Single stage pump. Centrifugal single-stage pump for water: diagram

designed for pumping stations. In plumbing installations, general-purpose equipment is most often used. For the most part, double-sided pumps of type D are installed at the stations, and if it is necessary to supply large volumes, console devices are used.

Vertical pumps

The single-stage vertical centrifugal pump is used at buried stations, the construction of which is difficult in conditions of too close water levels. This makes it possible to reduce the cost of construction, reduce the size of the machine room, improve the quality of operating conditions for electric motors that can be moved to the first floor.

Axial pumps

Such installations are most often used with large water supplies. Sewage dynamic pumps for the most part are installed at stations of systems of removal of household waste. The water temperature is up to 80 degrees and the possible content of up to one percent of abrasive particles is provided. In sewerage systems, installations of the Gr and GrU types can also be used.

Centrifugal single stage pump and its properties

The operational properties of such pumps are determined by their main parameters: power, head, NPSH, delivery, suction lift. Important qualities of the units are the voltage of the electric motor and the speed of the wheel.

It must be understood that the parameters of axial and centrifugal pumps are variable even with continuous action impeller and will depend on the feed. In the drawings, it is customary to give characteristics for reduced wheel diameters. The characteristics of the optimal regime points correspond to the maximum efficiency. Appropriate set and delivery are acceptable indications for a pump. These characteristics are included in the designation of installations.

Operating point

The operating point is the position corresponding to the current mode of action. It does not always match acceptable indicator, but it must be close to them. single stage centrifugal pump for water always operates within the operating range, which is determined according to the allowed reduction in efficiency. Operating points should only be within these limits. The characteristics of each device are described by the manufacturer with the expectation of clean water with a temperature of twenty degrees at optimum atmospheric pressure at ocean level.

Pumps types K and KM

The centrifugal single-stage type operates with a single-sided impeller located on the edge of the pump shaft. Discharge nozzles rotate 90, 180, 270 degrees. It depends on the specific layout conditions. Bearings in mechanisms are lubricated liquid substance. Cantilever single-stage centrifugal pump can have several modifications: installation without an engine (K) and in a monoblock design (KM). After these letters, the flow and pressure are indicated on the marking.

Units with two-way supply

Single-stage horizontal pumps of class D with semi-volute inlet are available on the market. The horizontal lifting of the cast-iron body is carried out in the plane of the shaft axis. This feature makes it possible to disassemble and repair the device without the need to dismantle the pipeline. Each double-sided pump is marked with the symbol "D". After this letter, two numbers are indicated: flow and pressure.

What is a console installation?

The single stage centrifugal water pump consists of the following parts: casing volute, support, front cover, Working wheel, suction pipe, nut, shaft, stuffing box bush, ball bearing.

The principle of connecting components

The axial pressure is partially balanced by means of relief holes. Also, the wheel is supplied with an axial seal on the back side. A tube with a nozzle is connected to the discharge chamber. The second ball bearing is installed to fix the rotor and better perception unbalanced axial force. A hydraulic seal is provided on the pump seals.

Such installations have a capacity of 28 to 100 liters per second with a head of 12 to 98 meters. High-performance single-stage pumps mostly have the possibility of double-sided supply. At normal axial pressure, a good dual-flow impeller has fairly high cavitation rates.

Housing and seals

In pumps designed for pumping clean liquids with temperatures up to 80 degrees, a cast-iron casing with horizontal splits along the shaft axis is provided. Interchangeable O-rings made from cast iron. The pump shaft is made of steel and rotates on one thrust and radial bearings with ring lubrication.

The glands are equipped with which is carried out using tubes that bring fluid from the spiral chambers. Such a single-stage cantilever centrifugal pump has a capacity of 30 to 1800 liters per second and a head of 10 to 100 meters.

Vertical shaft units

There are two brands of single-stage devices for clean water: 20 HB and 28 HB. They are designed for installation in buried stations. In this installation, the heel of the electric motor perceives axial forces. On the stuffing box of the pump there is a hydraulic seal with a soft packing. HB type units are connected directly to electric motors or by means of rigid seam couplings through an intermediate shaft. Single-stage vertical centrifugal pump has a capacity of 3240 to 10 800 cubic meters per hour and pressure from 29 to 40 meters.

