Strange Head Behavior

[Wanu]

I have a Jabsco and a Raritan, both manual. Recent the Jabsco was unused for a few days and when I returned the pump would fight me in the push down of the handle when in flush position. Drain was not the issue as in dry mode it pumped freely and would pump out added water from the shower nozzle just fine. Then, after buying a new pump and planning to replace it and rebuild the old one it freed up and now works fine....the joke was it saw the new one on the counter.
NOW the Raritan is doing the same thing. Was not unused at all just started up after last pump out. Only when pushing down in flush mode it pushes back. In dry mode it too pumps fine and adding water from the shower it pumps it our freely.
Anyone who understands the operation of these have a suggestion on what the cause is and why intermittent like this? Never happened before...
Thank you!

[peghall]

If it's happening with both toilets, I'm guessing that the problem is a blocked holding tank vent.

All tank vents have two main functions: to provide an escape for air displaced by incoming contents and provide a source of air to replace contents as they're pulled out. When air displaced by incoming waste cannot escape out the vent the tank becomes pressurized, creating increasing back pressure that prevents the toilet from flushing.

Without a source of air to replace contents as they're being sucked out of the tank, the pump will pull a vacuum that'll prevent it from pulling out more than a gallon or two. A particularly strong pumpout can even implode a tank.

So do NOT use either toilet again or try to pump out or dump the tank until you've cleared the vent.

The two most common locations for a vent blockage are the vent thru-hull and the other end of the vent line--that end of the hose and the vent fitting on the tank. Start by cleaning out the thru-hull...use a screwdriver blade, ice pick--whatever works. If that doesn't result in a spew out the vent, you'll need to relieve the pressure before removing the vent line from the tank to clean them out...so open the deck pumpout fitting VERY CAREFULLY with a hose at the ready. Be sure you're UPwind of it! Scrape out that end of the vent line and the vent fitting on the tank...reconnect the vent line.

If there's a filter in the vent line, remove it...once a filter gets wet--which can happen when a tank is overfilled or even due to heeling--the charcoal swells and blocks the vent...one of the reasons why vent filters aren't recommended for use on most sailboats.


I'll be glad to answer any questions.

--Peggie

[leecea]

So they pump fine in dry mode (and can clear water you've added from the shower) but they won't pump when trying to draw raw water in flush mode?

Is the seacock open? Is the strainer clogged (if you have one)? Is something blocking the thruhull?

[Wanu]

Like I said, they both had the same issue but the Jabsco was not going to a tank and the Raritan is. Not the vent as it pumps to the tank fine with added water and in dry mode. Only in flush mode. First one cleared itself up but now the other is fighting me. No strainer on these lines and valves have always been open....

[sck5]

Some creature tried to find a home in your through hull and/or the hose? It happened to me. And I didnt have a strainer

[Wanu]

Strangest thing - now this one cleared up....!!

I guess nobody knows enough about how they work to troubleshoot this behavior. Was hoping someone would know. I wanted to learn about it.
Oh well, working again.

[HopCar]

It sounds like an intake problem not a discharge problem. Since they work fine in the dry flush mode it sounds like water is not being allowed in on top of the piston. In dry flush mode a valve is opened that allows the piston to draw air in from the bowl rim. This prevents a vacuum from drawing water in on top of the piston. It sounds to me that either the intake valve is stuck closed or the intake line is blocked somewhere. What you feel as you push the piston down is a vacuum on top of the piston.