Single stage centrifugal pumps. Centrifugal single-stage pump for water: diagram. Console single-stage centrifugal pump. Single-stage vertical centrifugal pump Single-stage pump

vertical pumps, design feature of which is the arrangement of the shaft corresponding to their name and impeller, are widely used both in everyday life and in various industries. Due to the vertical arrangement of the shaft, impeller and casing, this equipment does not require much space, which is one of the main reasons for its high popularity. The vertical pump, depending on the model, can be used as a stand-alone mobile device, as well as an element of a water supply or sanitation system.

Parameters and varieties

Pumps with a vertical shaft and impeller arrangement, related to centrifugal type devices, are classified according to such characteristics as:

1. head (depending on the value of this parameter, vertical pumps can be with low, medium or high head levels);
2. speed of operation (on this basis, normal, quiet or high-speed hydraulic machines are distinguished);
3. the volume of the working medium pumped over per unit of time (device performance);
4. the number of stages, which can be sections or rings of equipment;
5. the number of lines through which the pumped medium enters the device (one- or two-way devices);
6. type of liquid medium for which the pump is intended to be pumped (drainage, fecal, chemical, water and other electric pumps);
7. location of the device relative to the medium it pumps (ground models, submersible and vertical semi-submersible pumps);
8. method of connection with a drive motor (direct-drive, gear and pulley hydraulic machines).

Vertical pumps are successfully used for pumping clean, contaminated and chemically aggressive liquid media characterized by a low degree of viscosity. To the most significant advantages of hydraulic machines of this type should include:

• compactness;
• ease of use and maintenance;
• high efficiency;
• Not high level noise generated during operation.

Due to the above advantages, vertical multi-stage centrifugal pumps(as well as single-stage ones) are actively used to equip the following systems:

• autonomous water supply;
• heating;
• drainage and purification of liquid media;
• condensation;
• filtration, irrigation and melioration.

A vertical centrifugal pump that raises the liquid it pumps to a higher level by increasing its flow pressure can fall into one of the following categories:

• hydraulic machine of surface or ground type;
• semi-submersible pump;
• submersible device.

Both surface models and semi-submersible and submersible pumps are equipped with an electric motor that ensures the rotation of the impellers of such devices.

Surface pumps of the vertical type, as their name implies, are installed on the surface of the earth, in the immediate vicinity of the tank from which the liquid must be pumped out. The place for installation of such equipment can be a pit or a specially prepared platform that does not come into contact with the surface of the pumped liquid medium. The vertical semi-submersible pump, which also follows from its name, is only partially lowered into the pumped liquid medium, while the drive motor remains above the liquid surface.

The housing of submersible pumps is completely in the thickness of the pumped liquid medium during their operation. If a vertical semi-submersible pump cannot be installed in wells whose shaft is characterized by a curved shape, then a submersible type device has this capability.

It should be borne in mind that vertical type electric pumps cannot be started until the inside of their housing is filled with liquid. If this requirement is neglected, the pump will run at idle, which can lead to its overheating and, accordingly, premature failure.

Higher power is characterized by multistage centrifugal pumps of vertical type, which are able to greatly increase the pressure of the flow of the pumped liquid medium, which cannot be said about single-stage models. At the same time, the power and Efficiency of multistage vertical-type pumps, the higher, the more sections there are in the design of such devices. Each of the sections, connected to each other in series, contributes to the increase in the kinetic energy of the flow of the pumped liquid medium.

Operating principle

The main structural element of a vertical type centrifugal pump is an impeller equipped with blades. In vertical multistage pumps, there are several such wheels mounted on the shaft, which makes it possible to increase the efficiency of using this equipment. The impellers of these centrifugal electric pumps are two disks mounted on a vertical shaft, which are located at a certain distance from each other and are interconnected by blades that bend in the direction opposite to the direction of rotation of the wheel itself.

The principle by which a vertical centrifugal pump works is as follows:

1. When the wheel rotates in the temporary working chamber formed by two adjacent blades, an air rarefaction is created, which contributes to the absorption of liquid into it through the inlet pipe.
2. After the liquid enters the temporary working chamber and begins to rotate along with the blades moving it, a centrifugal force begins to act on it, pressing it against the walls of the inner chamber.
3. When it enters the outlet pipe area, the liquid, already under pressure due to the centrifugal forces acting on it, is pushed into the pressure line.

