Black water system

J

Jamesuk

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Hi

We are currently having a black tank re-install, the local expert says we should dump the Y valve system and go with a direct "to tank" flow (vacu-flush) this being the standard in new yachts??

What are your thoughts on the issue?
 
On my Grand Banks in the USA, where they take this subject very seriously, I had a Vacu Flush discharging directly into the holding tank with no Y valve. On the discharge side I had a Y valve so I could discharge the holding tank either to pump out station or to sea. The Y valve could be locked in position.
This system's legality is open to question but was never challenged. I think it is the system most likely to survive the push towards preventing all overboard discharge within territorial waters the longest. Eventually, many years from now we hope, it will be necessary to carry adaptors and hoses to allow you to discharge the holding tank via the pump out port when off shore because no country is going to allow options such as Y valves even if they are lockable.
 
I fully agree with your local expert. Diverter valves are a PITA and quite unnecessary. Go for the straight-through method, far less complex and almost totally reliable.

Heikell recommends this method, as do many others.
 
thank you for your reply, we are currently in fort lauderdale undergoing some re-invention of the wheel stuff. The old systems used a macerator pump that had a feed going up which caused the piping to hold sewage (odors) we currenlty have the option to flush directly overboard with vacu flush or into the tank, we also can discharge from the tank overboard or pumpout (spagetti junction)

We are thinking (I) that when we hit France we may get nailed
 
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I fully agree with your local expert. Diverter valves are a PITA and quite unnecessary. Go for the straight-through method, far less complex and almost totally reliable.

Heikell recommends this method, as do many others.

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Vyv,

What are your thoughts on the necessity of going with a 2" outlet for this system?

Andy
 
When you get to France, pump outs will be as rare as hens teeth! The most popular systems are gravity holding tanks with a shut off valve to close the outlet when in a marina. The pumpout is through a pick up pipe in the tank and a pump out fitting on deck (connected by a hose of course!) Good designs have an inspection hatch immediately above the outlet so that you can clear (rare) blockages. See the Tek Tanks website for schematic layouts.
 
I can't see why a 2" outlet would be necessary, assuming normal use of the toilet(!) A joker valve is a remarkaby efficient device at breaking up solid waste and it is very rare that anything bigger than about 20 mm diameter is discharged overboard. The majority is little more than a suspension of very fine particles. Bearing in mind that I cannot advise in cases of severe constipation I believe the normal 1.5 inch (38 mm) outlet to be perfectly OK. All the black water tanks in my Vetus catalogue come with 38 mm outlets, including the gravity drain one.

The best systems I have seen position the pump-out tube immediately above the outlet so that rodding can be carried out from on deck if a blockage does occur. I'm not sure how many commercial tanks have this feature but the Tek-tanks custom ones I have seen described do so.
 
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I can't see why a 2" outlet would be necessary....(snip)

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It was a recommendation by Tektanks to avoid blockages in a gravity system. Pleased to hear that you seem to manage OK with the normal 1.5" outlet (err.. tank outlet, that is /forums/images/graemlins/smile.gif ).

Changing the seacock/thrugh-hull to 2" would be an additional ~£150 on the cost of parts to install a holding tank, and has been putting me off a it - not to mention the physical size of a 2" ball valve.

I'm planning to do as you suggested, and put a dip-tube immediately above the outlet, but will probably just plug this off for now (and not bother with pump-out at the moment). I also plan to fit a (plastic) valve at the holding tank exit, so that the contents can be held back in the event of problems at the seacock.

All I've got to do is relocate the 240V breakers, 'leccy meter, wire up the relocated battery charger, turn the fuel tank around and remove the cockpit locker shelf, and the way should be clear to put the tank in... /forums/images/graemlins/ooo.gif

Andy
 
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