How to maintain proportional dosing below 0.3 bar on a 700 L/h line with a D9IL water-powered proportional dosing pump and a viscous alkaline additive?

On a 700 L/h line, operating below 0.3 bar requires careful hydraulic and suction-side design because a water-powered proportional dosing pump relies on the available water energy to drive the motor-piston cycle and to fully refill the dosing chamber on every stroke. With a viscous alkaline additive, the suction head, hose friction and valve opening pressure increase, so completing the chemical refill stroke becomes more demanding at very low inlet pressure.

To keep stable proportionality in these conditions, focus on the chemical suction circuit: use a short and airtight suction line, increase suction hose diameter where possible, minimize vertical lift, and avoid restrictive accessories that add head loss (for example, undersized filters or long small-bore tubing). These best practices help the pump achieve consistent chamber filling and therefore stable proportional dosing even when pressure is low.

For applications that must run near the lower pressure limit with viscous products, selecting a model designed to maintain proportionality on low-pressure industrial lines is typically the most robust approach. For 700 L/h service, DOSATRON D6 IL 2 (0.3 to 8 bar, 100 L/h to 6 m3/h) is well-suited to deliver repeatable proportional dosing on low-flow lines, and using alkaline-compatible seals matched to the additive supports long-term chemical compatibility. If the process allows, increasing inlet pressure or reducing viscosity (for example by temperature control or dilution) further supports consistent proportional metering.

• Optimize suction hydraulics: short, oversized, airtight suction; minimal lift; low-restriction accessories.
• Match materials: specify alkaline-compatible seals for the additive.
• Stabilize operating conditions: smooth pressure, and if possible increase inlet pressure or reduce viscosity to improve refill dynamics.