When the impeller of a centrifugal electric pump rotates with blades fixed on it, the suction of the pumped liquid and its ejection into the pressure line occurs in a continuous mode. Thus, for one revolution of the wheel, several cycles of suction and expulsion of the pumped liquid medium occur.

The shaft of the electric pump, on which its impeller is fixed, is placed in bearing assemblies to ensure ease and accuracy of rotation, and sealing elements of the stuffing box type are installed between the moving and stationary parts of the device.

Some models of vertical submersible pumps can be installed even in pipelines of the appropriate diameter, which can significantly increase the efficiency of pumping liquid media. The suction and discharge pipes of such models are located on the same axis.

Multistage vertical type pumps

In multistage centrifugal vertical pumps, the pumped liquid passes through all sections of the device in succession before entering the discharge pipe, which makes it possible to significantly increase the pressure of the working medium at the outlet. Depending on the model, pumps of this type may contain in their design different quantity impellers (from 2 to 10), which are fixed on one shaft, but are located in separate modules each.

The modules of a multistage vertical pump are housed in a single casing, which is installed between the suction and pressure chambers of the device. All elements of the housing of a multistage electric pump, the branch pipes of which are located in the same horizontal plane, are pulled together with studs, and the joints between them are sealed with sealing elements.

As mentioned above, multistage centrifugal pumps, due to their design features, can significantly increase the head of the pumped liquid medium at the outlet. The head of the fluid flow created multistage pump, is the sum of the pressure values ​​formed by each of its stages.

Selection and maintenance rules

Significantly extending the service life of centrifugal pumps, as well as ensuring their trouble-free operation, allows compliance with simple rules for their use and Maintenance. To minimize the impact external factors capable of putting centrifugal pumps out of action, such installations should be retrofitted next to additional elements. These elements are, in particular:

• strainer and valves that will protect the pump from getting into it inner part solid inclusions contained in the composition of the pumped liquid medium;
• check valve, which does not allow the pumped liquid to go back into the well, that is, it excludes the operation of the pump idle and, accordingly, overheating of the device and its failure;
• a pressure gauge installed on the pipe through which the liquid medium is sucked in by the pump (the presence of a pressure gauge will make it possible to control the pressure of the liquid in the inlet pipe and thereby prevent the occurrence of cavitation processes);
• a pressure gauge designed to control the pressure level inside the pump itself (the presence of such a device will prevent the occurrence of water hammer).

Efficiency pipeline system, which is served by a centrifugal pump, is largely determined by how correctly such a device is chosen. Choosing both surface, submersible and semi-submersible vertical pumping devices, you should focus on the following parameters:

• power consumed by the drive motor;
• performance;
• the pressure of the water jet, which the pump is able to create;
• body dimensions;
• materials for the manufacture of parts that will come into contact with the pumped medium.

This article provides descriptions of pump designs used in water supply and sewerage systems, as well as in the main industries and utilities.

Axial pumps. Axial are called vane pumps, in which the liquid moves through the impeller in the direction of its axis. Main specifications axial pumps are specified in GOST 9366-80 “Axial pumps. Are common specifications". According to this GOST, axial pumps are manufactured in two types: with rigidly fixed impeller blades - rigid-blade pumps (type O) and with rotary impeller blades - rotary-vane pumps (type OP). The possibility of changing the angle of installation of the blades in OP-type pumps allows you to adjust the flow and pressure of the pump in a much wider range than in O-type pumps with rigidly fixed impeller blades. At the same time, the high efficiency of the OP-type pump is maintained.

