Friday, November 30, 2012

It's Always the Joker

rev 2-5-2013

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)
The Raritan PH II will provide about 25% more presure through the use of a lever arm. On the other hand, the Jabsco joker valve opens wider.


  1. I am very interested in what you find, as I have two jokers to replace - right now! - according to Jane.

    Besides the usual, only vinegar and salad oil go in our heads. Any recommendations?


  2. If it's a Jabsco head, Skip the oil and lube with synthetic grease by opening it up. That is what the manual states, because the salad oil is a no-no for neoprene joker valves. Other brands can better tolerate the oil.

    If you must use oil, only soy bean or canola oil; olive oil is not good and corn oil is worse.

    But oil in general can also be an odor problem; because it floats on the surface it prevents air transfer into the holding tank and promotes anaerobic conditions, leading to stink. Sewer authorities restrict oil and grease (including vegetable oil) to about 100 ppm because of sewer clogging and treatment problems.


    So much misinformation out there, often from authoritative sources but in conflict with the manual.

  3. How do you winterize your head, Drew? Do you use the pg stuff?

    Rick - s/v Cay of Sea - just down the creek from you.

  4. Mid-Chesipeake-specific comment:

    Yes, I do winterize the head. Though it seldom gets that cold, I have frozen water bottles a few times and did break one pipe fitting the first year I had the boat. The prior own said "just blow it out," but he lived in Deltaville. I later found additional signs of repairs; he'd busted a few things and just didn't want to talk about it. I've had no issues since.

    This post ( describes the specifics. I also flush with weak EG through the winter, to keep the tank and bowl freeze-proof. We just keep a jug with 20% EG in the head.

    I have always used EG on the blackwater system and never suffered any material compatibility issues. Joker valves last a few years.

    Yes, I use PG on the potable system. This rather long post covers antifreeze and why EG is no more toxic in the Bay than PG.

  5. Nice article... Although you have been misinformed about your "nylon potable water strainer bowl". That is definitely not nylon, as nylon is never clear and nylon (with few exceptions to rare solvents) never "crazes". The material of that bowl I could guess at (I'm a plastics guy), although it wouldn't matter at this point. But that strainer bowl is NOT nylon.

  6. ^^ So right you are. The based is nylon and the bowl is probably styrene-acrylonitrile (SAN), though I could not get a straight answer from the maker.

    What caused the stress cracking? While there are many agents that could be responsible, in combination with mechanical stress, we may never know. What does seem clear is that the failures correlate with polypropylene glycol winterizing agents.

    Nylon bases are also susceptible to cracking when winterized with PG. EG does not seem to have this effect.