Features of sewage pumps

The centrifugal single stage pump is used for pumping sewage, sewage and sludge. One of the main reasons pumps stop during use is clogging. To prevent debris from entering the mechanisms, special gratings are provided. Their installation necessitates a change in the form of the installation.

Such pumps are sealed with steel rings with a sharp edge that cuts the fibers that enter the seals. The units are equipped with covers that provide easy access for cleaning the suction part of the impeller. The number of paddles is kept to a minimum to reduce the possibility of clogging. The passages between them thus increase. Quite often, the number of blades is reduced to two.

Cantilever Single Stage Centrifugal Pump sewer type Made from non-corrosive materials. Its body has several connectors necessary for partial disassembly during the cleaning process. The leading edges of the blades are rounded very strongly. Due to this, fibrous bodies will not get stuck on them.

Pumps of the NF, NFuV and FV brands. Open and Diagonal Devices

The following unit sizes are provided: 2NF, 4NF, 6NF, 8NF. Their productivity ranges from 36 to 864 cubic liters per hour with a pressure of 6.5 to 50 meters. Similar settings can be used sewer pumps with an open impeller with two thick blades. In such devices, all fibers are cut by the sharp edge of the blade.

To work with sewage quite often, a single-stage centrifugal pump of a diagonal type is used. The impeller in these units, as well as in models of the FV and NFUV brands, is equipped with two blades. Their productivity varies from 43 to 150 cubic meters per hour, and the head reaches 63 m.

Suckers

Suction dredgers are used when pumping mixtures of loosened mass of soil and liquid through pipes to the required distance. Today, the market produces pumps with a transportation range of up to 5 km and a capacity of 40 to 1200 cubic meters per hour. With the help of dredgers, it is possible to develop excavations up to 15 m deep below the water horizon. These installations have a number of features due to the high concentration of large particles in the pumped water mass. For this reason, a wear-resistant wheel made of manganese hard steel is created.

The single-stage vertical centrifugal pump is protected by armor on the inside of the casing to prevent rapid wear. To prevent the mechanism from becoming unusable so quickly, purified water is supplied through special drillings between the wheel into the left cavity and to the oil seal to flush out solid fragments from these places.

Radial blades are installed on the outer part of the working and covering disks of the wheel. They are selected so that the axial amplifier comes into balance during rotation.

Vacuum pumps

A single-stage centrifugal pump with a vacuum device is created in two main versions: dry, sucking only gas, and wet, also working with liquid. The difference can only be determined by distribution nodes. At wet pumps dead space dimensions are much larger, so they have a higher ultimate pressure compared to dry ones. The highest rotational speed during operation is achieved by samples with vertical arrangement shaft.

Non-self-priming device

The non-self-priming single-stage centrifugal pump is used for pumping milk or other viscous food products, the temperature of which does not exceed 90 degrees. The working blades of the wheel are closed and every part of such an installation that comes into contact with the liquid is made of good of stainless steel and other materials allowed for use in the food industry. The engine is protected from water ingress by a special facing casing.

Conclusion

The centrifugal single-stage pump, the scheme of which is described in this article, can be used in the most various fields. The method of application and the materials pumped will affect the performance of such units, as well as the material from which the parts are made and the way they are placed in the mechanisms. The pumps can be used for the distillation of clean water, a mixture of liquid and dirt, sewage and food mass of various viscosities.

Mechanisms designed for pumping liquids used for food are made of quality materials, the use of which is allowed by the Ministry of Health. Pumps that are used to remove sewage liquids containing large fibers are designed in such a way that large parts are dissected and do not interfere with the normal operation of the mechanisms.

Horizontal design is too general a parameter so that the pumps corresponding to it various types could be characterized by a set common properties and select a row common areas applications. Within the same type of pump, the execution can influence both the design and the functions performed by the machine to varying degrees.