The impeller of an axial pump consists of a streamlined sleeve on which the blades are mounted. The bushings and vanes of the axial flow pump are cast iron or steel in the basic version, and bronze in the marine version. Liquid enters the pump through the inlet pipe. In the inlet nozzles of some types of pumps there are guide vanes in the form of fixed streamlined blades. Directly behind the impeller (in the direction of the liquid) there is a straightening apparatus to eliminate the rotational movement of the liquid.
In axial pumps of type O and OP in the basic version (Fig. 2.19), the liquid is discharged at an angle of 60 ° to the vertical. In small-sized axial pumps, the liquid is discharged at an angle of 90 °. The shaft of axial pumps of the OP type is hollow, a rod of the blade turning mechanism passes inside it. The blade turning mechanism can have a manual, electric or hydraulic drive. blade settings can only be changed when the pump is not running.The design of the impeller of an axial pump predetermines the features of its operation: such pumps are designed to supply high fluid flow rates (up to 140 thousand m3 / h) at relatively low heads (4-20 m). determines another feature of axial pumps - in most cases they are designed to work under the bay.Therefore, when designing pumping units, axial pumps are installed so that the impeller is located below the water level in the receiving chamber.
Axial pumps are characterized by simple design and compactness, less weight compared to centrifugal pumps, and the ability to supply contaminated liquids. The compactness of the design is especially valuable when supplying high fluid flow rates, as it can significantly reduce the size of the pumping station. Axial pumps are used in irrigation installations and pumping stations of the first lift of water supply systems, as well as for pumping sewage and activated sludge at sewage treatment plants.
Pumps for sewage liquids (faecal) and soil pumps. Fecal pumps are designed for pumping Wastewater, silts and liquids contaminated with mechanical impurities in suspension. Therefore, such pumps must have sufficiently large passage channels to ensure uninterrupted operation. For this purpose, the impellers of fecal pumps are made with a small number (2-4) of streamlined blades. In addition, special hatches are arranged in the housing for inspection and cleaning of pumps.
The main parameters of centrifugal fecal pumps produced so far are specified in GOST 11379-73 “Centrifugal fecal pumps. Main parameters". According to this GOST, the production of fecal pumps of four main types is provided: horizontal type FG, vertical type FV, one-stage and two-stage.

Rice. 2.21. Vertical fecal pump
/ - pump housing; 2 - base plate; 3—electric motor

A horizontal fecal single-stage cantilever pump with an axial liquid supply is shown in fig. 2.20. The pump support is made in the form of a bracket, to the flange of which a simplified housing with suction and discharge pipes is attached. The suction pipe is equipped with a cleaning hatch. The second hatch for cleaning is arranged in the upper part of the pump casing.

The discharge port is usually vertical and can be rotated 90° to either side if required. The pump shaft rotates in rolling bearings, and for large pumps - in plain bearings. The shaft seal is a gland packing. For cooling and flushing the stuffing box seal, as well as to create a hydraulic seal during pump operation, the stuffing box is supplied with industrial water under pressure 0.03-0.05 MPa (0.3-0.5 kgf/cm2) higher than the pressure in the pump discharge pipe.
Vertical fecal pumps are widely used. vertical pumping units with a small feed, they are structurally solved in the form of a block with an electric motor (Fig. 2.21). The pump shaft has top and bottom bearings. In the upper support, fixed on the plate, there is a heel that perceives the axial force of the rotating parts of the pump. The lower support is located in the pump and consists of two bearings - a radial ball bearing and a textolite thrust bearing. The pump casing is connected to the base plate by means of a pipe. The pump shaft passes inside the pipe. To lubricate the textolite bearing, clean (technical) water must be supplied to it.
Large vertical fecal pumps are produced with an axial supply. The pump housing is made with a connector in a horizontal plane (Fig. 2.22). As can be seen from the figure, the pump and motor are mounted on separate foundations. Axial forces and load from the action of the weight of the rotating parts in such pumps are perceived by the heel of the electric motor, which is in an oil bath.
On January 1, 1983, a new GOST was introduced for pumps for waste liquids - GOST 11379-80E “Dynamic pumps for waste liquids. General technical conditions". According to this GOST, pumps of the SD-centrifugal and SDS-free-vortex types should be manufactured. SD pumps must be manufactured in horizontal and vertical versions, as well as semi-submersible. This series of pumps must provide a supply from 7 to 10800 m3 / h with heads from 5.5 to 10 m when pumping a liquid containing no more than 1% of abrasive particles up to 5 yul. The main technical characteristics of SD pumps (delivery, pressure) are close to those of type F fecal pumps.
In the designations of wastewater pumps, the first letters indicate the type of pump, the first group of numbers - flow, m3 / h, the second group of numbers - head, m; followed by the designation climatic design and GOST number. For example, a horizontal pump type SD with a flow rate of 100 m3 / h and a head of 40 m, climatic version U4 (according to GOST 15150-69) is designated as follows: SD 100 / 40-U4-GOST 11379-80E. A comparison of the designations of pumps manufactured in accordance with GOST 11379-73 and 11379-80E is given in Table. 2.3.
Behind Lately in our country and abroad, to simplify the operation of pumps for pumping wastewater and other liquids containing large suspended and floating inclusions, a number of new types of pumps are being developed.

