Design and principle of operation of a screw pump

Screw pumps are positive displacement pumps. There are other names for these pumps: screw, gerotor, worm and eccentric pumps.

Screw pumps are a type of rotary-gear pumps and are conventionally divided into single-screw and multi-screw. A multi-screw pump is one in which the main drive screw (rotor) is helically meshed with one or more driven screws. When the drive screw rotates, the driven screws also begin to rotate. Multiscrew pumps have a higher efficiency and the ability to create higher outlet pressure. In this article we will look at the operating principle and design of pumps that are most often used in industrial production - single-screw pumps.

Single-screw pumps can be divided into high-performance pumps for pumping large volumes of product and screw pumps for barrels, Eurocubes and other mobile containers. The main difference between these two types is their purpose. The former have a massive structure and are designed to pump a large volume of liquid without immersing any of its parts in the container. The latter, on the contrary, have in their design a submersible part of such a diameter that can be installed in the filler hole of the barrel. However, these pumps have a similar design, are self-priming and are capable of pumping viscous liquids.

Let's consider the design and operating principle of a screw pump. Any screw pump can be divided into two parts. The first part drives the working body of the pump, thereby causing the pump to pump liquid. It includes a motor and gearbox. The second is the mechanical part of the pump, thanks to which the liquid is pumped with a certain performance and pressure.

Pump motor and gearbox

Closed-type asynchronous electric motors are most often used to drive a screw pump. The electric motor power can reach 15-20 kW, and the shaft rotation speed varies from 300 to 1500 rpm. Many manufacturers of screw pumps can offer a pump with an electric motor, which is equipped with a frequency converter. If the frequency converter is of a standard type, then it is usually mounted on the vertical part of the trolley, on which the screw pump itself is located. This is done for those cases when it is necessary to pump liquid from different containers with one pump. In the case when there is no need to move the pump, it is installed permanently and in this case frequency converters with a wireless control unit are used.

As a rule, all screw pumps are equipped with reduction gears in their design. The gearbox is the connecting link between the engine and the mechanical part. It serves to change the number of revolutions coming from the electric motor to the pump itself. A reduction gear reduces the number of revolutions and increases torque. Sometimes there are gearboxes that can change the direction of rotation of the electric motor shaft. The amount of torque is very important when the pumped liquid has high viscosity and density. Structurally, the gearbox consists of several gear wheels that are in sequential engagement with each other, despite the fact that the diameter of the wheel on the electric motor side is always smaller than the diameter of the wheel on the pump side. That is why the output gearbox always has more torque and lower angular velocity. Together, the electric motor and gearbox are called a gearmotor.

The most important characteristic in this case is the gear ratio. It shows how many times the torque has increased and how many times the speed transmitted by the electric motor has decreased. Manufacturers of screw pumps offer geared motors with different gear ratios that are suitable for almost any task. When selecting a gear motor, you should adhere to the following rule: the higher the viscosity and density of the pumped product, the higher the gear ratio should be, because in this case there will be a high torque and a lower angular speed of the pump working body. The pump will be able to draw viscous liquid from the container into the working chamber without overloading the electric motor. Here, the power of the electric motor itself is also no less important, because the liquid still needs to be supplied over a distance. However, the required pump pressure is determined not only by the power of the electric motor, but also by the design features of the mechanical part.

In addition to electric motors, screw pumps are equipped with pneumatic motors powered by compressed air. They are usually found on vertical drum pumps and are similar in design to the air motors of centrifugal drum pumps.

How best to use

When purchasing a screw pump for an equipped source, you will have to take into account certain operating rules. By following simple recommendations, the homeowner will be able to significantly extend the life of the device.

To operate a screw pump in a well, it is advisable to select a pump that can be well mounted on the wall of the shaft. It is advisable to install the device at an optimal depth so that the likelihood of the water level dropping to a critical level is minimal. This will prevent the device from running dry.

