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How to make a spund valve without spunding any money

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  • How to make a spund valve without spunding any money

    As we are about to leave the holiday season, and it seems that some folks are interested in the results of tinkering. I thought I’d give one more report from Santa’s workshop, before the elves take a long deserved holiday.

    A spund valve is simply a low pressure relief or safety valve mounted on a closed fermenter (like a keg).

    Now, your first question might be: “Why would I need one of those, Doc?”

    The quite simple answer is: “You don’t”.

    Now I shall explain why you might “want” one.

    Most people start out brewing by doing a primary ferment, a secondary with a bubbler, and then mixing with a primer and bottleing. Sooner or later one decides that cleaning one keg takes a LOT less time than an equivalent amount of volume in bottles, and transfer the same procedure to kegging.

    Once kegging, and with a gas source on hand, most figure that if you just let it clear in the secondary, you can rack to a keg, skip the priming, and artificially carbonate.

    Now, if you are using one of these methods, and are perfectly happy with your results, you need read no further. You’ve already won!

    Most people who have been kegging awhile, realize that the whole secondary thing is a carry-over from botteling, and an entirely unnecessary step. Professional breweries go straight from the primary to fermenting under pressure, so why shouldn’t we? Simply racking straight from the primary to a keg, removes one entire process of handling the beer, eliminates a whole bunch of equipment (carboys, bubblers, lids), and a whole carload of cleaning, and reduces risk of unnecessary oxygen exposure and early beer staling.

    Now here is the real tricky part. Fermenting under pressure is NOT the same as fermenting at atmospheric pressure. I’ve heard this described as “slowing down the yeast metabolism”, sort of in the same manner as a colder temperature would. I’m not sure this is a correct description. If you really compare the two, I think you will find that the specific gravities alter at the same rate, so you’re not slowing down the carbohydrate metabolism significantly. I prefer to think of it as “specifically altering the metabolism of the yeast”. The point being, that a beer fermented under pressure will yield a different result than one which isn’t.

    I’ve tried to get my head around why this is so, and the best explanation I can come up with is that the pressure itself and/or the increasing carbonic acid concentration, selectively makes the yeast behave in a different manner, and create different taste products.

    O.K. Let’s say you’ve decided to abandon your secondary. The next question is when to rack from the primary. I am quite sure you can read and hear all manner of opinions on that subject, and admonitions to repeatedly make hydrometer measurements to get it “just right”.

    I am going to make a brazen statement here and just say “sooner rather than later”.

    So, you are past high kreuzen, the head is falling and you decide to rack to the keg. Perhaps it was a bit early and you ferment up enormous pressure. You’ve made a "gusher". Now you either have to drink about a third of a keg of foamy beer, or repeatedly vent through the pressure relief valve at the top of the keg to settle that puppy down. This is where the spund valve comes into play. If you had one of those on there it would have come to the correct pressure by itself.

    There are spund valves available for home brewers now, that are adapted to a Cornelius system, and you could simply buy one.

    Before you make that investment you may want to find out if this is a worthwhile thing to do.

    I am going to show you how to make one for free. You can then play with it and see if this is something you would like to pursue.

    You see, you’ve already got one on your keg…. The safety relief valve at the top. It is a spring loaded check valve. It is just made for gi-normous pressures to keep you from exploding your keg. We are going to change that.

    Simply take the lid off a keg, and unscrew the relief valve. The ring should be enough to unscrew it, if not, grab some pliers. Now, the only thing that’s holding this together is the pull ring at the top. Feed that off of there, and it comes apart. You have the cap, a spring, and a plunger. Remove that spring and keep it. If you decide to reverse this process all you have to do is put that back in. If you squeeze that spring you will notice that it has quite a bit of tension, and is nearly as long as the shaft of the plunger. Now you need to find a spring that is about the same diameter, but quite a bit weaker, and longer (see pic1. A bunch of springs), and pic 2, the original spring and the one I have chosen (there is also a tube “spacer” as I played with several variants).

    Now if your kegs are over 40 years old (like mine) or you bought them used and don’t really know their age, you may want to inspect the rubber gasket at the bottom of the plunger. I believe there are some modern variants with o-rings there but I’ve never seen one in reality. They all just have some round rubber seal glued into the plunger.

    If your keg is fairly new, skip this part. If older, you may note that this rubber, or butan, or whatever material it was made of stales with age, and while it may have worked at high spring tension, you want a nice spongy seal for this one. If you think it needs replacing, just poke the old one out (they come out quite easily). To replace it you can take some rubber sheeting and a punch, or just find an o-ring of that diameter (it turns out that the lid o-rings are often just right!). If you are using an o-ring simply make two slices with a razor sharp blade. Make it with a slicing motion. If you push down while cutting you will get two concave surfaces. Pic.3 shows a bit getting sliced, and 4, the chunk you got out.

