A short history of the dosing pump
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A short history of the dosing pump

The dosing pump concept was born in the 19th Century, when industry started to develop in Europe and concerns about healthcare and water quality were growing, writes Patrick Deniau of Dosparo Milton Roy. Since then technology changes have been pushed forward by the growing need for increased safety and environment protection.
The most commonly accepted definition of a dosing pump is a reciprocating pump that can have its capacity adjusted by varying its swept volume. Usually, this can be done while the pump is running, but some older designs can only accept a capacity change when the pump is stopped. The ability for the capacity to be changed while the pump is running provides the dosing pump with a very high degree of accuracy. As a result, pumps of this type are used to meter and inject additives and chemicals in almost all types of processes where accuracy is a critical factor.
Because it can serve many different processes, a dosing pump is able to accurately handle various fluids, including those that are corrosive, abrasive and radioactive, at even extreme pressure and temperature conditions.
plunger dosing pump head
Figure 1. Plunger liquid end.
Accurate delivery
In continuous processes for example, a constant rate of chemical injection is required and can be measured as the steady state accuracy of the pump, this qualifying the variation of the delivered flow around its mean value. Only reciprocating pump technology can provide steady state accuracies as low as 0.5%. Despite this degree of accuracy, the highly variable instantaneous flow delivered by a reciprocating pump (its pulsated flow), is a disadvantage. This is why dosing pump manufacturers offer pulsation dampeners as a typical ancillary device for their pumps. Pulsation dampening of +/-2% is currently obtained and this is below that which is usually expected from other hydraulic devices like flow meters.
In certain processes, a chemical injection function of process data may be required, such as in pH control. Here, two other types of accuracy have great importance, these being linearity and repeatability. Linearity translates how the flow delivered by a dosing pump is proportional to the flow adjustment order, through a 4-20mA signal for example. Repeatability gives an idea of the hysteresis inherent in all mechanical and hydraulic systems: each time the dosing pump is adjusted at a given setting point, it must deliver more or less the same amount of flow. The API standa