Table 2.3

Centrifugal fecal pumps are made with wheels equipped with devices (knives) for grinding large inclusions.
Such a pump, simultaneously with pumping liquid, performs the function of a crusher, that is, it is a crusher pump. The use of such pumps simplifies the operation of pumping units. This primarily applies to automated pumping stations, which eliminate or significantly reduce the need to operate crushers and devices for removing solids trapped on grates. In our country, such a pump was developed by NIKTI MKH of the Ukrainian SSR (Kyiv).

For pumping wastewater containing inclusions large sizes, use free-vortex pumps (SVN), which, according to the principle of operation, belong to friction vane pumps. These pumps differ from centrifugal ones in that the open impeller is located in the pocket of the rear wall of the pump housing (Fig. 2.23). In this case, a chamber is formed between the end face of the wheel, free from rotating parts. The width of this chamber is equal to the diameter of the discharge pipe at the level of the tongue of the alignment. Only a part of the total flow of liquid entering the pump passes through the impeller - the so-called circulation flow, which is 15-25% of the pump flow. The rest of the fluid entering the pump, the energy is transferred by vortex energy exchange with the circulation flow. A wide flow cavity, free from moving parts, and an open impeller contribute to the fact that the pump is practically not clogged, and therefore, labor costs for its operation are significantly reduced. However, the efficiency of free-vortex pumps is lower than that of centrifugal pumps, and is 45-55%. Currently, the industry produces a free-vortex pump FGS 81/31 with a nominal flow of 81 m3 / s and a submersible centrifugal monoblock fecal electric pump of the TsMF 160-10-U5 brand with a free-vortex type impeller.
For pumping pulps, as well as industrial wastewater of some types with a large amount of heavy mechanical impurities, including abrasive ones (sand, scale, slag, etc.), soil and sand pumps are used.
Soil pumps type Gr, single-stage cantilever type with a four-blade impeller of one-way entry are manufactured in accordance with GOST 9075-75.
The casings of such pumps have a connector in the vertical plane. These pumps are designed for pumping slurries with a density up to 1.3 kg/l.
The main parameters of sand centrifugal pumps are established by GOST 8388-77 “Centrifugal sand pumps. Types and basic parameters. Currently, the industry produces sand pumps of the Ps type with a flow rate of 50 to 200 m3/h for pumping pulp with a density of up to 2-3 kg/l (depending on the brand of the pump). The design of the sand pump type Pr is shown in fig. 2.24. As can be seen from the figure, the pump housing, inlet and outlet pipes are rubber-coated, which prevents rapid wear of the pump.
It is necessary to supply clean water at a pressure equal to 0.8-1 of the pump operating pressure to the stuffing box seals of Pr type pumps (as well as Gr type pumps).

Recently, submersible sewage electric pumps of small power have become widespread. A series of submersible electric pumps of the TsMK type has been developed and mastered (Fig. 2.25). This is a submersible monoblock unit with a built-in electric motor, sealed from the ingress of sewage into the internal cavity. The pump part is a single-stage centrifugal pump with a two-bladed impeller fixed on the cantilever part of the motor shaft. The pump outlet is spiral. The suction and discharge cavities are separated by a labyrinth seal.
The sewer electric pump is equipped with a special device for its automatic docking with the pressure pipeline without the use of conventional fasteners, which makes it possible to dismantle the pump without emptying the well (reservoir) where it is installed.
In the course of construction work for an open spillway, as well as for pumping contaminated water, including waste water, submersible monoblock centrifugal electric pumps of the GNOM type have become widespread (Fig. 2.26). According to GOST 20763-75, these pumps must be manufactured with a flow rate of 10 to 400 m3/h at heads of 10 to 40 m.

