macerator pumps

[smileygirl]

I want to fit macerator pump in line with the existing pump out hose, Is it OK to pump out into the sea toilet exit below the waterline? also does macerator pump need to be lower down than the base of the tank ?? and (finally) anyone recomend a pump make/model ?

 

[terryw]

My current macerator is on top of the holding tank, and previous ones have been anywhere from under to mid way, so I would suggest that the location is not too important. In all cases the outlet has been below the waterline (you may have a problem with air locks if the outlet is above the waterline, not to mention the possibility of brown streaks on the hull)

 

[jfm]

Macerator needs it's own thru hull seacock discharge. You cannot Tee it into an existing discharge hose (if that's what you were asking?) else it will pump its contents the wrong way up the line and fill your toilet bowl with [nasty stuff]

Height depends on priming characteristics. Most have decent flexibility so the macerator pump could be up to say a foot above the holding tank. check the specs. But probly better to mount it lower than the top of your holding tank, especially if you want it to prime when your tank isn't full.

As to which is the best model of macerator pump, better wait till Headmistress chimes in. She is a pro installer so has seen all the products available and can compare

We use this one and it's ok, nuthin special good or bad, but I couldn't say whther it is the best or the worst or in between
http://www.johnson-pump.com/JPMarine/default.htm?page=/JPMarine/Lavatory_systems/Macerator.htm

 

[HeadMistress]

You can tee into the existing toilet discharge thru-hull, provide that thru-hull isn't too far from the tank....it's done all the time. Just make sure that the y-valve in the toilet discharge line is directed toward the tank when dumping the tank...'cuz if it's open to the thru-hull, jfm is right...some of the waste from the tank can make a wrong turn and head for the toilet instead of going overboard. The closed y-valve will block it. It's also necessary to install a y-valve--not just a tee or wye--in the pumpout line...and that it be kept closed to the macerator except while dumping the tank...if it's open to the macerator and thru-hull, there is a risk of filling the tank with sea water while underway. The macerator will only slow it down, it won't block it.

As for where to put the macerator, the installation instructions are pretty clear about the max distances--linear and height--from the tank that it should be to allow it to prime in time to prevent damage to the impeller from running dry. Mounting it above the tank may eliminate the need for a vented loop in the line to the thru-hull if the tank or any part of it is below the waterline. But whether you use the existing toilet thru-hull or install a new one, it should be below waterline...neither you nor your guests/crew will enjoy seeing/smelling a tankful of waste coming out the side of a boat!

Johnson and Jabsco macerators are comparable quality, so it doesn't matter which you choose. However, IMO an electric diaphragm pump is a better choice than a macerator because diaphragm pumps can run dry without harm and rarely require any service or repair...and few things are more "fun" than being forced to service a macerator at sea when the tank is full (another reason to put a y-valve in the pumpout line instead of just a wye or tee fitting...so you can close off the flow of waste to the macerator). Diaphragm pumps cost a bit more, but it only takes a couple of replacement impellers for a macerator to make up the difference. And you can expect to replace impellers, 'cuz not only can running dry destroy an impeller, but if the macerator isn't used for a while, the impeller can become stuck to the inside of the housing...if it's stuck tight enough, start up will crack a vane.

Whether you opt for a macerator or diaphragm pump, just be sure to follow ALL the installation directions for installing it carefully. Wiring is even more important than plumbing. I would run a new circuit for it, so that nothing else that's on when you run it can pull power away from it (low voltage will damage a motor), also so that it has its own breaker which can be left off except when you do need to run it. It may not be as convenient to have to open and close y-valves and seacocks, and turn breakers on and off to dump a tank instead of only pushing a button...but the more you have to consciously do to dump a tank, the less likelihood of accidentally doing it with undesirable consequences.