A short history of the dosing pump
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uction pressures as low as 7 Torr.
Piston diaphragms
In industrial applications, where high pressures are likely to be encountered, the piston-diaphragm technology rapidly took a predominant position. In this type of pump, the piston is hydraulically coupled to a diaphragm, which is in contact with the process fluid (Figure 3). Here the diaphragm is only a separator and is pressure balanced. Typically, it can handle pressures up to 400bar and some technologies, the pre-shaped composite being an example, can give an operational life in excess of 20,000 hours.
This design considerably less limited in terms of slurry handling and has about the same capability to pump viscous fluid when compared to the packed plunger type. As the main limitation has been the ability to pump in high temperature conditions, the market is now offered alternatives with metallic diaphragm heads.
Current generation
Today, the state-of-the-art for process industries (chemical, oil extraction, food) is the double diaphragm configuration with diaphragm failure detection, as this offers greater levels of safety and zero emission. Some studies have been undertaken showing that if the capital cost is more important than for a packed plunger pump, the total cost over five years including maintenance gives a competitive edge to the diaphragm technology. Only in developing countries, is there still a noted preference for packed plungers, as these are seen as easier to maintain.
In parallel with this move from packed plunger toward diaphragm technologies, another major improvement took place in the 1970’s. For small pumps, i.e. pumps needing fractional horsepower, the reciprocating motion of a dosing pump became obtainable from a solenoid with acceptable pump life and reliability.
This technology lead to a more simple and lower cost design of pump and it rapidly became a worldwide standard in utility applications. This was helped by the possibility, for almost no extra cost, of providing either variable stroking speed or automated proportional function due to the electronic circuit board required to pulse the solenoid. Compared to the motor driven pump, this was a huge improvement in terms of pump capability and versatility. More recently, with the development of technical plastics suitable for the pump housing, this technology has gained both in cost efficiency and in corrosion resistance. Today, in terms of the number of units sold, solenoid dosing pump is the most popular design, by far.