If you have been reading this blog, you already know that marine heads are different from household toilets in several meaningful ways, even if you live ashore. If not, know this: the marine head must pump the bowl contents up with a minimal amount of water, rather than flushing the contents down with prodigious quantities of water.
Because it is a pump, the marine head has moving parts, and more importantly, it has check valves - devices that are supposed to only allow fluid flow in one direction. The Joker Valve is one such check valve - all the bowl contents must pass thru the joker valve on their way to the holding tank.
Howz'at work, you might ask? Well, if I squeeze the valve a little, you can see how the lips open - you are looking here at the discharge end of the valve. Yup, everything that goes in the bowl has to go thru there.
Now, joker valves do not last forever. To work properly, after the lips have been forced open by passing fluid or solids, they need to spring back closed to prevent backflow. And over time, the lips lose the ability to do this. And so the valve must be changed out. The ones in our heads have been in there for 2 years, and their time is up - after use, the bowls slowly fill up with the stuff that has most recently been pumped out. Yeah, not pleasant. Today I will replace them both.
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Jabsco, Raritan, Groco
To the left are three different joker valves, showing two different designs and three different materials of construction. Our heads were made by Jabsco and so we already have a data point for the upper valve - it was what came with the heads, and lasted for about two years.
Today, I installed the Raritan valve in the aft head and the Groco valve in the forward head. We'll see how they do over the next couple of years or so.
And here's what a joker valve looks like when coming out of service - it's easy to see why this one doesn't work any more...