It is advisable to maintain a distance of at least 1 meter from the bottom so that liquid mixed with sand is not pumped through the water supply. When purchasing a screw unit, you don’t have to worry about the reliability of the operation of such equipment. The design of the product and the basic principle of operation were specially developed in such a way that the water intake hole was located above the engine itself. The working unit, thanks to this design, can be cooled naturally. The probability of fire in this case is practically zero.

Features of water intake are decisive in the selection of functional characteristics of equipment. Before selecting a suitable pump, be sure to take into account all the required control parameters.

Mechanical part

The main components of the mechanical part of a screw pump can be considered the rotor (1), stator (2), pump housing (3), bearing housing (4), mechanical seal (5) and universal joint (6). All these parts are connected in series to each other and are located inside special supports (7).

The driveshaft, also called the “thrust”, has hinges at both ends. One hinge, through the adapter shaft, connects the “rod” to the gear motor, the second hinge to the pump rotor. The cardan shaft is the connecting link for transmitting torque from the engine to the rotor. In addition, since the cardan shaft has a hinged connection, torque can be transmitted at an angle relative to the axis of the electric motor shaft. To prevent the hinge mechanism from coming into contact with the pumped liquid during pump operation, they are placed in special sealed casings made of the same material as the “rod”.

The driveshaft is located inside a cylinder, which is the pump housing. The housing is connected by flanges, on the one hand, to the pump stator, and on the other hand to the bearing housing.

On top of the pump body there is a pressure pipe, which can have a threaded or flanged connection. Since screw pumps can pump liquid reversely, this pipe may well not be a supply pipe, but a suction pipe. In addition, the pump nozzle comes in the form of a loading funnel.

Loading funnels (or hopper) are used when the pumped product has a high viscosity, is pasty, and does not have flow properties. In these cases, the cardan shaft is replaced with an auxiliary transport (feed) auger, which also has a swivel joint. In addition to transmitting torque, the auxiliary screw moves the product loaded into the funnel to the gerotor pair.

The gerotor pair is the most important component of a screw pump, which consists of a moving part - the rotor and a stationary part - the stator. The stator is a steel sleeve in the inner part, which has a spiral-shaped uniform elastomer layer obtained as a result of the vulcanization process. The metal of the stator housing and the inner elastomer layer are inseparably connected to each other. Depending on the purpose of the gerotor pair, the stator can be made of various materials. In a screw pump, the stator is sometimes called a cage and sleeve, and the rotor is called a screw, auger, or worm. The rotor is a screw that rotates inside the stator.

The rotor is a single piece, but it can be roughly divided into two parts. The first part is the head for attaching the rotor to the cardan shaft. The second is the rotor body itself, which has the shape of a spiral and is in constant contact with the holder during pump operation. The stator and rotor are a friction pair with internal cycloidal engagement. The gerotor pair of the screw pump is attached with flanges to the pump body. At the end, depending on the direction of rotation of the rotor, it has a suction or supply pipe.

To seal the pump drive, the design provides a mechanical seal. It is located between the “rod” hinge and the bearing housing.

The bearing housing is a unit consisting of two angular contact bearings and an adapter shaft, which, on the one hand, is connected to the gear motor using a key or splines, and on the other hand, it is pivotally connected to the driveshaft.

A horizontal screw pump can be designed with a bypass. This modification of the pump is used when a flow control device (for example, a solenoid valve) is additionally installed in the pressure line. The bypass allows you to avoid switching off the pump motor every time the valve in the supply line closes. When the valve is closed, the pump continues to operate and pumps liquid in a circle from the pressure pipe back to the suction pipe, thereby avoiding excess pressure in the area from the pump to the valve.

Scope of application of the screw

At its core, a screw is a solid rod with a solid helical surface located along the longitudinal axis. The auger owes its origin to the great scientist Archimedes, who invented a water-lifting machine, which was called the Archimedes screw.

Before using the screw pump, you must carefully study the instructions.

Nowadays, screws are used everywhere and in a wide variety of industries:

A meat grinder is one of the simplest and most common devices using an auger;
Screw conveyors;
Screw pumps;
All-terrain vehicle - ShN-1 auger;
Drilling mechanisms;
Ice fishing enthusiasts use an auger to drill a hole in the river ice;
The auger principle is used in drills to remove chips during operation;
Used in small arms in auger magazines;
Widely used in presses;
Often used in combines for various purposes.

