Head system vacuum loss

Mightychan

Mightychan

Member
Oct 8, 2016
157
Panama City FL
Boat Info
2005 DA 420, AB Dink
Engines
Cummins 6CTA
With my head on and not being used, I hear the vacuum pump kick on every 5 minutes or so. I assume that I have a slow leak somewhere. Is this just normal or is it something that I need to repair? And if I need to repair, how do find a vacuum leak? Pressure leaks are easy, just use soapy water in a spray bottle, but I have never had to chase a vacuum leak. Thanks!
 
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I had an issue with my peddle leaking. Got this on ebay and fixed the problem
Screenshot_20200322-191421_eBay.jpg
 
I will throw in a hopefully rare issue, but it was very difficult to diagnose until the end.
If you have (and you may not) a molded neck for the vacuum generator inlet (the hose from the toilet), I finally discovered that the neck was collapsing when under vacuum, causing the pump to cycle every couple of minutes.
My final fix for this will be to get the insert that is used on modern vacuum tanks, cut off the nipple, and hope for the best. Not even sure I can get the "old style" molded nipple tank anymore. BTW, Dometic threw me a blind ear when I asked about this. I would have at least appreciated a "well, it's twenty years old, so we aren't going to do anything about it, but yep, that was a design flaw."
 
Your other question was is it normal for the pump to cycle every 5 minutes. Answer is No. It should only cycle when flushed.

I've rebuild both of mine over the last 2 years and I can leave for a week and the vacuum generator will not cycle.
 
So both heads are holding water, so I suspect the duckbill valves. Where are they located? From what I see on YouTube, it appears that they are just upstream of the holding tank? How many are there in a 2 head system? Anyone know which size I would need on a 2005 420 Sundancer? Any tricks (other than flushing some soapy water before starting work) that I need to know about? Thanks!
 
We have 2 heads and the aft has been perfect since we bought the boat 13 years ago. The forward/main head has been a little more problematic with cycling without use every 30-60 minutes. The duckbills had just been replaced before we bought the boat so I never went there, but I kept hearing about NoFlex Digester on CSR and 2.5 years ago I poured some down both heads as I was leaving the boat for the winter. In the spring when I turned the heads back on the forward has not cycled once unless it was flushed... Best $20 I have ever spent !
 
Mightychan said:
So both heads are holding water, so I suspect the duckbill valves. Where are they located? From what I see on YouTube, it appears that they are just upstream of the holding tank? How many are there in a 2 head system? Anyone know which size I would need on a 2005 420 Sundancer? Any tricks (other than flushing some soapy water before starting work) that I need to know about? Thanks!
Click to expand...
Just finished rebuilding mine yesterday. I'm assuming your setup is similar as mine. You may have 2 vacuum generators so verify which one is the offending unit. Its best to remove the whole pump assembly rather than try to take it apart at the location. Removing the inlet and outlet connections on both ends of the pump then unplugging the wiring harness should free everything up. I then removed the 2 bolts i could see that was holding the pump assembly to the base. There should be two similar bolts on the back side as well. I loosened those but left them in place so i could slide the pump assembly out. You may our may not have water in the pump assembly or the hoses so be ready. Once the pump is out you'll see its pretty straight forward to replace the duckbills. You should have the 1" 1/2 duckbills and you will need 4 of them. I ordered from these guys https://seacoastservices.com/ and i got them in the next day.
 
When / if you do your duck bill valves, be sure to have several pairs of rubber gloves. It is a messy job. When I did mine I took my entire pump assembly out and apart to clean it up like new. There will be crud stuck in the corners, etc. I actually, carefully, used a pressure washer on it. Just be careful of the switches. Not a horrible job, but a bit stinky.
 
Before you "Go Rambo" on the head system, knowing where you are and the previous owner of the boat, try this: There is sand everywhere in your boating environment and it takes only a few grains to keep the ball valve from seating in its gasket/seal. It is a teflon-neoprene combination, so fill the bowl with water and flush the leaky head, th en with t he ball open, wipe the seal with your index finger wet with freshwater. Finally, wipe the seal all th e way around with Vasoline on the tip of your finger and the chances are good you will solve the problem.

In case you do want to tear into the mechanism or replace the duckbill vaves, before you do, have the holding tanks pumped completely dry, or as dry as you can, then rinse them with freshwater so there is no waste to spill, because the duckbills are at the bottom of the vacuum pump and you will likely spill some of the remaining contents. A shop vac is your friend in this process..........
 
Thanks, Frank, I appreciate the advice, I will give that a try today.
You might be interested to know that we recently move the boat to Massalina Bayou. That tornado that touched down in last nights storm was only a couple hundred yards from the boat! We didn't sustain any real damage, but a couple of sailboats got their masts tangled up. The folks that were there for the storm said it got wild!
 
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