Rice. 2.25. Submersible sewer electric pump type TsMK
1 - impeller; 2 - spiral outlet; 3 - bearing shield; 4 - electric motor; 5 - cover; 6 - handle; 7 - motor cable

The impeller of the electric pump type GNOM semi open type, cast, of wear-resistant material, fixed on the motor shaft. The electric motor of special design is asynchronous with a squirrel-cage rotor. The rotor rotates in two ball bearings mounted in the top and bottom covers. Between the impeller and the lower bearing there is an oil chamber with a seal assembly located in it. The oil in the chamber is designed to lubricate and cool the friction pairs of the mechanical seals. It also serves as a hydraulic seal to prevent the penetration of the pumped liquid into the cavity of the electric motor. The presence of an oil chamber somewhat complicates the operation of GNOM-type pumps in comparison with the operation of TsMK-type pumps. The pumped liquid is sucked in by the impeller and fed into the annular gap between the electric motor and the casing. Next, the liquid enters the pressure pipe and is pumped through the rubber sleeve. Pumps of the GNOM type are capable of pumping liquid with a density of up to 1250 kg / m3 with a content of solid mechanical impurities with a maximum size of up to 5 mm up to 10% by weight.
Abroad, submersible electric pumps for pumping wastewater are widely used. The Swedish company Flygt produces a wide range of sizes of submersible sewage pumps, including large pumps with a flow rate of up to 4000 m3/h. On fig. 2.27 shows one of these pumps. Application submersible pumps for pumping wastewater can significantly reduce the size of pumping stations, and therefore reduce their cost.

Pumps for chemically active liquids. Pumps of this class are intended primarily for chemical industry. In water management systems, such pumps are used for pumping solutions of various reagents, primarily a coagulant solution. They are also used for pumping wastewater that is aggressive towards ferrous metals. industrial productions. Types and main parameters of centrifugal pumps for chemical industries specified in GOST 10168-75. Main technical requirements for such pumps are given in GOST 15110-79E. According to these GOSTs, pumps for chemical industries are manufactured in the following types:
X, AX, TX - horizontal, console on a separate rack; HB - horizontal, intersupport, single-stage and multi-stage, with single-sided entry impellers;
HD - horizontal, intersupport, with impellers of double-sided entry;
CI, AHI, THI - submersible, vertical, with supports outside the pumped liquid;
KhP, AHP - submersible, with supports in the pumped liquid.
Pumps of these types must be manufactured in the following designs: M - monoblock; P - with increased (excessive) pressure at the inlet; O - heated or cooled; C - self-priming.

For especially chemically active liquids, centrifugal single-stage pumps are made of ceramic materials And epoxy resins. The types and main parameters of such pumps are regulated by GOST 22570-77. According to this GOST, pumps must be manufactured with a flow rate of 3 to 460 m3 / h and a head of 6 to 95 m. The most common are pumps of type X, AX and GC. These pumps are manufactured on unified support legs and bearings. On fig. 2.28 shows a section of the pump X 20/31.

1 - impeller; 2 - stuffing box; 3 - protective sleeve; 4 - pump shaft; 5 - bracket

The material of the flow part of the pump is a high-silicon alloy. The protective sleeve of the shaft is made of the same material.
Previously, the designation of pumps for chemical industries included the diameter of the inlet pipe and the speed number. GOST 10168-75 contains a table for replacing obsolete pump designations. For example, the pump X 20/31 was previously designated 2X-6, and the pump AX 90/19 - 5AX-9.

Features of single-stage pumps with a horizontal and vertical shaft are determined by their purpose.

Consider single-stage pumps for various purposes:

a) for pure water of small capacity, they are cantilevered (Fig., 37), with a one-sided inlet. Such pumps are called type K pumps; they have a frame 3, which contains the bearings 7 and is attached to the foundation. The volute casing of the pump 1 is attached to the frame with a flange and can be rotated so that the discharge pipe assumes a horizontal or vertical position.

Rice. 37. Console centrifugal pump: 1- spiral outlet of the pump casing; 2- impeller; 3- body support; 4- front cover with suction pipe; 5- shaft; 6- nut; 7- ball bearing; 8- stuffing box; 9- stuffing box bushing.

The axial pressure in the pump is partially balanced by means of a relief hole, for which the wheel is provided with holes in the working disk and a second seal on the rear side of the wheel. The axial pressure relief chamber is connected by a tube to the suction port of the pump.

To perceive the unbalanced part of the axial force and fix the rotor, a second thrust ball bearing is installed. The pump stuffing box is equipped with a hydraulic seal. Such pumps are produced with a capacity of 28 to 100 l / s and a head of 12 to 98 m. High-capacity single-stage pumps are more often performed with a two-way water supply. A double-flow impeller of high performance, in comparison with a single-flow one, has significantly better cavitation performance at balanced axial pressure (Fig. 38).

