A metering pump that doses at ninety percent of its set point instead of one hundred percent does not seem like a large discrepancy until you calculate what that ten percent variance actually means to the chemistry it is supposed to maintain. In a cooling water system with several thousand cubic meters per hour of flow, a ten percent underdose of scale inhibitor over a sustained period means scale formation that would not otherwise occur. In a boiler feedwater system, a ten percent overdose of oxygen scavenger adds ongoing chemical cost and can affect feedwater pH outside the target band. In geothermal brine handling, where the fluid chemistry is already aggressive, inaccurate inhibitor dosing can mean accelerated corrosion of equipment that is expensive and operationally disruptive to repair.

Metering pump accuracy matters because the entire value of chemical treatment depends on it. A precisely specified treatment program that is imprecisely executed produces neither the cost nor the protection it was designed for.

What Accuracy Actually Means in a Metering Pump Specification

Pump accuracy is typically stated as a percentage of the set point or of full scale, and the difference between these two ways of expressing it matters considerably for how the pump performs at partial stroke settings. A pump rated at plus or minus two percent of set point maintains that accuracy across its full operating range. A pump rated at plus or minus two percent of full scale is only as accurate as that implies at or near maximum stroke, and the error as a percentage of actual dose grows significantly as stroke is reduced.

Most real industrial dosing applications do not run pumps at maximum stroke during normal operation. Pumps are typically set below maximum to retain upward adjustment margin as process conditions change. A pump whose accuracy specification looks acceptable at full scale but degrades significantly at the partial stroke settings actually used is less accurate in real operation than the specification suggests at first glance.

ProMinent’s metering pumps are specified for accuracy across their operating range, not just at nominal maximum, which is a meaningful distinction for applications that run pumps at partial capacity during extended normal operation.

Geothermal Service: Why Accuracy Is Even More Critical Here

Geothermal brine handling presents a specific combination of conditions that makes dosing accuracy more consequential than in general industrial water treatment. The brine carries dissolved minerals, chlorides, and dissolved gases that create corrosion and scaling potential well above typical process water, and the inhibitor chemistry managing that potential must be delivered within a relatively narrow concentration window to be effective.

Underdosing inhibitor in geothermal service does not simply reduce protection proportionally, it can allow corrosion and scaling mechanisms to accelerate that are difficult to reverse once established on piping and heat exchanger surfaces. Overdosing adds chemical cost, but more importantly, some inhibitor formulations become less effective or interact with brine chemistry in undesirable ways at concentrations above the design range.

The physical location of dosing points in a geothermal facility adds another dimension: dosing pumps near wellheads and separators frequently operate in elevated ambient temperature environments, which affects the viscosity of the chemical being dosed and can influence pump performance if the pump’s specification was not reviewed against operating ambient rather than standard laboratory conditions.

The Role of Flow Proportional Dosing in Accuracy

Maintaining accurate chemical concentration requires that dosing rate track actual process flow, not simply run at a fixed rate set during commissioning. In power generation and geothermal applications where flow rates vary with generation output, load following, and operational changes, a pump running at a fixed stroke regardless of flow will overdose at low flow and underdose at high flow.

Flow proportional dosing, where the metering pump’s stroke rate is controlled by a pulse or analog signal from a flow meter on the process line, maintains a constant chemical-to-flow ratio automatically as flow varies. ProMinent’s metering pumps support external pulse control and 4-20mA analog input for this purpose, making integration with plant flow instrumentation straightforward where the control infrastructure is in place.

Calibration and Verification as an Ongoing Practice

Even an accurately specified and correctly installed metering pump drifts over time as diaphragms and valves wear. Establishing a routine calibration verification program, measuring actual output against set point at defined intervals and adjusting or maintaining components as needed, is the practice that keeps a metering pump delivering what its specification intends throughout its service life rather than only at initial commissioning.

ProMinent’s pump designs facilitate field calibration through calibration cylinders or graduated chemical containers that allow actual output measurement directly rather than relying on indirect indicators. This straightforward field verification capability is the practical foundation of any credible dosing accuracy program.

Ultra Power distributes ProMinent’s metering pump range in the Philippines, supporting power plant engineers, geothermal facility operators, and industrial water treatment managers in specifying and maintaining dosing systems that deliver actual chemical accuracy rather than nominal specification. For facilities experiencing unexplained chemistry problems despite running established treatment programs, verifying the actual output of dosing pumps against their set points is frequently the first step that explains what the treatment plan alone cannot.