All the water goes through there. It actually has a cover on it, but I've taken it off so you can see inside.
So, there's a large, plastic bulb there, held on by a silver-coloured metal ring. Inside the bulb are spherical sisyphus crystals (that's the trade name for them), which do something along the lines of Perform Miracles. Every year or so, I have to take them out and replace them with a new batch. The process begins with a reminder after 10 months, which I ignore because if I heeded it then I'd put the crystals in two months too early and after five years would have used six years' worth of crystals.
The problem with this set-up is not the timing: it's doing the actual replacement. You start by turning off the mains, then loosening that red stopper. This releases the mains pressure, meaning you have a fighting chance of getting the metal collar off. This allows you to take out the bulb and empty the old crystals into the bowl you remembered to put in place earlier. You then put the bulb back, tighten up the metal collar, then refill the bulb through the hole that the red stopper stops up. This done, you replace the red stopper, turn on the mains, and begin your despair.
Well, actually your despair started at the beginning because of what happened last time.
As the water is under mains pressure, the seals have to be very tight. That's very tight. You have to turn the collar as far as humanly possible, then when water still drips out of it begin to use inhuman means. It's such a big collar that I don't have a tool that fits it. I've tried using a leather belt, a hammer and cold chisel, a pair of thick, leather gloves — they don't work. What does work is if I take my bench vice and tighten that up on it: this has enough grip that I can then rotate it that extra sixth of a circumference it needs to be turned in order to stop dripping. Having tightened up the collar, I then put in the red stopper and hope for the best. This has to be tight too, of course, but at least it comes with a spanner-like tightening tool.
Of course, as the collar is so tight, this presents a problem the following year when I need to get it off. The key is to undo the red stopper first, to take the pressure off the collar. Unfortunately, the red stopper is also under pressure and is extrememly reluctant to move. It's so reluctant, in fact, that the integrity of the stopper (which is made of plastic) is less strong than the force required to rotate it. Two of the six corners on the top of the stopper have come off in previous years. If the whole thing were to break, I wouldn't be able to turn the mains back on as there would be nothing to stop it from gushing out.
Even with the stopper out, releasing the metal collar is no easy job. It tends to be marginally easier than tightening it, but that's not saying much.
It took me three attempts over the course of several hours yesterday to get the collar on tight enough to stop it dripping. This is not a job I look forward to at all. I'm thinking I may look to buy a special tool for it next time (I know they exist, but our plumber doesn't have one).
Oh, and the reason I don't want it dripping even occasionally is that the electrician who wired up our heating system a couple of years ago decided to put the earth (ground) connection on the water main directly beneath this water softener, so if it's wet and we do get a short circuit, it might not turn out well....