The operating principle of the auger is so simple that it can be used everywhere, and examples can be given endlessly. Needless to say, even in science fiction works there are machines that use screw mechanisms. For example, miracle machines that drill through the thickness of mountains or pierce almost right through the bowels of planets.

Pump operating principle

The pump is connected to an electrical circuit or pneumatic line. When the pump is turned on, the electric motor shaft begins to rotate at a certain number of revolutions per minute. The rotation of the electric motor shaft is transmitted through a coupling connection to the gearbox shaft. The gear wheels of the gearbox, which are in sequential engagement, reduce the number of revolutions at the output of the gearbox and increase the torque. Through the adapter shaft located in the bearing assembly, the angular speed of the gear motor is transmitted to the cardan shaft or transport auger, which in turn drives the pump rotor through a swivel joint.

Let's consider the variant of operation of a screw pump, where the pipe on the side of the gerotor pair is suction, and the pipe on the side of the pump body is pressure. The direction of rotation of the moving parts of the pump occurs in accordance with this diagram (from right to left or counterclockwise, if you look at the end of the rotor from the liquid suction side). The screw rotates in the stator. Since the center of rotation of the rotor is shifted relative to the central axis of the stator by the amount of eccentricity, and the elastomeric layer of the stator has a spiral shape, a vacuum cavity is formed on the side of the liquid inlet into the pump. Liquid is sucked into this space. The rotor turns 90 degrees and this cavity with the liquid in it is hermetically closed while the liquid itself moves inside the stator of the gerotor pair. When the stator is rotated 90 degrees, in addition to closing the cavity with liquid, a new discharged cavity is formed, into which a certain volume of liquid enters.

With each subsequent rotation of the screw, a new portion of liquid enters the gerotor pair, and the previously received liquid receives more and more movement. Since the rotor body also has a spiral shape along its entire length, in conjunction with the stator it forms several closed volumes. It is through these volumes that the liquid moves when the rotor rotates, moving away from the suction point, and since these cavities are sealed, the pumped liquid cannot flow back to the suction side. Next, the pumped liquid under pressure enters the pump housing from the gerotor pair and exits the pump through the pressure pipe. If the moving parts of the pump rotate clockwise, then the pipe of the pump housing is suction, and the pipe of the gerotor pair is discharge.

DIY making

At all times, there have been craftsmen who prefer to do everything themselves and trust only those things that they made with their own hands. Screw devices are no exception.

A homemade concrete pump or water pump is a fairly common occurrence.

Regardless of how the thing was made - with your own hands or in a specialized production facility, the manufacturing technology is not much different, and it must be. It is unlikely that it will be possible to make a screw pump on a whim.

Therefore, before making a screw pump, you should know how to do it:

Since creating a concrete pump is a rather expensive and complex process, you should be one hundred percent sure that making it yourself will be more expedient than buying or renting a ready-made model.
Like any complex technical mechanism, it should be manufactured according to a pre-drawn drawing. You can find a ready-made drawing or design it yourself if you have the appropriate skills.
The key element in a concrete pump is the working cylinder with a piston. You should not take a cylinder larger than 400 mm with a piston stroke of no more than 0.5 m.
In order for the device to serve effectively and for a long time, parts should be manufactured with high precision and low roughness.
When choosing, you should remember that a hydraulic pump will be much more expensive and more difficult to manufacture than an electric pump.
The correct choice of gearbox is one of the key manufacturing procedures.

To assemble screw pumps with your own hands, you need to have the appropriate experience.
To make check valves, you should use alloy steel. Also, do not forget about using a king pin.

Geometry of gerotor pairs

The performance of a screw pump depends on the volume of the closed cavities of the gerotor pair and the speed of the gear motor, and the pressure created by the pump depends on the number of closed cavities per unit length of the gerotor pair and the power of the electric motor. Since the characteristics of a screw pump largely depend on the geometry of the gerotor pairs, we will consider this issue in more detail.

