Dosing Pump Dosing Done Differently: Pump Efficiency is Energy Efficiency

Author / Editor: Paul Davis* / Dominik Stephan

A new dosage pump solution offers more than just lower life-cycle costs — Pump efficiency is energy efficiency. But do you have to sacrifice dosing accuracy for energy saving? As power consumption becomes a premier cost factor for pumps, one should consider alternative technologies.

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The Hydra-Cell MT8 opens new doors for metering technology.
The Hydra-Cell MT8 opens new doors for metering technology.
(Bild: Wanner)

As major users of pumps, the chemical as well as the oil and gas industries are concerned with the costs of owning and operating them. Today, continuing rises in the cost of energy have outstripped other elements of Life Cycle Costs. Thus, pump efficiency is the key to energy saving. Since it varies considerably from one type of pump to another, the specifier needs to be alert to differences between basic pump technologies. Metering and dosing is one sector in which such differ­ences are clearly seen.

Flow rate must be accurate, consistent and should be independent of system pressure. In many applications pumps are required to function repetitively over long periods, exposing them to extra risk of energy wastage through loss of efficiency. Poor selection of the metering pump impacts directly on that of the system it serves.

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Pumping with High Accuracy

Where high accuracy is demanded, ‘true’ metering pumps are preferred. Perhaps only two types are widely acknowledged to qualify. Each type is seal-less and designed to be leak-free, operating at low and high discharge pressures, but the two differ in principle — and in the energy they use. Traditional metering pumps offer a variety of designs but are recognizably similar in approach. Pumps of this type have a single large diaphragm per head. That means a large variation, some 323 %, between average and peak volumetric displacement. It leads to widely varying pressure on the suction, increasing acceleration head losses. On the discharge, it can create problems such as cracked pipe connections and leaking chemicals.

Overcoming the Obstacles of Metering and Dosing

The wide differential between average and peak displacement also results in torque variations at pump shaft and motor shaft. As current in a motor is proportional to torque, there is large variation between peak current and root mean square (rms) current; ultimately leading to poor efficiency and much higher energy usage. To deal with these problems, pulsation dampeners are required, with all the associated issues of installation cost, strict monitoring and maintenance.

By contrast, the Hydra-Cell pumps by Wanner Engineering, incorporate three or five small diaphragms flexing sequentially in one head. This construction is fundamental in reducing the energy consumption. Variation between average and peak volumetric displacement is 14 % and 4.4 % respectively. In most systems there is no need for pulsation dampeners. Their cost and associated service and maintenance costs, are minimized or saved.

Low Flow, High Pressure

To apply the full benefits of multi-diaphragm technology to the many systems needing a combination of low-flow and high pressure, Wanner has developed a unique new metering pump — the MT8 which is now ready for sale after a rigorous test programme. The MT8 is designed for high accuracy at flows from 30 down to 0.23 l/h with a maximum outlet pressure of 241 bar. It is the first triplex metering pump (with three diaphragms in one liquid end) able to match these ratings. The pump exceeds API performance standards for Linearity, Repeatability and Steady State Accuracy.

In a detailed formal document from Germany’s internationally-recognised Nano-Saar Laboratories the MT8 was reported to have performed well with all liquids. Tests were conducted at pressures ranging from 10 bar to 220 bar. No blockage occurred. Aqueous and solvent-based pigment preparations were processed through different MJR devices, creating a hydrodynamic pressure before the reaction chamber. The applied pressure creates liquid jets which impinge in the middle of the chamber resulting in high turbulence, impact force and shear. ‘Various organic and inorganic pigments were processed, each at pressures ranging from 10 bar to 220 bar. Carbon blacks, inkjet dispersions and emulsions were also processed.’

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