How automatic hygiene flushing works: intervals, duration, smart mode, delay

What a hygiene flush is

Nothing exotic happens during a hygiene flush. A timer reaches zero, the controller opens the solenoid valve at the outlet, water runs for a set period, the valve closes, and the timer starts again.

The settings are what make it useful. One controller can run a washroom tap on a 72-hour regime and a shower in a facility that stands empty for months, using the same hardware and different configuration. The fixture, valve, power arrangement, and pipework will of course differ between those installations.

The four settings

Four values describe most regimes in use. Each is a configuration decision rather than a hardware one.

Cycle: how often

In practice, 24, 48, and 72 hours are the intervals seen most often in the field, and weekly appears on emergency fixtures where a maintenance activation is scheduled alongside the required test. There is no single accepted frequency across buildings and jurisdictions, so the interval should come from the site’s water management programme and the guidance that applies to it. Setting the cycle to zero switches the hygiene flush off, which matters for products shipping into markets where the function is not wanted.

Duration: how long

This is where regimes are most often set badly, because the number tends to be guessed. It can be derived instead.

A duration below that will exchange or dilute part of the standing volume, but it will not achieve the full replacement the regime is designed for. Beyond the calculated exchange, the water age benefit falls away quickly, so a much longer flush mainly adds water consumption, and energy where the water is heated or tempered. Extended running is not useless in every case, since a longer flush can carry loose sediment and particulates out of the branch, but that is a different objective and should be chosen deliberately rather than arrived at by setting a generous number.

Once volume and flow are established, the controller repeats the timed opening, and continuous flow measurement is not needed for that to work. What it assumes is that actual flow stays reasonably close to the commissioned value, so a change in supply pressure, a partially closed isolation valve, or a fouled aerator is a reason to re-check the setting rather than to assume it still holds.

Type: standard or smart

A standard cycle runs on its interval regardless of what users do. A smart cycle resets the cycle timer on a user operation, so the interval runs from the last use rather than from the last flush.

Standard cycle vs smart cycle

Smart mode avoids cycles at outlets that were used anyway, which reduces water consumption. How much it saves depends on when activations fall relative to the cycle rather than on how many there are: a single use late in a cycle can defer a flush by the full interval, while a cluster of uses in one morning changes little.

There is an assumption inside that behaviour worth making explicit.

The reset treats any user operation as equivalent to a flush, and hydraulically that only holds if the use actually exchanged the standing volume.

A short activation on a long branch postpones the flush while leaving most of the standing water in place, and repeated short uses can keep postponing it indefinitely, so shortening the interval does not bound the worst case. Compare a typical use against the exchange time calculated for that outlet. Where normal use runs at least as long, smart mode behaves as intended. Where it is routinely shorter, use a standard cycle, which makes no assumption about what users did. Control logic that only resets the timer after a qualifying duration or volume, or that enforces a maximum interval which user activity cannot defer, would address this directly, but treat that as a design option to specify rather than as a given.

Standard mode is not the lesser option. Where the site’s programme specifies a fixed interval that must run irrespective of use, or where every outlet must be identically configured and easy to describe, a standard cycle is the simpler thing to specify and document.

Start delay: when the schedule begins

The delay holds the first cycle back for a set period after power is connected, and it runs once.

Its purpose is practical. Commissioning happens during the working day, so without an offset the first flush and those that follow tend to land in occupied hours. Customers report that unexpected daytime activations get read as a fault and generate service calls. Setting a 12-hour delay at a 2pm commissioning moves the first cycle to 2am. Reconnecting the power supply restarts the delay timer, so the offset can be re-established after maintenance.

What the delay sets is the starting point of the schedule, not a permanent time of day. The clock time only holds if the cycle is a whole number of days and the unit stays powered, and in smart mode later use moves the next flush relative to the last activation.

Flushing outlets together or apart

A fifth decision sits above the four settings, and it belongs to the installation rather than to the device: whether outlets run their cycles independently or together.

Offsetting start delays across a building spreads the demand and stops a whole riser drawing at the same minute. It is set at commissioning like any other parameter, and it applies where cycles would otherwise coincide without a reason for them to.

Grouping applies in a narrower case. Exchanging a branch is a matter of volume and duration, and a modest flow achieves it given long enough. Where the applicable regime or the hydraulic design calls for a target flow velocity in shared pipework, or where the flow path cannot otherwise be demonstrated, a single outlet may not draw enough on its own, and opening several at once becomes the way to reach it. Establish that the condition applies before designing around it.

It is not a free technique. Simultaneous opening only works where the supply can deliver the combined demand. In an installation that is undersized for it, partly scaled, or otherwise degraded, the result can be a pressure drop, mixing valves pushed out of balance, disturbed deposits and discoloured water. Which approach applies is a hydraulic question about that specific installation, settled before the cycles are configured rather than after.

The timers around the flush

The flush settings work alongside the timers that govern normal use.

Security time limits one class of fault rather than guaranteeing the outlet is dry. What it cannot do is stop water driven by something outside the timing logic, such as a mechanically stuck valve or a failed output stage.

Delay in filters brief unintended inputs, and it is the setting to raise where a unit is installed somewhere subject to unusual vibration.

Operating modes

How the outlet responds to a user press is a separate choice from the flush regime, and three modes cover most fixtures.

The flush function is separate from all three: it has its own duration and its own trigger, and it does not change how the outlet responds to a user. The one interaction is deliberate, in smart mode, where a user activation resets the flush timer.

Valves and power

Valve type shapes the power profile of the installation.

A controller that can drive both types is an architecture choice rather than a power one. It lets the same electronics serve a mains-powered product and a battery-powered one without a hardware change, which matters more to a manufacturer with a range than to a single installation.

Standby current is the other half of the budget. A flush controller spends nearly all its life waiting, so idle draw is usually the largest single contributor to battery life in a low-duty installation. It is not the only one. Active current, pulse energy per activation, activation frequency, battery capacity and chemistry, temperature, and self-discharge all belong in the same calculation.

Worked settings

Three installations, and the settings that follow from them.

A washroom tap in an office building. Programmed mode with a bounded flow time. Smart flush type, 72-hour cycle, duration derived from the branch. In a busy office the flush rarely runs; across a holiday period it runs on schedule with nobody walking the building.

A shower in a seasonal facility. Programmed on and off for users. Smart mode suits most of these sites, since normal use during the season is exactly what should defer a flush, and during closed months the cycle runs at its interval either way. Choose standard mode where the site’s programme specifies a fixed interval that must run regardless of use. Cycle in the 24 to 72-hour range, duration long enough for the run to the shower head, delay set so cycles begin overnight.

An emergency shower or eyewash. Here the scheduled activation is a maintenance function and must be kept separate from emergency operation. Equipment designed to ANSI/ISEA Z358.1 is intended to deliver flushing fluid for a full 15 minutes, with a valve that stays open until it is deliberately closed, so the control arrangement must never impose a timed cut-off on the emergency path. A weekly automated activation clears the standing water in the supply and exercises the valve, which is useful in its own right. It does not by itself confirm that flushing fluid reached the head, that the pattern was correct, or that the fixture is otherwise serviceable; that still requires observation or suitable feedback. Where no mains supply reaches the fixture, the arrangement runs on battery with a latching valve. Safety showers and eyewash: automating the weekly activation covers this application in full.

Where this is implemented