Every sailor with a manual head knows that the joker valve is the check valve at the bottom of the head, the one that everything has to pas through, the one that must be changed every 1-2 years, and... the place you will find most clogs.
This time of year folks start talking about winterizing and what they pour in or how they drain out to prevent ice damage. Sometime I hear of things I know are damaging the head, and I just cringe. A resent letter-to-the editor of Practical Sailor got me thinking; we haven't reviewed joker valves and the details.
Don't worry; this will only happen if you use Lysol in the bowl... which a few people do.
(Groco valve, but Lysol would do this to all of them. Also some head treatments contain formaldehyde (stinky blue stuff) and will do this if not well flushed. Better yet, ban these from your boat.)
This Jabsco valve (left) saw only waste and ethylene glycol and lasted 5 years. A valve in this condition actually leaks less than you would expect; although it is gaping, the lips are smooth and the back pressure holds them together. Occasional use of vinegar keeps the lime at bay. The head itself is 16 years old, though I replaced the pump assembly at 13 years (like new now).
First, all common joker valves are dimensionally interchangeable. Yup, Raritan, Jabsco, and Groco all use the same basic dimensions. But that isn't to say they all use the same valve or even that they are made of the same sort of rubber. They are not. The correlation, of course, is that their chemical vulnerabilities are different and that no single chemical compatibility list will cover all heads. Interesting, no? Some are not compatible with vegetable oil, while some are. Some are not even compatible with propylene glycol, though the PG manufacturers would tell you their product is safe for everything. The source of the above preliminary incompatibility data? Letters direct from the manufacturers.
Propylene glycol can be rough on other parts as well. While PVC and polyethylene do very well, my styrene-acrylonitrile (SAN) potable water strainer crazed in just 2 winters. Though they were good about replacing it, I just leave it off in the winter now.
So I have bottles lined up in my basement, full of joker valves and chemical concoctions. I'm measuring and testing compression and testing leak resistance. The goal? A better understanding of what should NOT go in the head. A recommendation for the best joker valve to go in your head perhaps.
What about the flexible impeller pumps for raw water and potable water? Some of the raw water pumps are nitrile and are immune to propylene glycol, but some are neoprene. After all, neoprene has a better flex life. There have been reports of PG damaging raw water impellers over the winter, ever since we bought into this well intentioned but wrong conventional wisdom that PG is better for the environment than EG.
A clue? Winterize all non-potable systems with EG.
Update 2-4-2013: Neoprene becomes about 2 times stiffer after 30 days of exposure to 25% PG and about 3 times stiffer with 5% swelling after 3 months exposure. Identical EG exposure causes no change. However, stiffness and size return to normal within 48 hours when soaked in fresh water. Any lasting harm? not certain.
Update 3-5-2013: Nitrile becomes very stiff when exposed to stale urine (ammonia) for extended periods, enough to cause leakage with in months. Sufficient flushing is the prevention.
Which manual head moves the most water? Some have said Raritan (the fan club), but that's just not so. I consulted all 3 factories directly to insure correct data. The volume per stroke are these:
- Groco HF: 5.9 ounces (calculated)
- Jabsco Twist-n-Lock: 5.9 ounces (calculated)
- Raritan PH II: 5.6 ounces (factory measured flow)