For pumping thick and viscous liquids, such as grease, bitumen, oil, foodstuffs and other high viscosity substances, specialised types of pumps are used, which have certain design features. Most of them are positive displacement pumps. They provide reliable operation under conditions of high load and high liquid density.
These are pumps with gears as the main working body. The gears are in constant engagement and, when rotating, create a low and high pressure zone, respectively, on the one hand, the product is sucked in and then moved between the gear teeth to the discharge zone.
The advantages of this type of pumping equipment include the ability to suck ‘dry’, without preliminary filling of the working chamber, high efficiency when working with viscous liquids, small size and compact design, reversible operation (ability to change the direction of pumping).
Among the disadvantages, it is worth noting the limited ability to pump liquids with a high content of abrasive particles, solid inclusions that can lead to pump jamming and rapid wear of working elements.
This group of pumps can be divided into two main subgroups:
External gear pumps are easier to manufacture and maintain, but internal gear pumps can handle more viscous liquids.
They consist of a screw-shaped rotor that rotates in a rubber casing, which moves the liquid in the axial direction. This type of pump is suitable for handling high viscosity liquids such as oil, resin, bard, detergents, hydrofuse, minced meat, etc. They provide a smooth and continuous flow.
By changing the screw pitch, cage diameter, and rotation speed, the pump can be tailored to almost any product.
Among the disadvantages are the high cost of manufacturing due to the complexity of the design, large dimensions (even low-capacity pumps are more than 1 m long), the cost of parts, and rapid stator wear in the presence of solid particles in the product.
In these pumps, the liquid is pumped through a flexible hose, with the hose remaining stationary during operation. The hose is sandwiched between the casing and rollers, which, as they rotate, crimp the hose, forcing the product through the hose.
They are often used for pumping aggressive, thick and abrasive liquids, particularly in the chemical and pharmaceutical industries.
Advantages:
They are suitable for pumping thick and abrasive liquids, do not foam the product, and there is no contact between the liquid and the moving parts of the pump, which significantly extends the pump's service life.
Disadvantages:
Quite low working pressure - usually about 1-2 atm.
Rapid wear of the hose, requiring frequent replacement.
These pumps are based on the principle of changing the volume of the working chamber due to the reciprocating movement of the diaphragm.
The diaphragm is mounted on a pneumatic motor stem and driven by compressed air. The pump consists of two working chambers connected by a suction and pressure manifold to ensure uniformity of flow and pulsation. As a result, when one chamber is undergoing a discharge cycle, the second chamber is sucking the product.
The working chamber is equipped with gravity-type valves (i.e. the movement is due to gravity, there are no springs), which allows pumping a variety of products containing suspended particles.
Valves are conventional balls made of stainless steel, rubber or plastic that alternately close and open the entrance to the working chamber when the membrane moves.
The membranes are made of such materials as EPDM, PTFE, Santopren, NBR. The working chamber can be made of PP, PVDF, AL, AISI 304, AISI 316.