Below we will consider the most common types of pumping equipment, specific representatives of which may have a horizontal design.

Centrifugal pumps

As one of the most widely used types, centrifugal pumps are found in both horizontal and vertical designs, with a wide variety of specific varieties. Centrifugal pumps are often used to pump large volumes of liquids into various industries and enterprises, where, as a rule, the problem free space is not critical. For this reason, the types of horizontal centrifugal pumps are numerous and varied.

Horizontal placement allows the pump to be easily connected to the drive by connecting the motor shaft and the pump shaft with a coupling. In most cases, the pump and motor are mounted immediately on a common frame and represent a separate technological unit. Also, several pumps and drives combined into a single pump unit can be located on one frame.

Piston pumps

Piston pumps are quite compact compared to other types. In addition, the principle of their operation does not impose strict requirements on the position of the working chambers and pistons. Moreover, the design of the pump most often allows you to move the pump from a horizontal to a vertical position without disrupting its operation, leaving only the problem of fastening. Piston and plunger pumps are often used in high pressure installations (including mobile ones), in which they are mounted horizontally with a drive on the same platform or frame.

Piston pumps that operate at a high speed or create a significant head are usually made in a horizontal design, since in this case it is easier to ensure the stability and rigidity of the pump and drive mounting. The reciprocating nature of the operation of piston pumps causes various kinds of pulsating loads on the parts and connections of the unit, which can adversely affect the pump up to failure.

Screw pumps

Used for pumping viscous media, screw pumps are widely used in the most different areas industry. Typically, screw pumps are mounted on a frame with a drive in a horizontal position, which facilitates both the installation itself and access to the pump for further maintenance, as well as the connection of the input shaft to the output shaft of the motor. Different in design, horizontal screw pumps can have branch pipes, the axes of which will lie in the same plane or in perpendicular planes.

Manufacturing screw pump in a vertical version is not justified if the space available for its placement is not a limiting factor, since in such a case it becomes necessary to solve the problems associated with mounting the pump, which usually has a significant length in comparison with other overall dimensions.

To perform some tasks, the horizontal location of the screw pump is mandatory if the inlet pipe has the form of a receiving hopper, from the bottom of which the pumped medium is captured by the screw and forced into the outlet pipe. This loading option can be found in the food industry, processes using or obtaining plastics, etc.

Properties of horizontal pumps:

Welded steel skid:
Modular design

Engines

Combustion chamber body:
Standard and Reinforced
Available power

Intake manifold:
316 Stainless Steel Construction Multistage Centrifugal Pump

Flanged pump discharge

Double flexible motor coupling

customizable in operating conditions pump base frame

Technical data of horizontal pumps

Capacity from 11 to 3240 m³/h
Head from 10 m to 2000 m

Scope of horizontal pumps

mining industry
Injection of fluid in the field
Pipelines
Water pumping
Descaling in steel mills

The most common type of water pumps is centrifugal units, depending on the design features, it is classified into two groups: single-stage and multi-stage pumps.

In this article we will talk about their differences, device, principle of operation, advantages and disadvantages. The product range of the leading manufacturers of centrifugal pumps, Grundfos and Lowara, will also be considered.

1 Principle of operation and design differences

Centrifugal pump - equipment that pumps a working fluid due to centrifugal force, which is created as a result of the rotation of the bladed drum. Such units have a metal or steel case, inside which there is an electric drive and a rotation shaft. A drum is rigidly fixed on the shaft, which can be open (consists of one disk and side blades) or closed (two disks, between which the blades are placed).

The blades of the drum are angled, they are directed in the opposite direction to the direction of its movement, which is necessary to ensure the most effective capture of water. On the body of the unit they have two branch pipes - suction and supply (pressure), through which the pumped liquid circulates.

When the pump housing is filled with water, the drum begins to rotate, water enters the blades and, as a result of the movement of the wheel, is thrown under pressure to the pressure pipe. As a result, a high pressure zone is created in the outlet pipe area, while a rarefaction zone is created in the central part of the drum, under the influence of which water will begin to flow through the pump suction pipe. This principle ensures a continuous supply of liquid circulation pumps any type. Unlike piston units, they do not have problems with uneven, pulsating pressure, which greatly expands the scope of such equipment.

