Do you know what a plastic pump is for and when it is advisable to have one in your process? Do plastic pumps also pump plastic or only other fluids? Read on and learn where non-metallic pumps are unbeatable and what their differences and limits are.
The selection of pumps made of plastics is confusingly large. Flows start from just a few liters up to several thousand cubes per hour and manufacturers are to be found around the globe. Both, specialized companies as well as serial producers are long established in their individual markets. While the larger segment of small pumps (less than one cube per hour) is mostly covered by standardized pumps we see an increasing amount of special requests for which specialized pump manufacturers provide individual pump solutions.
Other than sometimes anticipated the material plastic is not a synonym for “cheap material”. Pump manufacturers know that specifications and decisions are sometimes based on this misconception, where metal pumps are always considered to be from superior quality. In fact plastic pumps today offer a surprisingly reliable and economical pump solution not just equal but often superior to those of metal pumps.
For very small flows and dosing requirements, the use of displacement pumps (i.e. diaphragm pumps) is often recommended. Though, the largest range of flow is being covered by centrifugal pumps (also: ra-dial pumps). These pumps can differ in design and characteristics but in general all wetted parts are made of or covered with plastics.
As far as the operating temperature and pressure allows for, plastic pumps take the lead wherever the pumped fluid is corrosive. This can be just salt water or any inorganic acids and acidic liquids. Even alka-lis can be handled easily. The list of successful plastic pump applications is rather long - you will probably be surprised!
The selection of metals being used as a pump material requires a high-level expertise, often linked to the specific application. Even with the correct selection, metals are then often limited in terms of fluid com-positions and temperatures. Plastic pumps however usually cover a wide range of chemicals and tem-peratures. They even outperform their metal companions when it comes to abrasive fluids – a property that is often underestimated! A metal optimized towards corrosion resistance is likely to have weak-nesses on abrasion resistance (i.e. metals with increased Nickel content).
Erosion corrosion, pitting or crevice corrosion, all common forms of corrosion in metal pumps, are un-known to plastic pumps. Just the three of them add up to a major part of the worldwide pump repair budgets for metal pumps. However, it is very likely you can find a matching pump from plastics.
Even in innocent looking applications with slightly acidic liquids, where pH sometimes drops or the chlo-rides increase, pumps from plastic have proven successful for decades and saved operators from maintenance costs and downtimes.
Safety is of paramount interest in almost all applications. But what does it specifically mean for a pump handling a dangerous liquid? The most common answer is ‘The pump has to be tight’. While displacement pumps mostly use static seal elements (such as o-rings, gaskets) radial pumps use dynamic seals (i.e. mechanical seals). In any case, including sealless pumps, operational safety strongly depends on how the pumps are being operated, installed and controlled. Pump manufacturers – including those of plastic pumps – do know the limits of their individual pumps very well. In fact, those suppliers with a high spe-cialization and application expertise usually aim to get in touch with the operators and planners to find the best pump fit and the right protection equipment for their individual installations.
Centrifugal pumps from plastics are available in a vast amount of sizes and seal technologies. A large part of them even follows common industrial standards (among them ISO 5199, 2858, 15783 or 9906). They are, in terms of sizes and performance, comparable with their metallic kinship – without exception.
However, in very high and very low temperatures (more than 200°C or less than -20°C) even the best plastic pumps are at their limit. This is in fact the reason why plastic pumps do not pump plastic at all, because this requires much higher temperatures. While fluoropolymers (PVDF, ETFE, and PFA) are good for up to 200°C, the thermoplastics PP and UHMW-PE, otherwise known for their outstanding rugged-ness, are restricted to 100°C. As the temperature of the fluid increases the allowable pressure of a plas-tic pump decreases. However, in very high and very low temperatures (more than 200°C or less than -20°C) even the best plastic pumps are at their limit. This is in fact the reason why plastic pumps do not pump plastic at all, because this requires much higher temperatures. While fluoropolymers (PVDF, ETFE, and PFA) are good for up to 200°C, the thermoplastics PP and UHMW-PE, otherwise known for their outstanding rugged-ness, are restricted to 100°C. As the temperature of the fluid increases the allowable pressure of a plas-tic pump decreases.