Centrifugal Plastic Pumps
If the concern is corrosion resistance when handling liquids, centrifugal pumps made of special materials are just the thing. Plastic centrifugal pumps, also called plastic pumps for short, have proven themselves especially well here. With materials such as polypropylene and PVDF, they are resistant to even aggressive acids and other chemicals.
Frequently, a pump with a plastic casing is associated with the term “Plastic (centrifugal) pump.” There are such pumps, but they are most popular in the private sector for small applications – usually as cheap pond or garden pumps from home improvement stores. By contrast, industrial plastic pumps generally have robust, metallic outer casings but their interior is either lined with plastic or consists entirely of components manufactured of plastic.
Hermetically sealed plastic pump (MUNSCH CM series).
All wetted parts are from plastic.
Technical Data of the available Plastic Centrifugal Pumps
Flow rate: up to 3.000 m³/h (13.200 gpm)
Delivery Head: up to 100 m (330 ft)
Operating pressure: up to 16 bar
Operating temperature: up to 180°C (356°F)
Viscosity: up to 300 mm²/s
How a Plastic Centrifugal Pump works
As the name suggests, the plastic centrifugal pump belongs to the group of centrifugal pumps and is based on the radial pump. Like in any other centrifugal pump the liquid entering the pump casing is being accelerated by the rotating impeller. At the discharge of a volute casing speed is being converted into pressure. Impeller and volute casing have to match each other to create the best efficient hydraulic unit of the pump. The larger the impeller diameter and speed are, the larger the pressure difference will be and the wider the impeller and volute are the higher the flow of the pump will be.
Most pumps are driven by electric motors. This is not at all different with plastic pumps. The energy a pump requires has a linear increase with pressure and flow. The motor transmits the energy through the pump shaft to the impeller but not all of it is converted into pressure. Energy losses are created by friction on bearings and hydraulic imperfections such as vortexes and backflow. Manufacturers of high quality pumps put considerable efforts into hydraulic R&D in order to minimize these losses. Today those high-quality plastic pumps achieve efficiencies up to 80%.
Plastic pumps specialize in corrosive fluids
Plastic pumps are viewed critically in many industries, now as before. Here, robust centrifugal pumps are used successfully in many demanding sectors; in fine and basic chemistry, for example, they are indispensable. Among the fluids for which plastic centrifugal pumps have proven themselves are:
- Hydrochloric acid
- Sulfuric acid
- Nitric acid
- Hydrofluoric acid
- Phosphoric acid
- Flurosilicic acid
- Chlorine and media containing chlorine
- Salt water, brine
and several more. The list is long.
The selection of pumps made of plastics such as PFA, PP (polypropylene) or PVDF (polyvinylideflouride) is huge. For fluid quantities from a few liters to several thousand cubic meters per hour, there are numerous manufacturers around the world. Here, specialists and series manufacturers have established themselves equally. While in the giant segment of small pumps (up to about 1 m³/h) there are many dealers offering standardized solutions, with increasing requirements and pump sizes, manufacturers have had to develop products attuned to the industry in question and fulfill special requirements for documentation and production.
Pumps that work according to the positive displacement principle (membrane pumps, for example) are best suited for very small handling quantities or for dosing liquids. However, the broad spectrum of handling quantities is served by centrifugal pumps. Even if the design and handling characteristics are completely different, here all parts in contact with the media are made of plastic.
What specifications do plastic centrifugal pumps have to fulfill?
For pumps that are used in dangerous or challenging industrial processes, there are frequently rules and precise specifications. Manufacturers of plastic centrifugal pumps that serve these industrial areas comply with these rules, as do manufacturers of metal pumps. The rules function as safety measures, which protect the pump against damage and simultaneously protect the environment as well: for example, by ensuring that no toxic or environmentally harmful materials can escape. The rules that have to be complied with include the EU machine directive, the ATEX directive, ISO 5199 and ISO 2858.
An example of practical safety measures for plastic pumps is the design as magnet-coupled pump: Here, the interior materials are massive plastic and silicon carbide ceramic, while the exterior cast-iron shell provides pressure stability and protects the pump against external influences. With a magnetically coupled pump, the fluid to be handled is hermetically sealed off from the environment. For many areas of application, however, models with a mechanical seal are completely sufficient.
Advantages and disadvantages of plastic pumps and metal pumps
✔️ Universally resistant to chemicals and salt water
✔️ Spiral casing can be replaced
✔️ Short delivery times
❌ Only suitable for temperatures up to 200 °C
✔️ Very efficient
✔️ Cost-effective when using standard material
✔️ Wide variety of manufacturers
❌ Long delivery times with special metals
✔️ Suitable for temperatures over 200 °C
❌ Very expensive when using high-alloyed metals
Material types for plastic pumps
Four factors have to be considered for the selection of materials:
- Chemical resistance
- Wear resistance
- Temperature resistance
The most resistant plastics that are used as material for centrifugal pumps are the thermoplastic UHMW-PE (ultra-high molecular polyethylene) and PFA (perfluoralkoxy-polymer). As with metal pumps, requirements for the operation and pump properties have to match. Here, economic factors also play a role: Just as a metal pump with parts in contact with media does not always have to be made of expensive Hastelloy, for many areas of application for which plastic pumps are predestined, PP or PVDF are completely sufficient as materials.
If the application temperature, pump capacity, and pressure requirements allow, plastic pumps can be used everywhere where fluids are corrosive. This begins with salt water and includes most inorganic acids and acidic fluids. And plastic pumps also handle alkalis without a problem.
Which manufacturers sell plastic centrifugal pumps?
Especially with large components that can weigh more than 100 kilograms, the manufacturing process of the plastic parts for pumps is very time-consuming. As with casting of special alloys, it requires a great deal of knowledge. These time-consuming manufacturing processes are also the reason the number of manufacturers is smaller and standardized pumps are not the same as the custom-tailored large pumps. Especially for industrial applications, there is therefore a reasonably small number of specialized manufacturers of plastic pumps.
One of these specialized manufacturers, which is also a SPA member, is the chemical pump manufacturer MUNSCH, which has specialized in the manufacturing of especially robust plastic centrifugal pumps for all challenging fluids handled and whose pumps are available in different models and designs, also as norm pump.