Consider the device of a single-stage unit:

1. Housing, also referred to as a volute (the diagram shows a horizontal type of housing).
2. Impeller.
3. Working shaft seal.
4. Rotation shaft.
5. Chamber seal with oil bath.
6. Bearing support.
7. Bearing support.
8. Holes for monitoring the oil level in the chamber.

Single-stage centrifugal pumps have one impeller, while multistage pumps have two or more. At the same time, their principle of operation remains identical, only improved performance characteristics equipment - productivity (the amount of pumped water per minute) and pressure (the maximum distance that the liquid can be pumped). The head is indicated in meters, which indicates the distance of pumping in height, in order to find out the maximum length of liquid transportation, the head must be multiplied by 10.

Depending on the constructive device multistage centrifugal pump can be sectional or scroll. The sectional unit is different in that the liquid is pumped sequentially - from the first drum to the next. The maximum performance that a sectional pump can develop today is 900 m 3 / h at a head of 1900 m.

1.1 Centrifugal pump device (video)

1.2 Advantages and disadvantages of centrifugal units

The widespread use of pumping equipment operating on the principle of centrifugal force is explained by the presence of a number of operational advantages in this technique, which include:

• compact dimensions and low weight due to the direct connection of the rotation shaft with the engine, the design does not imply the presence of any transmission mechanisms;
• reliability and durability, no need for regular maintenance;
• smooth supply of the working medium, zero risk of hydraulic shocks;
• the ability to work with contaminated liquids containing mechanical particles, which is achieved due to the absence of valves in the design;
• affordable cost due to the simplicity of designs.

The only drawback of these units is the relatively low efficiency when operating in low productivity mode. This problem becomes especially critical when it is necessary to pump a small amount of water under high pressure.

Also, the impossibility of quickly starting the equipment can be considered as a disadvantage, since the pump housing must be filled with water before pumping. In general, for productive work, centrifugal pumps are the best choice.

2 Equipment classification

Both multi-stage and single-stage units, depending on the position of the axis of the impellers in space, are classified into:

• horizontal;
• vertical.

In a horizontal configuration, as a rule, large-sized industrial units are made for stationary installation, and horizontal units are also used in automatic water supply pumping stations, in which they are associated with a hydraulic accumulator housing. Vertical equipment is more common in the field of domestic use, in such a case all types of borehole pumps, drainage and fecal units are made.

Also, one of the main factors in the classification of centrifugal equipment is its division into types depending on the position of the unit body relative to the pumped liquid, according to which pumps are surface and submersible.

Structurally, submersible equipment can provide pumping up to 16 m3 of liquid per hour at a pressure of up to 200 meters. Almost all borehole pumps submersible, since they can raise water from a great depth (40 meters or more), while surface units, in principle, cannot suck water from a depth of more than 10 meters.

Among the differences, we also highlight the fact that submersible installations much quieter than surface ones, which is important when installing a pumping station inside a dwelling. However surface pump easier to maintain and repair, since it does not have a completely sealed housing.

Consider the remaining classes of centrifugal equipment:

• depending on the developed supply pressure: up to 0.2 MPa - low, up to 0.6 MPa - medium and over 0.6 MPa - high pressure;
• according to the coefficient of speed - quiet, normal and high-speed;
• on functional purpose- water, fire, oil, drainage, fecal;
• according to the type of connection of the wheel with the engine - cantilever, drive, coupling.

The efficiency of such units directly depends on their speed, wheel speed and design. So, compact single-stage pumps have an efficiency of 0.6-0.7, large-sized ones - 0.9-0.92.

2.1 Manufacturers and popular models

The world's leading manufacturers of centrifugal equipment are Lowara (Italy) and Grundfos (Denmark). Both manufacturers supply the market with units for both household and industrial operation. The assortment of Italians includes five lines of pumping equipment:

While the Italian company specializes in multi-stage technology, the leading position in the segment of single-stage units is occupied by Grundos pumps. In the company's assortment, horizontal units are represented by the JP series (which includes the popular single-stage Grundfos pump JP 5), vertical - series TP (standard equipment) and TPD (in-line pumps).

