Pumps for abrasive liquids must have peculiar characteristics: in this article we will see what they are and what PEMO PUMPS offers for this purpose.
Pumping abrasive liquids requires special attention in the choice of pump. In fact, you need to identify the most suitable system to transport the fluid in the most efficient way, reducing wear, maintenance costs and necessary rest times.
Normally, by abrasive liquid we mean a fluid that carries refractory material divided into more or less fine particles: it can be limestone, clay, paint pigments, coal, metal particles or much more. This type of abrasive liquid exerts a particular stress on the pump, due to the erosion it causes by physical friction or chemical reaction.
There are many industrial sectors that require pumps for abrasive liquids: from wastewater treatment plants to those for galvanic surface treatment, from metallurgical plants to the chemical and food industries.
All these areas require pumps for abrasive liquids that meet the technical requirements defined by the legislation and Community directives for the sector concerned.
Abrasive liquid pumping
Pumping abrasive liquid causes wear on the pumps themselves. It is determined by the characteristics of the solid particles which are in the pumped fluid, by their concentration and viscosity of the liquid, as well as by the materials used for the construction of the pump and by the conditions in which it operates, in particular by the speed and pressure it exerts.
The harder a material, the greater the risk of wear during pumping.
The hardness of solids is measured using the Mohs scale, which goes from 1 (talc) to 10 (diamond): during pumping, pumps are exposed to the greatest risk of deterioration due to materials that exceed 6 on the Mohs scale.
In addition to hardness, the shape and size of the abrasive particles are also important factors: beyond a certain diameter, use can become extreme even if the scraping material is present in low concentration in the transported abrasive liquid.
The viscosity of the liquid that carries the solids also helps to determine the degree of damage. If it is higher it is less aggressive for the moving and static components of the pump, because it softens the impact of each abrasive particle. Sand in oil, for example, abrades less than sand in water.
The conditions under which this type of pumps operate are just as important and significantly affect the use and life of the tool. A higher speed or differential pressure makes the impact between the scraping particles and the pump components much more energetic and wearing.
For pumping abrasive liquids, manufacturers tend to recommend larger pumps, which can operate at lower speeds and differential pressures. For a higher initial investment, maintenance and replacement costs are less in the long run.
Types of pumps for abrasive liquids
Not all types of pumps can operate with abrasive liquids.
Gear ones, for example, work with very close tolerances and risk of wear or damage from sub-millimetre solid particles. Types of pumps with internal gears are more durable since they only have one or two bearings exposed to the fluid. A gear pump should still have a filter installed on the suction side, to be protected from potentially harmful solids.
The various types of centrifugal pumps are commonly used although the high operating speeds can wear out the impellers. This requires special attention in the choice of seals and bearings, especially in the case of dangerous fluids. In applications with abrasive liquid, mechanical seals are normally preferred: the space between the sealing faces can be reduced to prevent access to solid particles that could damage them.
The PEMO PUMPS range includes different types of vertical pumps that are suitable for pumping abrasive liquids, in particular in the following series:
- JOLLY, designed to pump acid liquids even with a high concentration of scraping particles;
- MEC, for any highly abrasive and acidic liquid with or without abrasive suspensions;
- AUS, designed to operate in the most severe conditions, with intermittent flow, also suitable for dry operation.
Also other types of the PEMO PUMPS range can possibly work with abrasive liquids, even though they have not been designed primarily for this purpose:
- AO / TD, designed for heavy slurries and / or acid applications, perfect for pumping acids and abrasive liquids with high concentrations of scraping particles;
- AO / AB, for applications on sludge and / or acids, also fitting for acids and abrasive liquids with high concentrations of scraping particles, as long as they are smaller than 2 mm;
- AO / AB / DC-TC types which are suitable for an abrasive liquid with high concentration of scraping particles in applications in which the required discharge pressure is up to 20 bar (290 psi): unsuitable if the particle size is greater than 2 mm.
Characteristics of pumps for abrasive liquids
Let’s see in more detail the characteristics of the models that PEMO PUMPS offers for pumping abrasive liquids:
The JOLLY series pumps for abrasive liquids are built to be resistant.
The shafts are supported above the base plate by two or three bearings so that the bottom is suspended and works without any other bearings or supports. The submerged parts and the internal parts of the casings and impeller are coated in rubber or hard alloy (700 ÷ 800 HB).
Jolly pump shafts are designed according to the immersion length and the maximum head of the pump. This eliminates any vibration and also protects the lower part of the pump. It will only be necessary to change the guide bush and the sleeve that are worn by abrasive liquids at intervals of time that depend on the size of the particles in the abrasive liquid to be pumped and on the total head of pump operation.
The Jolly series pumps for abrasive liquids are designed for fixed installation or suitable for barges. They have a heavy duty mounting plate, with bolt holes and lifting eye bolts.
The pumps for abrasive liquids of the MEC series are substantially similar to the Jolly ones, but are not mounted on cantilever brackets. At their top a sturdy metal structure with a lifting eye bolt (to which a wire rope, chain or any other suspension device can be attached) allows them to be kept in a vertical position inside tanks or wells and to be easily moved from a position to the other.
From a mechanical point of view the pumps for abrasive liquids of the AUS series are also similar to those of the JOLLY ones.
Their main feature is the particular design of the casing-impeller body, which allows them to run dry. They are also very easy to care for: greasing the bearings is practically the only maintenance required.
The result is a pump capable of operating even in extreme conditions.