There are several design geometric factors that directly affect the output characteristics of a progressive cavity pump, as well as the limitations of their use. Such factors can be considered: the number of closed cavities of the gerotor pair, the cross-sectional diameter of the rotor (and stator, respectively), the volume of closed cavities between the rotor and stator.

With equal length of the gerotor pair, various modifications are possible in terms of the number of closed cavities. For example, let's consider two versions of a screw pair with the same diameter and equal length. The option with a large number of closed volumes has a smooth supply of product due to the relatively low flow rate at an increased pressure value, as well as high suction capacity. In addition, due to the increased inlet cross-sectional area, larger particles can be pumped. It is also worth noting that this design of the gerotor pair eliminates as much as possible the possibility of liquid leakage from it after the pump is stopped. The advantage of a design with fewer closed volumes is high productivity. This is due to the fact that the volume of each specific cavity, in this case, is larger than in the first option. This design has high volumetric characteristics with a long turnaround time due to the long contact line between the rotor and stator. Therefore, when designing and selecting a screw pump for a particular consumer task, it is first necessary to be guided by the geometry of the gerotor pair and the characteristics of the geared motor.

Disadvantages of screw pumps

When analyzing screw pumps, you need to take a differentiated approach to this issue, since some advantages and disadvantages depend on the chosen model and operating conditions.

Screw pump for well.

In total, for all screw structures, the following remarks should be noted:

Inability to idle. This problem only appears when the well budget is reduced.
Low efficiency. Indicators for different models range from 50-70%.
Unregulated volume of resource supply.
High or low price. It is difficult to take an unambiguous view of these indicators. Budget devices are characterized by increased wear of contacting surfaces, overheating and a short service life. Powerful, good quality equipment will cost comparatively more.

Materials of screw pump parts

The casing parts of the screw pump, which include the pump housing with pipes and the stator housing, are made of stainless steel or cast iron. Since pumps are often used in the food industry, and the housing material is in direct contact with the pumped medium, food grade stainless steel is used for manufacturing (as a rule, it is low-carbon austenitic steel AISI 304 (08Х18Н10 and its varieties depending on the number of alloying elements). In other cases, they use malleable cast iron with a flake form of graphite. This type of cast iron, among others, has the greatest ductility, which minimizes the formation and development of cracks during operation, provides high corrosion resistance. The internal part of the stator is made of elastomeric materials NBR - synthetic polymer (nitrile butadiene rubber ), EPDM is a synthetic elastomer (ethylene-propylene rubber). Barrel screw pumps often have a spiral-shaped internal part made of the universal fluoroplastic material PTFE (polytetrafluoroethylene). This material is chemically resistant to almost any aggressive liquid, as well as to low and high temperatures . This soft plastic material also has low adhesive properties. The rotation parts (propeller shaft and rotor), as well as the protective housing of the swivel joint, are made of stainless steel.

Types and main technical characteristics

All devices of the type under consideration are divided into two main categories. Screw pumps for wells can be designed to operate at different well depths. There are two main types of device:

Standard, designed for use under normal conditions.
Designed for operation at great depths.

Representatives of the standard group are designed to work at well depths of up to 25 meters. Such pumps are installed with low productivity; well drilling can be carried out in country and suburban areas. In addition, equipment with different performance indicators is installed, while the pressure remains unchanged regardless of the composition of the water and many other points.

If necessary, you can purchase and install a deep-type device.

The key feature is the presence of an elongated screw, thereby expanding the scope of the device.

The key points are the following:

The device has increased performance.
Can be installed in artesian wells.
Long service life is ensured through the use of wear-resistant materials.

A significant increase in performance determines an increase in price. That is why their installation is carried out when it is necessary to ensure increased productivity.

