Dosing fertilisers in proportion to flow
A proportional doser injects a stock solution into the irrigation network in proportion to the water flow passing through it: concentration stays constant however many drippers are open. That is the fundamental difference from a fixed-output pump, which drifts as soon as the irrigation regime changes.
What a water-driven doser does — and does not do
A water-driven volumetric doser is powered by the water flow itself: it needs no electrical supply. On the other hand it carries no probe, no electronics and no feedback. It applies a dilution ratio; it does not correct pH or EC drift, and it does not compensate for a badly prepared stock solution. Closed-loop pH/EC regulation is a distinct function, carried by an in-line electrode and a dedicated injection loop: the two devices complement each other, they do not replace each other. Confusing them leads to buying a device for a function it does not perform.
Sizing: flow before dosing rate
- Permissible water flow range (m³/h) and the pressure drop introduced: this is the first selection criterion, before the injection rate. An undersized doser throttles the network; an oversized one will not start at low flows.
- Working pressure range (bar), minimum operating pressure and pressure available at the far end of the network.
- Dosing rate, expressed as a percentage or a dilution ratio (1:x), fixed or adjustable, and the repeatability of that rate over time.
- Number of channels: stock solutions are kept separate (tank A, tank B) to avoid precipitation between calcium, sulphates and phosphates in concentrated form. A multi-channel frame handles this; a single channel requires a compatible preparation.
- Chemical compatibility of the seals with the products injected: acids, peroxide, chlorine, concentrated solutions. The seal kit is chosen with the product, not after it.
Network protection and filtration: the two non-negotiable points
Injecting fertilisers into a network connected to a potable supply requires a correctly sized backflow prevention device — a break assembly and check valves upstream of the injection point. This is not a comfort option: it is the condition of connection.
Upstream, filtration by screen or disc, with mesh size expressed in µm, governs the life of the doser as well as that of the drippers: clogging is the leading cause of breakage and of dosing drift. An outlet check — EC and pH of the diluted solution, volumes recorded — remains the only way to verify that the rate applied matches the rate expected.
Maintenance: a consumable, not a sealed appliance
The seals of a proportional doser are consumables, replaced at an interval linked to the product injected and the volume treated. No model is “compatible with all fertilisers”. Ordering the spares kit at the same time as the unit avoids a stoppage in the middle of the irrigation season.
Where to go next
GrowLED lists Dosatron proportional dosers and studies multi-channel injection frames against a specification; the flow and pressure of the chosen model are checked on the manufacturer's data sheet. Pressurising the network is a matter for booster pumps. For non-professional use, our watering and irrigation equipment covers small networks, and manual dosing by syringe remains suitable for small volumes. Back to grow room automation.
