Milton Roy Metering Pump, a concept that has been following human concerns and values

Patrick Deniau, Business Development Mgr, Milton Roy Europe

Birth of the concept
In a recent press article, it is mentioned that the Egyptians were using a pump close to the metering pump concept, but in real terms, the birth of the concept took place during the XIXth century with the venue of the industrial era and human health concern like increasing need for potable water.

In these processes, quickly appeared the need for pumps, transfer pumps on one hand, precision pumps on the other one, whose purpose was to inject precise and accurate doses of various chemicals.

The first metering (or dosing) pumps were of reciprocating piston type (piston or plunger is in direct contact with the chemical being pumped), whose delivery is not so much dependant upon discharge pressure, with a mechanical device to adjust the piston stroke (when pump is stopped first, when pump is in operation later), with an adapted sealing of lip seal type (in leather, or in elastomeric material later), or packing gland type (breaded cotton).

Schematic drawing of a packed plunger piston pump head

A metering packed plunger pump from the 60’s, with stroke (eccentric) adjustment when pump is stopped

Towards more security
Like all sealing systems between a static part and a dynamic one, lip seal or breaded packing cannot provide a perfect sealing (zero leak). As metering pumps usually pump corrosive mediums (like acids, sodas, etc.), leaks mean corrosion of the equipment and danger for the process personnel like maintenance technicians.

Packed plunger metering pump from the 60’s, partly corroded by leaks

A first evolution towards more security was the development of double packing sealing systems where leak can be collected, drained, and neutralized if necessary.

Schematic drawing of a double packing plunger liquid end

In parallel, manufacturers have investigated the hydraulically actuated diaphragm concept where hydraulic coupling between piston and diaphragm is provided. The seal less and leak proof concept was using stainless steel diaphragms, but its reliability was questionable (life of diaphragm was short, and unpredictable), its cost rather high (small stroke at centre of diaphragm obliging for large diameters), and the level of accuracy difficult to optimize (oil leakage, presence of compressible air in the oil, etc.).

Such a technology also had limitations in terms of maximum working pressure, pumping of slurry or viscous fluids.

When in 1928 DuPont de Nemours invented the PTFE, this was a decisive step. It was then possible to develop the mechanically actuated diaphragm (MAD) concept where the alternative motion is directly transmitted by the piston to a disc of corrosion resistant PTFE. Being sized at its periphery, such a technology was really offering zero leakage design with some other advantages in terms of viscosity limits, and slurry pumping capabilities.

Today the mechanically actuated diaphragm concept is the most used one.

Picture of a MAD pump

Again more security and a touch of environmental friendly
Despite its success, the MAD concept still suffered from its limitation, like a working pressure of less than 20bar. Over this limit, life of the diaphragm is shorten significantly as the diaphragm sees the process pressure on one side when the other one is at atmospheric pressure. Also if the concept was well adapted to smaller outputs, it quickly becomes less to no competitive: larger flows require larger diaphragm, and as it directly impact the end load of the pump, larger drives and larger HP’s.

More and more today, the market is requesting these MAD pumps to be integrated into boxes, called EH&S boxes at Milton Roy.

Picture of a Milton Roy EH&S box, with MAD pumps inside

Getting zero leaks at higher pressures and higher flows, lead manufacturers to use PTFE for hydraulic actuated diaphragm (HAD) designs. Knowing the drawbacks of the HAD technology, and due to the low mechanical resistance of the PTFE, the HAD concepts developed at this time were using contour plates to handle the movement of the PTFE disc between two physical limits, and liquid ends were equipped with an internal pressure relief valve. An air bleed valve was also added to make the pump concept more reliable.

Today the HAD technology has moved steps forward, with air bleed and internal pressure relief valves integrated, the use of mechanically actuated oil refill systems that prevent the use of the process side contour plate (giving access to application where fluids are viscous, or pumping slurry). Latest evolution is the double or multiple diaphragm concept that allow the pump to continue to work when one diaphragm fails, and provide the customer with a diaphragm failure alarm. In the mid 70’s, appeared moulded and pre-shaped diaphragm where PTFE (process side) adheres to a moulded elastomeric support (oil side of the diaphragm); this technology authorizes smaller diameters (diaphragm rolls when moving), and diaphragms can be re-used after liquid end disassembling, a first step toward ecodesign.

Schematic drawing of a double HAD pump head: air bleed and internal PRV valve, oil refill system, diaphragm and failure detection

Today, eco-design is in the heart of new developments
When in 2005 Milton Roy Europe is given the project of completing its product offering, the R&D team did benchmark several existing concepts, taking into account notions like:

• Cost
• Compactness
• Weight
• Number of parts
• Footprint
• Painted surface
• Oil volumes
• Transmissible power.

The new compact and patented Primeroy pump concept is launched to the market in 2007 (first model). Its eco-design process can be translated into figures when comparing with the previous offering based on the Milroyal range.

At raw materials level, the pump needs 40% less energy, it saves emission of 160kg of equivalent CO2 and impact on human toxicity is reduced by 37%.

With a gain of 43% in weight and 46% in volume, the impact on transportation, even difficult to size as product destinations are various, is certain and significant.

On a typical 20 years of life, the use of oil is reduced by half, saving 500 litters of oil per each pump installed.

At end of life, the pump can be recycled at 95% in mass (suppression of glue in assemblies), and its painted surface is reduced by nearly 30%.

If eco-design is in these days, we can see through these figures that it is a pertinent approach, even economically speaking for both the manufacturer and the end user.

Picture of the Primeroy® K pump

Results obtained by the use of the ‘Bilan Produits’ software developed by ‘University of Cergy Pontoise’ (FR)