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Old 09-10-2013, 08:03   #1
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Brilliant or Stupid?

After reading about various problems with macerating pumps. I am wondering if it is practical to pump out the waste tank with air pressure.
My thought was to connect an air pump used for mattresses, etc. to the vent line (blocking the exit) and using air pressure to force the goo up the pickup and out. My concern is that it will be difficult to get enough air pressure. The pipes are inch and a half.
Thoughts?
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Old 09-10-2013, 08:19   #2
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Re: Brilliant or stupid?

Better make sure your flapper and joker are up to it. Would hate a backflow accident. Guess a shutoff would stop that possibility.
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Old 09-10-2013, 08:27   #3
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Re: Brilliant or stupid?

That is what we do. We added a dip tube to the line from the 'Y' valve in the holding tank. I used a 'Y' valve that can be turned such that the overboard seacock is connected to that dip tube and the line to the head is blocked. I cut the vent line and added a barbed fitting so that I can quickly connect my low pressure electric air pump. The 2.5 psi air pressure empties the holding tank in one minute and 45 seconds. After I empty the holding tank I turn the 'Y' valve to overboard discharge. Oh course this is only done offshore in deep water.
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Old 09-10-2013, 08:34   #4
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Re: Brilliant or stupid?

Quote:
Originally Posted by jeanathon View Post
After reading about various problems with macerating pumps. I am wondering if it is practical to pump out the waste tank with air pressure.
My thought was to connect an air pump used for mattresses, etc. to the vent line (blocking the exit) and using air pressure to force the goo up the pickup and out. My concern is that it will be difficult to get enough air pressure. The pipes are inch and a half.
Thoughts?
you can use a pump that is a bellows type. i believe they are more reliable.
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Old 09-10-2013, 08:42   #5
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Re: Brilliant or stupid?

It would make me very nervous to pressurize a holding tank. One clamp or hose lets go and you've got a really nasty mess on your hands (and all over the boat). Happened to a friend of mine. Fortunately he wasn't by the tank when it blew up, his girl friend was. I think they may be back on speaking terms a couple of years later.

Mine is set up to gravity drain from the bottom of the holding tank with a Y that selects down to the through hull or up to the deck pump out.
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Old 09-10-2013, 09:09   #6
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Re: Brilliant or Stupid?

Install an above-water holding tank with a valved throughhull just above the waterline, and let gravity do the same thing. Keep it simple.
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Old 09-10-2013, 09:17   #7
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Re: Brilliant or stupid?

Quote:
Originally Posted by skipmac View Post
It would make me very nervous to pressurize a holding tank. One clamp or hose lets go and you've got a really nasty mess on your hands (and all over the boat). Happened to a friend of mine. Fortunately he wasn't by the tank when it blew up, his girl friend was. I think they may be back on speaking terms a couple of years later.

Mine is set up to gravity drain from the bottom of the holding tank with a Y that selects down to the through hull or up to the deck pump out.
Reminds me of a time when I was a crewman on a new 90 foot motor yacht.

During our summer cruise, I noticed that a plumbing elbow on the pressure side of the (very large) macerating pump had developed a crack. I phoned the builder of the boat and in spite of the weakness of the design, they sent us another exact replacement elbow.

No problem for the rest of our season.

Just after I left the boat, the owner arranged for the builder of the boat to do some winter work. During the passage back to the factory the very same engineer who stubbornly sent the same crappy (pun intended) replacement elbow decided to empty the holding tank while crouching directly in front of his creation......

I was saddened to hear of the coating of **** and toilet paper that permeated the absolutely immaculate, everything white, eat off the bilges - engine room.

I was very happy that the man who almost drowned in the ensuing deluge was not me.

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Old 09-10-2013, 09:29   #8
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Re: Brilliant or stupid?

Quote:
Originally Posted by skipmac View Post
It would make me very nervous to pressurize a holding tank. One clamp or hose lets go and you've got a really nasty mess on your hands (and all over the boat). Happened to a friend of mine. Fortunately he wasn't by the tank when it blew up, his girl friend was. I think they may be back on speaking terms a couple of years later.

Mine is set up to gravity drain from the bottom of the holding tank with a Y that selects down to the through hull or up to the deck pump out.
Do you have an electric head or other macerator to bust up the waste, esp. toilet paper, before it is pumped into the holding tank?
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Old 11-10-2013, 07:04   #9
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Re: Brilliant or Stupid?

Quote:
Originally Posted by Roy M View Post
Install an above-water holding tank with a valved throughhull just above the waterline, and let gravity do the same thing. Keep it simple.
Unfortunately I do not have the space above the waterline.
I am trying to keep this boat as simple as possible, but don't have that option.
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Old 11-10-2013, 07:36   #10
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Re: Brilliant or stupid?

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Do you have an electric head or other macerator to bust up the waste, esp. toilet paper, before it is pumped into the holding tank?
Manual head, using the integral, manual pump, no macerator. However in the interests of full disclosure I have not used this system yet as the boat is not back in the water. It is based on a similar system on a previous boat and identical system on a friend's boat, both of which worked without a hitch.
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Old 11-10-2013, 08:16   #11
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Re: Brilliant or stupid?

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Originally Posted by Cowboy Sailer View Post
That is what we do. We added a dip tube to the line from the 'Y' valve in the holding tank. I used a 'Y' valve that can be turned such that the overboard seacock is connected to that dip tube and the line to the head is blocked. I cut the vent line and added a barbed fitting so that I can quickly connect my low pressure electric air pump. The 2.5 psi air pressure empties the holding tank in one minute and 45 seconds. After I empty the holding tank I turn the 'Y' valve to overboard discharge. Oh course this is only done offshore in deep water.
....it was a hot sunny day... suddenly there was a strange pffft noise and the inside of Cowboy Sailors windows all went brown.
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Old 11-10-2013, 08:41   #12
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Re: Brilliant or Stupid?

I used that system for years, no problem. Just make sure everything is in good shape!
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Old 11-10-2013, 11:57   #13
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Re: Brilliant or Stupid?

I have have no problems with my standard head and maceration discharge pump on my current boat except for when the pump decided to just die (it didn't just stop but I could tell it was getting ready to so replaced it before it did).

My last boat had an electric macerating head with diaphragm discharge pump and it also worked just fine.

I think doing something weird like trying to use air pressure to blow out you tank is just making something simple into something hard to just switch 1 set of "issues" for some unknown one.

One of these days I will write up what happens on a submarine when the discharge line for the tank that blows out with air pressure clogs up.
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Old 11-10-2013, 12:11   #14
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Re: Brilliant or Stupid?

Quote:
Originally Posted by Roy M View Post
Install an above-water holding tank with a valved throughhull just above the waterline, and let gravity do the same thing. Keep it simple.
Yep best I had worked that way and was simple and flawless. My tank was long and tall. Some on this forum have not had as good results trying this so I dont know what makes a good setup from a bad setup.... but suspect a long tall tank helps. (more head) My exit was well below the waterline.
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Old 13-10-2013, 07:42   #15
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Re: Brilliant or Stupid?

First, any blockage in exit lines will "pump up" the tank like a balloon until it cracks.
Second, you should have a vent line to the tank that will need to be closed in order to pump the tank, or your air pressure will flow out the vent.
Third, since you will not be macerating, the TP and feces will try to discharge in larger sections. This will create more mess in the water and will probably result in a blockage somewhere in your discharge line.
I do not think this is a good idea.
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