Models that belong to the middle price category have become quite widespread. They have the following characteristics:

When choosing, attention is always paid to performance. In most cases, it varies from 1500 to 2000 l/hour. This is sufficient for most installations.
Another important parameter is the indicator of the generated pressure. It varies from 40 to 60 meters. This parameter allows you to operate the device in suburban areas.
The temperature of the transported liquid can vary in the range from 5 to 50 degrees Celsius. At low temperatures, the liquid crystallizes, causing wear and deformation of the structure.
When choosing, attention is also paid to what the maximum particle size is. In most cases, it varies from 2 to 2.5 mm.
The power of the installed electric motor, which is responsible for rotating the rod, varies from 1 to 1.5 kW.

In most cases, an electric motor is installed, which is powered by a 220 V network. You can also find more powerful versions powered by a three-phase network.

In specialized stores you can find models that are designed for installation in industry. They are characterized by higher performance properties. An example is the transportation of a medium with a higher temperature.

The classification is also carried out according to the type of material used in the manufacture of the case. In most cases it is made of stainless steel, in some cases it is made of plastic. To increase the degree of sealing, gaskets made of rubber or silicone are installed.

Types of installation of screw pumps

As already mentioned in this article, vertical screw barrel pumps are one of the types of screw pumps and are similar in design and principle of operation to horizontal ones, but have a narrowly targeted application.

A standard screw pump is installed on a horizontal surface and secured to it using special supports. The barrel is installed vertically in the container. However, there are non-standard installation options: vertical for a conventional screw pump and horizontal for a barrel screw pump. In this case, the direction of flow of the product through the pump changes, that is, the discharge pipe becomes the place where the liquid enters, and the suction pipe becomes the discharge pipe. Replacing the horizontal installation of a screw pump with a vertical one is usually due to the consumer’s desire to save production space or when it is simply limited. This once again confirms the variability of this type of pump.

Features of operation of screw pumps

The screw pumps under consideration are characterized by a fairly large number of operational features that must be taken into account. An example is the following:

Such pumping equipment is easy to maintain and repair. An example is that shaft bearings are often dismantled even in the field. Oil seals, which often fail, can be replaced without the use of special equipment. The main part can be reached using ordinary plumbing tools.
In most cases, the housing is made in such a way that the pipes are positioned along the central axis. There is a version on sale that has nozzles located at an angle of 90 degrees with respect to the central axis. Some models are equipped with special pipes that eliminate the possibility of the formation of silt deposits. Therefore, pumping liquid media does not cause a decrease in throughput.
The main part of the structure is represented by a screw shaft. It is produced using casting technology followed by high-precision machining. This moment determines that the screw pump does not cause vibration and noise during operation. It is the absence of vibration that causes a long service life.

In general, we can say that the screw pump has very attractive performance characteristics.

Accessories

As mentioned earlier, for ease of operation, horizontal screw pumps can be supplied on mobile transport trolleys. The trolley pump option is used when there is a constant or periodic need to pump liquids in different parts of one workshop or the enterprise as a whole. The trolley can, as a place for installing additional equipment, approx. frequency converter.

For barrel screw pumps, by analogy with horizontal screw pumps, a bypass valve is installed. The bypass valve is connected directly to the pump discharge pipe. During operation of the pump, the pumped liquid acquires inertial force. When the valve in the supply line is closed and the pump motor is stopped, fluid continues to flow out of the pump, creating pressure. To avoid rupture of the pressure hose, a bypass valve is installed. It is mechanically adjusted to open at a certain pressure and allows liquid, which moves by inertia, to flow back into the container.

Since barrel screw pumps are designed to operate in mobile containers, they must be constantly installed from one container to another. Since the mass of these pumps is much greater than that of barrel centrifugal pumps, their reinstallation from container to container takes a lot of effort from the operating personnel. Therefore, the motors of barrel screw pumps are produced with an additional mounting bracket. It provides easy installation and dismantling of the pump using a hoist or crane beam. If the production facility where the barrel pump is used does not have lifting mechanisms, you can purchase a special trolley for barrels with a lifting device.

How does a submersible screw pump work?

Many people decide to purchase a screw pump for a well because of the ease of maintenance and the possibility of do-it-yourself repairs. The key features are the following:

The main part is represented by a screw.
This element is connected to the rotation sources using a cardan transmission.