Single stage centrifugal pumps

Single-stage centrifugal pump is a kind of centrifugal pump, which is widely used for pumping water, highly reactive liquids, suspensions, emulsions in many industries. This type of pump has one stage, that is, one impeller. A single-stage pump can have one or two-way fluid supply to the impeller. Due to the rotation of the impeller, the liquid entering the pump leaves it at an increased speed and increased pressure. Structurally, they are divided into horizontal and vertical single-stage centrifugal pumps. The latter have a vertical working position and create high blood pressure outlet compared to horizontal ones.
Single-stage centrifugal pumps are used for urban water supply, industrial and agricultural water management, field irrigation, pumping oil products, aviation fuel, etc.

CN MAG-M

Max. pressure 16 bar for standard version and 150 bar for HP version (higher values ​​possible on request). They are used for pumping (explosive) dangerous, toxic media interacting with the atmosphere. No glands, external flushing systems, seals or valves, but ensures complete tightness even in heavy duty applications. impellers closed type, statically and dynamically balanced, end suction. External ball bearings (L10).

MZ series pumps with magnetic drive are made of thermoplastic. Capable of maintaining a constant head over a wide range of pumping speeds. For use in chemical industry. Available limited opportunity dry work.

NZ series single stage end suction horizontal thermoplastic pump is economical solution for pumping a wide range of chemicals. Mechanical seals, single (TB/RA) and double (DROTT).

Cast horizontal single-stage end suction and side discharge pumps with volute casing. Production material - thermoplastic. For pumping low density chemicals. Excellent for polishing, electroplating, filtering, cleaning, and general chemical industrial applications.

NJL

NJL series pumps are manufactured from PFA/FEP. End suction. They are an excellent alternative to expensive pumps made of heat-resistant alloys for corrosive and toxic media (including acids). Complies with ISO 2858 / ISO 5199 / EN 22858 standards. Single and double mechanical seals. Roller bearings.

NJK

Cast pumps of the NJK series - horizontal single-stage centrifugal end-suction pumps. They are an excellent alternative to expensive high temperature alloy pumps for handling hazardous, toxic and corrosive media. Dimensions and design according to ISO 2858 / ISO 5199 / EN 22858 standards. Single (TB/RA) and double (DROTT) mechanical seals, oil lubricated bearings.

NJRP

NJRP series cast horizontal end suction pumps are available with single (TB/RA) or double (DROTT) mechanical seals. The flow part is designed to withstand high loads and flange pressure. The NJRP series pumps are an excellent alternative to expensive pumps for handling hazardous, corrosive, toxic media. Conform to ISO 2858 / ISO 5199 / EN 22858 standards.

Centrifugal pumps are widely used both in everyday life and in industry. Depending on the design, they are referred to as multistage or single-stage pumps. Pumping equipment belonging to each of these categories not only has a special internal organization, but also differs in specific technical characteristics and, accordingly, areas of application.

Design differences

The centrifugal pump, which becomes clear from its name, is a device that pumps liquid media due to the centrifugal force acting on them. The main working body of pumping equipment of this type, which ensures the formation of such a force, is a wheel (or drum), on the outer cylindrical surface of which special blades are fixed.

The casing of the pumps of this type can be made of cast iron or steel alloy. Inside such a housing are placed a drive motor and a rotation shaft connected to it, on which a wheel with blades is fixed. According to its design, the pump impeller can be open or closed. Open impellers consist of one disk, on outer surface which the blades are fixed, closed - from two disks interconnected by working blades.

The blades are located at a certain angle, their bend is directed in the direction opposite to the direction of rotation of the impeller. This arrangement of blades provides more efficient work pumping equipment. The suction of the pumped liquid medium into the internal chamber of the pump, as well as its ejection into the pressure line, is carried out through the nozzles.

