V A C U. FLUSH

[tonyiiiafl]

A couple years ago, my forward vacu flush was running a lot. I replaced the bellows, pressure switch, and duck bills. Seems there were only 2 duck bills total, I added the adaptor to ensure there were the required 4, 2 on each side. Out of nowhere, the thing started going off every 3 or 4 minutes. MAy I add, we use the forward head for “liquids” not solids. The stern one works flawlessly and always has.

Where would you start<?? check the bellows? replace duck bills again? That pressure switch was pretty expensive if I may add. New O ring etc.

Again, asking for thoughts.

Thanks!

[tonyiiiafl]

I am going to start by inspecting bellows and duck bills. I will replace duckbills when apart. I do not think bellows as there is plenty os vacuum when it flushes. I hope not the pre$$ure switch again! May remove and inspect too.

[Midnightsun]

Oddly enough I had a similar issue this spring even though I rebuilt the forward head a few years back. My issue was the motor would not stop. The unit did build up pressure as it would flush no problem. Water would remain in the bowl so no leaks in that area. I simply shut her down with the sleep button and figured I would tackle it on another day/week/month as this head is only used when there are guests on board. Our daughter was on board last week and I explained she needed to turn off the sleep switch and let it run for 30 seconds or so, flush and then return the sleep switch to the on position. A couple of days later I checked and she had forgotten the switch in the on position however the motor was not running. Bottom line is it fixed itself. Can only imagine there was some small particle/s stuck in the duck bills which prevented the bellows from reaching full vacuum which dislodged after some flushing and corrected the issue. All is functioning normally now.

I did play with the pressure switch when it was not shutting down, was able to manually open the switch with a screwdriver to shut her down but when flushed once more she still would not shut down. That pressure switch is really a major ripoff at the price it is sold for, one of those things where you really have no choice if it goes bad and they soak you or maybe I should say hold you under water until you drown when you buy one.

There is an adjustment on the spring that can change the shut on/off setting however it does not make much of a difference IMHO. Here is a picture which is self explanatory. https://www.amazon.com/Dometic-385318032-Vacuum-Tank-Switch/dp/B002IV6WV0

[Viper]

Interesting point about only having 2 duckbills. What model pump do you have, duckbills are on the sides of the pump correct, none on the bottom? Is the pump black or white?

Don't touch the switch, that should be your very last resort when you've confirmed everything else has been ruled out. To help with diagnosing leaks, you should get the Sealand vacuum test gauge. You can get it in a kit that includes, bowl seals, duckbills, and a water valve; P/N: 385310228, or you can get just the gauge; P/N: 318530002. It's a good tool to have on board if you plan on doing your own work.

When you install new duckbills, you should lubricate their bases before installing them. If you don't, they tend to twist and distort when you tighten the fitting. This causes the duckbill to open up a bit leading to vacuum loss. Lubricating allows them to spin with the fitting without distorting them. Don't overtighten the fittings.

[Midnightsun]

When you install new duckbills, you should lubricate their bases before installing them. If you don't, they tend to twist and distort when you tighten the fitting. This causes the duckbill to open up a bit leading to vacuum loss.

Awesome tip, thanks.

[bud37]

Source of the post Bottom line is it fixed itself. Can only imagine there was some small particle/s stuck in the duck bills which prevented the bellows from reaching full vacuum which dislodged after some flushing and corrected the issue. All is functioning normally now.

Interesting to hear that story as it reminds me......years back a slip neighbour got some crystalline tablets that you let dissolve in the bowl and they were supposed to clean the system and de smell the tank .. Tried them.... Well what actually happened was the particles stuck the duckbills open slightly and we had to do what Hans was explaining. After a while with flushes and NO MORE tablets they were fine......lesson learned, it sometime takes very little to short circuit things.

I would imagine heat, dried out and little use may distort the same way.

[Viper]

Source of the post

When you install new duckbills, you should lubricate their bases before installing them. If you don't, they tend to twist and distort when you tighten the fitting. This causes the duckbill to open up a bit leading to vacuum loss.

Awesome tip, thanks.

What it ultimately leads to if you don't lubricate is that you end up throwing all kinds of money at the problem because the duckbills (which are now twisted) haven't solved the problem, so the thinking is that it can't be the duckbills, they're brand new, I just replaced them. So you start suspecting bellows, vacuum switch, etc. $$

Get the gauge I mentioned above, it comes with useful instructions and specs that one should know about when diagnosing the system otherwise you could be chasing something that really isn't a failure at all but is within normal parameters, and can prevent you from throwing unnecessary parts at the problem due to guesswork. It'll tell you if you have a leak, at what rate, and whether your pump and switch are functioning properly.

BTW, I don't recommend using any holding tank treatment that is in a solid form. The only solid one I will use is Noflex Digestor but I let it dissolve in the bowl first. You can see it fizzing, then I flush. I don't like pucks, pouches, etc. Any other product I use is in liquid form only. For me, that goes for any toilet that has duckbills.

[tonyiiiafl]

My pump is black. The pump had only 1 on each side. I had to get the duck bill adaptors to add the second WHy I can’t say as i bought the boat used. Like I said, plenty of vacuum. I ordered the gauge, yes a great tool to have around.

[Viper]

Use the gauge per instructions as it will help narrow down the source of the fault. Considering what you've already replaced, you've either sprung a leak somewhere or it's the typical cause of debris in the duckbills keeping them open. Other possibilities are a clogged line either before or after the vacuum generator, a full tank, blocked vent, bad shaft seal and or leaking cartridge at the toilet, leak at pressure switch, etc. If your toilet bowl isn't holding water, it's a bad bowl seal.

Using only one duckbill on each side of the pump is typical of a pump that's being used for discharge applications, not maintaining a vacuum. Interesting that it's the way yours was set up. Likely a previous owner modified for some reason, it wouldn't have been the way the pump came from Sealand unless something happened on the assembly line.

BTW, I like using dish soap to lubricate the duckbills. You only need a small amount on each one. Don't use typical machinery greases. I've also used the lubricant you can get for impeller installation. They come in tiny one use tubes and I always have several in my toolbox at all times, I put that sh#t on everything!

[tonyiiiafl]

I got into the duckbills this AM. the input. side I had installed wrong, one facing it, one facing out. , one in one direction one in the other. The discharge both same outward direction. After changing these a marked change in operation, but still comes on for a brief time every 4 or 5 minutes,. I looked at the situation and saw the input side has hose that is not fully seated on the nipple, so I am thinking that it may not be sealing. I am going to replace that hose with the more pliable one I used for the entire black water system. I was able to snug up the pressure switch a bit, may pull that out while waiting for vacuum guage. Water holds fine in the bowl. I mean, I could live with it like this for the season, as we can switch on and off, but i am one who believes it should work as intended. The saga goes on.