These pumps are designed for pumping clean water with temperatures up to 80°C. The pump casing is cast iron, with a horizontal split along the shaft axis. O-rings cast iron, replaceable. The pump shaft is steel, on radial plain bearings with one thrust ball bearing. Plain bearing lubrication.

Stuffing boxes have a water seal, carried out by means of tubes supplying water from the spiral chamber of the pump. Such pumps are produced with capacity from 30 to 1800 l/s and head from 10 to 100 m, the highest permissible vacuum suction height Hvdop = 5m.

Single-stage pumps for clean water of the cantilever type are produced in the following ten brands: 2K-6, ZK-6 ZK-9, 4K-6, 4K-8, 4K-12, 4K-18, 8K-12, 8K-18; the numbers in front of the letter indicate the diameter of the inlet pipe in inches, the number behind the letter - the speed factor ns reduced by 10 times.

Rice. 38. single stage pump with two-sided entrance: 1- building; 2- impeller; 3- filler hole; 4- stuffing box; 5- bearing housing; 6- bushing; 7- impeller shaft.

Pumps with a double-sided inlet and a horizontal shaft have the following brands: NDn, NDv. The series of these pumps includes: 16NDn, 20NDn, 24NDn, 6NDs, 12NDs, 14NDs, 18NDs, 20NDs, 22NDs, and 4NDv, 5NDv, bNDv, 8NDv. In these designations, the number indicates the diameter of the outlet in inches, ND is a double-sided pump, n is low-pressure, s is medium-pressure, and v is high-pressure.

By design, high-capacity pumps of the 10D-6, 10D-9, 10D-13, 10D-19, 12D-in, etc. types up to 32D-19 are close to these pumps (see Appendix 1).

Single-stage pumps for clean water with a vertical shaft are available in two grades 20 HB and 28 HB and are designed for installation in buried pumping stations (Fig. 39). Axial forces are perceived by the fifth electric motor. The pump stuffing box has a soft packing with a hydraulic lock. The vertical pump type HB is connected to the electric motor directly or through an intermediate shaft by means of rigid flange couplings. Pumps of this type have a capacity of 3240 to 10800 m 3 h, with a head of 29 to 40 m.

b) Single-stage sewage (faecal) pumps are used for pumping sewage, sewage liquid and sludge. Clogging of sewage pumps is the reason for their shutdown in operational conditions. To protect the pumps from clogging of the grate, but at the same time, the design of the pump is given a special shape, since the gratings cannot protect the pump from solid and fibrous substances entering it.

Rice. 39. Single-stage centrifugal pump with a vertical shaft: 1- housing; 2- discharge pipe; 3- suction pipe; 4, 5- sealing rings; 6- impeller; 7- nut; 8- fairing; 9- bearing; 10- support; 11- bearing housing; 12- support ring; 13- hairpin; 14- pump shaft; 15- tube for unloading axial pressure; 16- glass bearing support; 17 - manometer.

In this regard, sewer pumps have a number of features:

• they are fitted with a cover allowing easy access to the suction side of the impeller for cleaning;
• pump seals are made with steel rings with a sharp cutting edge to cut the fibers that enter the seal;
• in order to reduce clogging of the wheel, the number of blades is reduced as much as possible, thereby increasing the passages between them (often the number of blades is reduced to two);
• the leading edges of the blades are strongly rounded to prevent fibrous bodies from getting stuck on them;
• the material of the pump parts is resistant to corrosion, and the housing has several connectors for partial disassembly during cleaning.

For pumping sewage liquids, pumps of the NF brand are used (Fig. 40).

Rice. 40. Sewage centrifugal pump: 1- housing; 2- impeller; 3- front cover; 4- shaft; 5- ball bearing; 6- bearing housing.

These pumps are single-stage, horizontal cantilever and are manufactured in the following sizes: Nf, 4NF, 6NF 8NS The performance of these pumps ranges from 36 to 864 m3 / h at a head of 6.5 to 50 m. In addition to NF pumps, there are sewage pumps with an open impeller type, with two thickened blades. In these pumps, the fibers that fall between the wheel and the cover are cut by the edge of the blade.