The installed submersible screw pump begins to work with the formation of certain cavities between the turns. At the time of operation, they are filled with water and transported.

Advantages and disadvantages

The advantages of screw (screw) pumps are much greater than the disadvantages. Let's consider what advantages this type of pump has in comparison with others:

The pump is a positive displacement pump and each rotation of the rotor is equal to a certain amount of pumped medium, so it is possible to precisely regulate the performance.
The pump is self-priming.
Since the rotating parts are directly connected to each other, and the volumetric cavities between the stator and rotor are sealed, the pump has a high efficiency.
The pump can be used in both horizontal and vertical positions.
The pump can pump liquids in different directions, as it has a reverse function.
Capable of pumping non-viscous, viscous, highly viscous and even non-Newtonian liquids.
The pumped product is not subjected to shock or compression, as a result of which its structure is not destroyed (the flow regime is close to laminar).
Various designs of the pump are possible based on the user's task (with a bypass, with a loading funnel, on a trolley, with a frequency converter).
Possibility of obtaining high performance and stable discharge pressure at different numbers of rotor revolutions.
Possibility of pumping liquids saturated with gases, since the pump is not sensitive to cavitation and hydraulic shock.
Silent operation of the mechanical part. When the pump is running, noise is heard only from the pump drive.
Low energy consumption when using an electric motor as a drive.

The disadvantages of screw pumps include their high cost, associated with the complexity of their manufacture, as well as their mass and dimensional indicators. In addition, this type of pump is not designed to operate without liquid, as this will lead to failure of the pump stator.

Design features and purpose

Modern screw pumps for water are divided into surface and submersible. The following must be taken into account:

Surface ones are installed on a special site in close proximity to the water source. In this case, the suction tube is located in the well, thereby ensuring the required working conditions. The device has a reduced operating efficiency, so it is installed only at a well depth of no more than 10 meters.
The submersible device of the screw pump is characterized by the fact that at the time of operation it is located completely in the water column. The main characteristic is an increased degree of productivity. Some models are installed at a well depth of about 50 meters or more.

Often, a screw pump is a submersible type of equipment. This moment determines that the device is completely located in the water column. In some cases, the equipment is called screw, since the main element is an Archimedean screw.

Applications of screw pumps

Screw pumps are actively used in various industries. Due to the specifics of the product being manufactured, namely high viscosity and density, these pumps are widely used in the food industry. They are used in winemaking (wine, grapes), in the dairy industry (butter, yogurt, sour cream, ice cream, cream, milk, kefir, cottage cheese, cheeses, margarine, condensed milk), in confectionery (honey, molasses, chocolate, jam, jam, jelly, mousse, cream), for various sauces and seasonings (mustard, ketchup, tomato paste, mayonnaise), etc. They are used in the cosmetics industry (shampoo, liquid soap, hair dyes, lipsticks, creams), the oil industry (petroleum, bitumen-polymer materials, diesel fuel, fuel oil, gasoline), and the chemical industry (detergents, inks, paints, glue , acids, alkalis), pulp and paper industry (flocculants, sludge, paints, paper pulps, tall oil, pulp-water slurry, dyes), as well as in the treatment of domestic and industrial wastewater (flocculants, coagulants, sludge, sludge, lime milk , sapropel).

Popular manufacturers

For installation in small-diameter wells (100-120 mm), “Aquarius” brand pumps, produced in Ukraine, are used. The equipment is characterized by a reduced cost; pumping of aggressive liquids is allowed.

Similar pumps are produced by Belarusian; Stainless steel is used for the manufacture of external elements. The advantage of Belarusian equipment is an additional sensor that turns off the power when the engine overheats.

Russian Vikhr pumps have a stainless steel body; The design provides hooks for installing a safety rope. The equipment allows immersion to a depth of up to 35 m; a 550 W motor is used to drive the auger.

The budget segment of imported equipment is occupied by products of the Chinese manufacturer Unipump. The equipment is made of stainless steel; long-term pumping of water contaminated with sand or clay deposits is allowed.

