How much vacuum does it take

Guest · Dec 7, 2010

Pump out

Our local system has a gauge and I'm trying to visualize what it says, but I think it is around five to seven pounds. I've also noticed that many of the commercial systems installed by our various marinas take some time to build enough pressure to vacuum the tank, especially if it has been idle for a period. Here they recommend that you first start the system by dropping the nozzle into the water before inserting it into the deck pump out fitting.

Terry Cox

Weasel · Dec 7, 2010

Re: Pump out

Guys:

Vacuum is measured in inches of water or inches of mercury. You pull a vacuum on a tank that is not vented and you will collapse the tank. I would guess the range for the pumpout stations are 7-12" water column. (Having a pump that would pull inches of mercury would collapse a tank as well as lines). Not trying to answer the question just trying to help define the question. The pump out station unit should be clearly marked with the range of vacuum. Shop vacs are powerful, but still very low in inches of wc.

Weasel

Steve Dion · Dec 7, 2010

Honestly I have never seen a pump out station with a gauge. The systems have either pumped the crap or not. Our pump out stations normally have a sight tube so you want watch the "STUFF" pumping out, but that is it.

They either work or they don't.

petersea · Dec 8, 2010

If the local pump out station is pumping out everyone else boat I would suspect the problem is your boat not the pump out station. I would suspect you are not creating a "vacuum" due to a air leak in your boat or another possibility it that your tank pick up is clogged or broken. Most of the newer tanks have a pick up tube so it empties from the bottom up rather then a pump out connection on the bottom of the tank. Not a very pleasant job but you will need to to some diagnosis on your system. Don't know how much vacuum is needed in terms of a gauge reading but it will not compare to your shop vac as to strength.

kloudie1 · Dec 8, 2010

Well, the lift required of the pump is how far it has to lift the stuff to get it out of the boat.. so if your tank is at water level and the pump is on the dock .. the pump might be 5 feet above the tank level.. So the pump has to generate 5 feet of lift, 60” of water or since one inch of mercury is about one foot of water, 5 inches of mercury will be required.. now you have to add the pressure losses in the pipes and hoses, so in this case, the pump would have to generate about 6” of mercury (about -3psi, or 12psia) .. If the pump is at tank level, then it has to generate enough lift to get over the highest hose loop to get going .. Pete’s observation is a good one.. if the other guys are getting pumped out, then you probably have a collapsing hose or some other restriction.. Most pump-out pumps are diaphragm pumps and can generate 15-20 feet of lift.. (a half to two-thirds of an atmosphere)

Ron20324 · Dec 8, 2010

kloudie1 said:
Most pump-out pumps are diaphragm pumps and can generate 15-20 feet of lift.. (a half to two-thirds of an atmosphere)

Seems to me the Annapolis pumpout boat had a guage, but I don't recall the numbers. To compare, doesn't a dingy pump do about 3 psi

Peggie Hall HeadMistress · Dec 8, 2010

You don't have enough information yet.

Petersea has raised an excellent point: is yours the only boat that your marina's pumpout can't pump out? That's the first thing you need to find out.

You pulled the vent line off the tank, but did you check the tank fitting to see if it was blocked by buildup? That's very common on sailboats due to waste spilling into the vent when the boat heels.

You cleaned out the tank and apparently rinsed it out, but if you only used the shop vac, how can you be sure that the tank discharge line or pickup tube isn't blocked by the same glop (sludge) you vacuumed out of the tank?

You say that only liquid waste went into the tank (which, btw, is silly 'cuz solid waste is 75% liquid to start with and dissolves VERY quickly in water, so it can't cause a blockage)...but what about TP? Quick dissolve TP can be flushed without any problems--and should be the ONLY kind of TP made available to guests...but if you had guests aboard and didn't make sure to tell 'em that NOTHING except the TP provided can go into the toilet, can you be sure that no one flushed a wet wipe or tampon...or even any premium "extra soft, extra strong" TP that YOU may be taking great care to put in the trash can, but they weren't?

So you have quite a few possibilities to eliminate before you can be sure that the problem is the pumpout and not an issue on your boat.

catsailor · Dec 8, 2010

paiscool said:
Approximately how much vaccum is required to extract the contents od a holding tank.I suspect that the pump out is not sufficient for my boat and here is why.
Last year when I bought the boat,I had a problem where I couldnt pump the boat out.It turned out that the bottom 5 gallons of the tank had a thick goo.So I shop vacc'd the entire tank.I also have an airtight inspection port I installed so I could see inside the tank.When I finished emptying the tank last time there was no residue in the tank and I ran water in and emptied that too.Using the Shop Vac.
For this season,we used the head but only for Number 1.So when I open the inspection port,I can see it is a watery substance.
I went to pump out for the first time since then and nothing comes up and out.I removed the vent hose from the top of the tank to make sure there was not a blocked air vent,still nothing. I put my hand on the pump out intake and there is minimal suction.So my question is,what is the amount of suction I should have to empty a holding tank? Thanks

I'll ask a simple question; when you used the pump-out station, did you take ALL of the hose loops off of the holder and lay them flat on the dock, per the instructions? It is very tempting to leave the hose you don't need on the hanger.