Diagonal sewer pumps are also manufactured, the impeller of which has two blades, and vertical sewage pumps of the NFuV and FV brands with a capacity of 43 to 150 m3 / h, with a head of 15 to 63 m. mixtures of water with loosened mass of soil. The soil loosened and mixed with water is sucked in by a dredger, and this mixture is pumped to the required distance through pipes.

At present, dredgers are produced in the form of single-stage cantilever pumps with a productivity on the ground from 40 to 1200 m 3 / h with a transportation range of up to 5 km. Dredgers can develop excavations 15 m deep below the water level. In dredge pumps, all the features of pumps for contaminated and sewage liquids are repeated (see features of sewage pumps), but at the same time, dredge pumps have a number of their own features associated with a high concentration and size of particles suspended in water. Therefore, the impeller of the dredger is made of wear-resistant hard manganese steel.

To protect against rapid wear, the body of the dredger is protected from the inside by armor cast from manganese steel. Penetration of abrasive particles into the seal slots of the impeller and stuffing box would cause them to wear quickly. To eliminate this, the stuffing box and the left cavity between the impeller and the housing are supplied with pure water through special drillings to flush out solid particles from these places.

Radial blades are provided on the outer surfaces of the covering and working disks of the impeller. These blades are selected so that they balance the axial force as the impeller rotates. The fixation of the rotor in the axial direction and the perception of the axial force is carried out by an angular contact ball bearing. The radial bearings of the shaft are plain bearings.

For pumping contaminated water from the pit and trenches when construction work mobile self-priming centrifugal unicycles are also used pumping units. Distinctive feature self-priming pumping units is their ability, after the casing is filled with water for the first time, to produce self-priming at each subsequent start-up of the pump.

The industry commercially produces such pumping units S-203 and S-204 with an electric motor, pumping units S-247 and S-245 with an internal combustion engine.

Rice. 41. Spiral two-stage pump.

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Console centrifugal pump: spiral outlet of the pump casing; Working wheel; body support; front cover with suction pipe; - shaft; screw; ball bearing; gland packing; - gland bushing.

All existing centrifugal pumps can be divided into the following groups: 1) according to the method of water removal: a) simple (without a guide vane);

b) turbine (with a guide vane); 2) by the number of impellers: a) single-stage; b) multistage; 3) for water supply: a) with one-way supply; b) with a two-sided supply; 4) according to the position of the shaft: a) with a horizontal shaft; b) with a vertical shaft;

When the device rotates, centrifugal force acts on the liquid located in the interblade space, as a result of which water flows out from under the working stage. This contributes to the occurrence of a vacuum directly in the center of the stage, and also to an increase in pressure at the periphery. The liquid goes through the suction pipeline and enters the pump through the nozzle. The movement of water in the suction pipeline is carried out due to the pressure difference in the central region of the wheel and the receiving basin. The liquid ejected from the impeller enters the spiral chamber, after which it moves to the pressure pipe, which is connected to the pressure pipeline. larger diameter wheels and the higher the speed, the greater the centrifugal force, and, accordingly, the pressure of the pump. An electric motor is used as a drive for the unit.

2. Multistage centrifugal pumps. Multistage pumps are designed to create high pressures. On common shaft Several impellers are rigidly fixed rotating from the engine, through which the flow moves sequentially. To direct the flow from the exit of the previous to the next wheel, sectional pumps use a guide vane, it consists of 2 systems of vanes that guide (located behind the reverse impellers. In others pump designs for this purpose have special channels or additional nozzles in the casings, which worsens the compactness. When the flow moves sequentially through the impellers, the pressure increases, at the pump outlet it is determined by the product of the pressure of one stage by the number of feet. There are horizontal and vertical. Horizontal 3 -x types of CNS

Depending on the method of fluid supply to the impellers: single-threaded; multi-threaded.

According to the method of removing liquid from the impeller: spiral (volumetric); turbine type.

By hull design: single-case type; sectional type.

By the number of impellers: single-stage; multi-stage.

In terms of speed: low, medium, high speed.

According to the drive method, the pumps are divided into: electric, steam (the drive is driven by the selection of steam from a steam turbine).

According to the location of the shaft axis: horizontal, vertical,

By type of application: mine, sewer, nutrient;

By type of pumped liquid: acid, slurry, dredgers, fecal, etc.