    “Super glues” are cyanoacrylates. Quality ones are chemically altered according to what material they were intended for. If you are doing a lot of tinkering with these kinds of thing you might want to invest in something like Loctite 480. It’s worth it only if you do a lot of this stuff. It IS expensive. One tube will last for years, in my experience, but if you have no further use for this just use “grocery store super glue”.
    If you pushed a bit hard while slicing try and trim one side of your new gasket as flat as possible (this is not terribly critical… I’ve never had one of these fail). Scrape clean the inside of the plunger head and give a quick wipe with the solvent of your choice (acetone, alcohol, whatever). When dry put a drop of glue in, put the rubber bit on, and put it in a vice to let it dry with a well seated chunk of rubber (pic. 5).

    The seat on the inside of the lid of all the cornelius kegs I’ve poked my nose into is slightly concave. When doing this to replace a faulty high pressure safety valve, I’ve just spun this in my fingers on a belt sander to approximate that convex shape needed. They always work just fine. Here I want a more precise seal, so I bevel the rubber.

    This is done very easily by simply putting the plunger shaft in a drill, turning it on, and then place it at any angle of your choosing to a grinder, a belt sander, or just a well anchored piece of sand paper. Pic 6 shows this, and pic. 7 the resultant beveled gasket.

    If you didn’t find any other source of material for your gasket, you might pull the eraser off a pencil. Check it first. If the diameter is too large, now that you’ve mastered the drill and the grinder trick, put the pencil in your drill and come in with the eraser at 90 degrees to your grinding surface to make it any size you want before removing it. If you have a 6 sided pencil, it just looks like they were made for the chuck of a drill, don’t ya think? While your standing there, mount the pencil the other way round, pick your angle and make the sharpest pencil you’ve ever held!

    Being careful not to poke your eye with your newly sharpened pencil, put the whole thing back together but with the new spring you’ve chosen rather than the original. If your keg is fairly new, you don’t have to have done any of the above but you will miss out on the really sharp pencil… just change the spring. Fill your corny with water (so you don’t waste a lot of gas) put the lid on with your new spund valve, hook up the gas and regulater, and see what you got!

    Chances are it will be too high. Then just clip off one ring of your spring, and test it again. When you get between 2 and 3 bar, you might want to start going half a ring at a time. Stop when you are happy.

    I’ve got mine set at 0.8 bar which I think is OK.. So I can see that this is a spunding keg, I have a bit of solder twisted around the handle with some o-rings threaded on it the size of the shaft of the plunger. If I opt for more carbonation, I just add o-rings above the spring as needed.

    I do like playing with fermentations. Last year I did some ‘spurments with varying oxygenation during primary. I did it with a live Heurlimann strain and Saflager 34/70 (which should be the Weienstephan strain). I had three different exposures for each strain. I invited 3 brewers over to blind taste what was now 6 different beers. The interesting thing was that each brewer could distinguish between the strains, and each consistently preferred the same one. MORE interestingly, they were not the same choice! If you preferred the Huerlimann strain you preferred it at every ferment. If 34/70 tickled your fancy, you always preferred that one in each blind tasting regardless of fermenting technique.

    The “sense morale” of that little tale? Nobody can tell you what you should like… we are all different.

    You might want to try spunding your lagering.
    You may even want to try fermenting your primary under pressure.

    You may produce something that you like even better…
    or you may not.
    Pics. 1 & 2: Rummage, or salvage springs to find a likely fit. Pics. 3 & 4: Slice, don't press, if an o-ring is your choice of gasket raw material. Pic. 5: Putting pressure on the newly glued gasket will help it seat well.

  • #2
    Thanks for sharing this, Doc. Do you have dimensions for your approx 0.8 bar spring, as a starting point?


    • #3
      Gosh. What I actually used was in the picture. I would just suggest "skinny" and "long"?, I did not mention that making a beveled fitting on the gasket will more likely present a higher relief pressure than a flat one, which was my intention, so I could fart around with cheesy springs. My base insecurity and lack of practical knowledge before starting is why I made the tube "spacer" just in case.... which I never used.

      It turned out really, really easy at first try. If your only spring you can get ahold of is from a ball-point pen, then you might have a bit of ingenuity presented in front of you (very weak, small diameter, and "stick-slip" friction properties to be accounted for)

      Pretty sure you can get it together.

      Absolutely sure that if you want help...well that's what I do.