The decision the valve has to make
A softener must regenerate before the resin exhausts, but every regeneration costs salt, water and downtime. The control valve's job is timing that trade-off, and there are two philosophies.
Time-clock control regenerates on a schedule — every N days at a set hour, regardless of how much water actually passed. The valve is simpler and cheaper, and the logic is honest about its assumption: consumption is predictable.
Volumetric (metered) control counts the litres treated. The installer programmes the bed's capacity (resin volume, salt dose, feed hardness), the valve computes how many litres the bed can soften, and regeneration triggers when that volume — less a reserve — has passed. The assumption here is the opposite: consumption varies, so measure it.
What the difference costs and saves
A time-clock valve set for the busy week regenerates just as faithfully through the quiet one, spending salt and water on a half-loaded bed. Set it leaner and the busy week outruns the schedule, sending hardness through to the geyser. In practice installers set time-clocks conservatively — regenerate early, waste a little, stay safe — so the steady overhead is salt.
The volumetric valve simply does not have this dilemma: heavy use brings regeneration forward, light use pushes it back, and holidays cost nothing at all. At steady occupancy the salt saving over a conservative time-clock setting commonly runs 30 – 50%, which is why the metering premium typically repays itself within months to a year or two on any system with meaningful salt throughput — faster the harder the water and the more variable the usage.
Where each belongs
| Situation | Sensible control |
|---|---|
| Constant, predictable load (fixed process duty) | Time-clock is adequate |
| Household, guesthouse, office — variable occupancy | Volumetric |
| High hardness or high consumption (salt bill matters) | Volumetric |
| Water must never go hard (boiler feed, process) | Volumetric duplex — meter switches the standby vessel in |
| Tight budget, tolerant duty | Time-clock, set honestly and reviewed |
Two refinements worth knowing. Delayed volumetric regeneration (the common mode) triggers on volume but waits for the small hours, softening the reserve margin meanwhile — right for almost everyone. Immediate regeneration fires the moment capacity is reached — right for duplex systems and continuous processes. And every volumetric valve is only as good as its programming: a valve told the wrong hardness meters precisely and still regenerates at the wrong time. Re-check the setting whenever the feed source changes — a borehole switch-over can double the hardness behind an unchanged setting.
In the Runxin range this is the difference within series — e.g. the time-clock and volumetric variants of the same softener valve platform; the third digit of the new code convention encodes it (5 time-clock, 6 volumetric — see the Runxin code reference).
Rule of thumb: time-clock only where consumption genuinely is clockwork. Everywhere else, volumetric control converts unpredictability into salt savings — and on duplex systems it is not optional, it is the mechanism.