Grundfos pumps are used to supply water from depths of up to 55 m. The manufacturer offers several modifications of products that differ in body diameter and performance. The smallest pump has a housing with a diameter of 75 mm.

The design uses a block for smooth acceleration of the motor rotor and provides protection against undervoltage or overvoltage in the power circuit. The equipment is distinguished by the use of high-quality components, which increases the final cost of the product to 40-45 thousand rubles.

Varieties

Despite the similar principle of operation, screw pumps are divided into several types according to design features. Based on the design, the equipment in question is divided into three main categories. The first type is screw modifications. They are designed for pumping a significant amount of mixtures that contain aggressive chemicals and abrasives.

Auger equipment operates equally efficiently in vertical and horizontal positions. This equipment is often used for servicing wells and deep wells. Among the advantages of this category are simplicity of design and relatively low price.

Rod and vacuum versions

The design and operating principle of a rod-type screw pump allows it to be used in enterprises involved in the production and refining of oil and similar substances with high viscosity. The equipment design includes a wellhead gland, a rotary string and a surface drive unit. Among the advantages of units of this configuration is high productivity. The downside is the high cost.

A vacuum screw pump, the operating principle of which is based on the operation of a pair of rotors, is also designed for pumping liquids of varying degrees of viscosity. The moving elements rotate in different directions, due to which the treated composition first enters the area between the working chambers and the cylinder, and then is fed into the exhaust gas outlet.

It is worth noting that the operating efficiency and productivity of the equipment in question, regardless of the type, is mainly influenced by correct operation. Therefore, before purchasing a unit, you need to make sure that it corresponds to the chosen action.

Classification of screw machines

In the retail or wholesale trade network there is a wide range of screw pumps, differing from each other in the general design, individual components, equipment, materials used and technical characteristics. The latter can vary significantly, even if the units look similar or have dimensions of the same order. Based on this, the criteria for classification can be selected by weight, but most often the key is the number of working rotors: 1. Single-screw. The design uses a single-start rotor and an elastic race, the inner surface of which has a double-start screw shape. They are simpler to manufacture and assemble, relatively compact, have high efficiency and suction capacity. Operating parameters are up to 600 m3/h and 50 bar, at an ambient temperature of -40...+350°C; 2. Twin-screw. The casing of such a screw pump contains two rotors - driving and driven - with a special double-sided thread. The shafts rotate in reverse directions, providing a flow of up to 2200 m3/h and a pressure of over 100...110 bar. Most often they are used for pumping viscous, emulsion media, for example, a mixture of water and oil, its distillation products, paints and varnishes; 3. Three-screw. The cage contains three double-threaded screws. This combination allows for a flow rate of 800 m3/h and a pressure of up to 320 bar. These machines are most often used to move non-abrasive liquids, fuel oil, and technical oils. They have high durability; 4. Multiphase. These are units with one, two or three rotors, which are adapted for pumping liquid-gas mixtures with a content of the latter at 97%. They have reduced energy consumption and high resistance to abrasive particles.

The gerotor pairs themselves come in four types, providing different levels of performance and differential pressure. For example, the “S” and “L” types of cages have a cross-section of the screw channel in the shape of a rounded rectangle, and the rotors have a circle. The differences between them lie in the length of the spiral pitch (in the second case it is longer). A similar pattern is observed for pairs of types “D” and “P”. They also have differences in the pitch of the screw, but it has an oblong, oval cross-section, and the stator is triangular, rounded at the tops.

Minor cons

Among several disadvantages, the following are noted:

when working with screw pumps, it is impossible to adjust the working volume;
difficulties are observed when working with other species;
screw models have worse overall dimensions and weight;
have a high price.

What should you think about first when choosing a pump design?

How well the pump works for you depends on the following important factors:

on the type of installation of the structure and its characteristics of use;
on the flow rate of the pumped liquid;
from the pressure indicator;
depends on what substance will be pumped: we are talking about density, composition, temperature and viscosity.

Choose equipment wisely, and it will definitely serve you for a long time and with high quality, because a lot really depends on what criteria you use when choosing.