The difficulty is this; the pump has to lift the water up the first loop, up the second loop, and up... and so forth. If each loop is 3 feet and there are 5 loops, that is an extra 15 feet of lift. This is only true when you start (lots of air in the hose) and is rather unique to vacuum applications. It is the reason fuel trucks can have a hose on a reel, but jiffy-john trucks do not. It would also explain why the shop-vac worked, why others are having no trouble, and why you had little vacuum.

Try again.

petersea · Dec 8, 2010

paiscool said:
If i used a Shop Vac at the deck fitting ,first of all would it suck the stuff up? Second, I would assume if I can put water in through the deck fitting that I could conversely suck it out.

I know there is traffic at the pumpout occassionally but I dont know if they were successful.The next question would be if some were successful could it vary by the distance from the pumpout desk fitting to the tank itself.I put my hand over the end of the pumpout,there was what I would say was very little suction.
Thanks

No not necessarily, If the pick up tube is broken or maybe cracked at the tank fitting water would still enter the tank but not necessarily vacuum out of the tank. The shop vac may or may not have enough "lift" to empty your tank from deck height. I would check to see if the shop vac can empty the tank from the tank fitting first then see if it can draw from the deck fitting but first use the shop vac to "blow" all the lines to make sure they are clear (including the vent). Also check all your plumbing to make sure there is not a valve or something open that may break the vacuum like an overboard discharge line and or macerator.

You appear to feel that you need lots of suction to vacuum the tank and that is not the case. I came across a similar situation when working on a system and though I had a bad pump because it was not creating a lot of suction but as soon as I filled the hose with water it was empty in two second and would pump out as fast as the hose would put it in. These type of pumps will move lots of water and not necessarily create lots of suction. Test the pump out pump to see if it will empty the pump out hose when filled with water. Or watch someone when they empty there tank to see if it operating correctly. You can remove the vent hose temporarily to test if it is clogged when doing a "test" pump out. Is there a filter in the vent line ?
Sometimes they will clog as well and prevent the tank from being emptied. Start at the tank and work towards the deck fill following all the hose and check any and all fitting. I guess the only good part about all this is your tank is ( I assume ) all ready emptied by you shop vac and now you are using just water or at least I hope that is the case ! ! Good Luck !

Peggie Hall HeadMistress · Dec 26, 2010

Well, you're narrowing down the possibilities

What about the tank vent? You haven't said any more about it since I asked in my previous post if you'd ruled out all the places for a blockage.

What kind of success or problems are others having at that pump out?

You need those answers before you starting ripping out any hoses.

Guest · Dec 26, 2010

Pump out problems

Just curious. If you were to fill the holding tank to the top of the deck pump out fitting with water and then pump it out with the marina system, what exactly happens, in detail? If the stand pipe in the holding tank is cracked say at the top of the tank, the marina system will extract water until it reaches the level of the crack where it will begin to draw air through the tank vent, assuming that the vent line is open.

Does the marina pump out system have a clear section of pipe just before the nozzle like ours does? This section of pipe will show some of what is going on with the system. Before I insert the nozzle into our deck fitting I will stick the nozzle into the water to confirm the system is drawing. Then I close the nozzle, insert it into the deck fitting and open the valve. If you were to do this what happens exactly? Does the marina system appear to lose its suction; in other words does the clear section of pipe behind the nozzle remain full of water or does it empty out and not fill back up again, which would indicate that it is drawing air?

Also, you referenced that you used the shop vacuum to blow out the vent tube. How do you know you blew it out? When our vent was plugged even city water pressure (60 psi) was not enough. I had to use a small screw driver at the through hull scupper to break the hardened crust before the line cleared. Now, after every pump out, I force city water through the tank vent scupper and I can hear and feel the water flowing back into the tank.

Terry Cox

Guest · Dec 26, 2010

pump out problems

Some puzzle. In an earlier post you said that your friend poured water down the deck fitting and you say water flow into the tank. That hose seems okay and not plugged. Our tank pump out hose connects to a stand pipe inside the tank; a bit different than yours, which connects to a fitting at the bottom of the tank.

The toilet should not be an issue here unless I'm missing something. If, as you say all the hoses seems clear, an air leak preventing a vacuum from building appears to be the culprit. As you say these systems are pretty simple, but as Peggie refers, replacing hoses at this stage, until you know the cause, might be a waste of time and money.

Terry Cox

Peggie Hall HeadMistress · Dec 26, 2010

No way the toilet is involved, but about the tank vent...

You said earlier that you pulled the vent line off the tank, but did you check the tank fitting to see if it was blocked by buildup? That's very common on sailboats due to waste spilling into the vent when the boat heels. If you reconnected the vent to the tank, did you check the end of the vent line to make sure it isn't blocked? Have you made certain that the vent thru-hull isn't clogged up?

Have you made any effort to find out if you're the only one who can't seem to make this particular pumpout work? Have you tried using a different pumpout at another marina?

Bill Roosa · Dec 27, 2010

something simple to try

Most pump out hoses are stored coiled. That means you have to lift the crap even higher to get it "over the hump." Try taking all the coils off the storage rack and laying them flat on the dock. For my setup this effectively haves the amount of lift I need to achieve effective suckage.
Simple, effective, easy to remember!

Bill Roosa · Dec 27, 2010

soft hoses

The hose from the pump out port to the tank could have a soft spot that is collapsing when you apply vacuum. You would have to feel around the whole length of hose to confirm.

How much vacuum does it take

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