Chemical plastic pumps and abrasive-containing liquids
Manufacturers of pumping equipment for the chemical industry are increasingly giving preference to polymers when choosing materials for their products. This is due to their extreme resistance to aggressive chemicals and adaptability, and sometimes their relative cheapness relative to metals. Plastic pumps are much lighter than metal samples. At the same time, they have sufficient strength to work with engines up to 3000 rpm and significant performance.
Currently, the main types of chemical pumps are centrifugal and diaphragm pumps.
Modern centrifugal pumps are mainly pumps with a special mechanical seal and pumps with a magnetic coupling.
Horizontal polymer chemical centrifugal pumps have high performance, are powered by a direct drive motor (Max. 3000 rpm), and are designed for fast pumping and/or pumping of aggressive liquids at a flow rate of 9 to 40 m3/h.
If the impeller is open, the pump can pump even very polluted liquids containing small suspended dense particles in a continuous flow.
Special chemically resistant mechanical seals make it possible to prevent the leakage of aggressive solutions of chemicals from the pump part and damage to the engine. They are made of polymers for use in standard conditions. For heavy – duty applications and heavily soiled liquids, use Teflon and friction pairs made of ceramic or silicon carbide.
The Relative Strength of polymer materials made it possible to produce new types of pumps – plastic pumps with a magnetic coupling.
Magnetic coupling centrifugal pumps are used in processes where aggressive reagents and solutions require circulation or pumping.
The magnet on the motor shaft rotates the magnet integrated into the pump impeller with its magnetic field. Therefore, there is no need for shaft seals, since aggressive liquid does not come into contact with it. There is no need for expensive shaft material made of special resistant alloys. This significantly reduces operating costs
Magnetic coupling pumps are designed for fast pumping and/or pumping of aggressive liquids at Flow rates from 15 to 1230 l/min (0.9 - 73.8 m3/h). Magnetic coupling pumps are used for pumping clean liquids with a viscosity of up to 200 cPs (at 20 °C).
In general, plastics are not sufficiently resistant to liquids containing abrasive particles. Only a few of them are as abrasive-resistant as stainless and carbon steel.
Relative bulk abrasive abrasion of various materials (PE-1000 - 100 abrasion) according to the abrasive wear test method in the abrasive mixture (ISO 15527).
Therefore, only PVDF (polyvinyldene fluoride) and PE-100, PE-HD (polyethylene) can compete with metals in terms of abrasive resistance.
A large amount of abrasives and solid particles in the liquid lead to rapid failure of plastic pumps with a magnetic coupling.
Special pre-filters should be used to filter coarse particles.
The coarse pre-filter is designed to install pneumatic or centrifugal pumps to protect them from suspended solids and foreign objects, without causing excessive loss of productivity.
The basket filter is an important device for protecting the pump. Thanks to its use, suspended particles, filaments contained in the liquid are filtered. These elements are particularly harmful to pumps. The kit does not contain metal parts and is therefore ideal for highly aggressive substances such as acids and alkalis used in the chemical industry. The filter structure makes it easy to clean and inspect.
Plastic diaphragm pumpsare also suitable for abrasive-containing viscous liquids and liquids with dense particles.
Special slurry (mud) pumps are better able to cope with these tasks.
The flow part of the slurry pump is made of a high-chromium alloy or coated with wear-resistant rubber, which makes them suitable for liquids containing solid particles, as well as acids or alkalis, which makes it possible to use these pumps for a wide range of liquids.
Centrifugal slurry pumps are used for pumping abrasive liquids with a high concentration of suspended particles. Pumps have different types of construction: horizontal self-priming, semi-submersible, submerged.
In difficult operating conditions special rubber lined chemical pumpsare used, as well as pumps with a working part made of thick-walled cast acid-resistant stainless steel AISI 316L.