replaced all the pipes because some of them were transmitting odours. I think that the bags will start to do the same after a time. I guess it will become a ritual of flushing the bags with volumes of water and pumping it out before leaving the boat. And, yes the water in isn't shown, that's really a given. I was more trying to debate the outlets. Solid tanks are just too big a job, I'd rather replace the bags periodically

Dodger - my basins drain through their own skin fittings but they're above the water line so not really a 1st choice for black water . And besides, a backfeed into the basin would probably irritate my wife a little especially while she's cleaning her teeth

One of my concerns is the back-feed and more I think about it the simplest solution would be to fit a joker valve into the yellow line (my diagram).

Thanks for responses, always valuable.

Andre

[artbyjody]

Originally Posted by Omatako

Thanks for responses, always valuable.

Andre

In the states we are more stringent on how systems can hook up... Prior to - the regulation - a y-valve was ok prior to the holding tank to discharge overboard...hence why the drawings reflect the y-valve after the holding tank - it appeases the gods that inspect to make sure at least US vessels meet our laws for discharge of waste....having one prior to the tank and before the head - here in the states we are presumed guilty of not abiding by the rules...