The principle by which both single-stage devices and multi-stage pumps work is as follows.

• The liquid inside the pump before starting it is captured by the blades during the rotation of the impeller and begins to move along with them.
• Under the influence of centrifugal force, the liquid is thrown to the walls of the inner chamber, due to which a high pressure is created near them.
• When moving through the area of ​​the discharge pipe, the liquid under high pressure is pushed into it.
• When the liquid pumped by the pump is thrown back to the walls of the working chamber, a rarefaction of air is created in the central part of the latter, which contributes to the suction of the liquid medium through the inlet pipe.

Due to the above principle of operation in pumps of both single-stage and multi-stage types, the process of suction and expulsion of the pumped liquid is ensured during the rotation of the impeller. The scope of application of pumping equipment of this type is significantly expanded by the fact that, unlike piston devices, it does not create pulsations of fluid pressure in the pipeline system it serves.

As mentioned above, single-stage and multi-stage centrifugal pumps have design features, which determine the differences in their technical specifications. So, the main structural elements of a single-stage pump are:

1. the body, which is often called the "snail";
2. impeller with blades;
3. shaft sealing elements;
4. a shaft connected to a drive motor and providing rotation of the impeller;
5. sealing elements of the chamber with an oil bath;
6. support for the bearing assembly;
7. bearing support;
8. a hole through which the oil level in the chamber is controlled.

Single stage centrifugal pump, unlike multistage models equipped with one impeller. A centrifugal multistage pump can be equipped with two or more impellers with blades, which can significantly increase the efficiency of such equipment.

Due to the presence of several impellers, centrifugal multi-stage devices, when compared with single-stage ones, have certain advantages.

• Via multistage pumps it is possible to pump liquid with a higher productivity, which characterizes the amount of liquid medium that the hydraulic machine passes through itself per unit time.
• Multistage pumps are capable of generating a fluid flow with higher head values, measured in meters of water column. In fact, the pressure of the liquid, which is created by electric pumps of a multistage type, is the sum of the pressures created by each of its stages. This quality of multistage hydraulic machines allows to achieve a higher fluid pressure in the pipeline systems they serve and move it through them over longer distances and greater heights.

A multistage centrifugal pump, depending on its design, can be sectional or scroll. In sectional-type devices, the liquid medium in the process of pumping moves sequentially from the first section of the pump to the last, while the pressure of the liquid also increases sequentially. Modern models multistage pumps of the sectional type are capable of providing the capacity of the liquid pumping process, the value of which reaches 900 m 3, while the pressure of the working medium created by such devices can reach up to 1900 meters of water column.

Advantages and disadvantages of centrifugal pumps

Both multistage and single-stage pumps have a number of advantages that make these devices so popular among consumers. The advantages of the considered hydraulic machines include:

1. compact dimensions and low weight (since the working shaft of the pumping equipment is directly connected to the drive motor, which eliminates the need for additional transmission mechanisms);
2. high reliability and long life service life, no need for regular Maintenance;
3. minimizing the risk of pressure surges (the liquid medium pumped by pumps of this type is supplied to the pressure line in a smooth mode);
4. lack of valve elements (this makes it possible to pump contaminated liquid media containing insoluble solids in their composition);
5. simplicity of design (which is why any multi-stage or single-stage pump is affordable).

Among the disadvantages of single- and multi-stage pumps are:

• rather low efficiency when operating in low productivity mode (this becomes a problem when it is required to pump a small volume of liquid medium under high pressure);
• the impossibility of a quick start (in order for such devices to start working, their working chamber must first be filled with liquid).

Grounds for classification

Centrifugal pumps (both multi-stage and single-stage) are divided into various categories according to a number of their parameters and design options. So, depending on the spatial position of the axis of the working shaft, they can be one of the following types:

• horizontal centrifugal pumps;
• devices with a vertical arrangement of the working axis.

A centrifugal horizontal pump, the axis of rotation of the shaft and the impeller of which are located strictly in a horizontal plane, is, as a rule, a large-sized installation used for industrial purposes. Centrifugal horizontal pumps are used to equip pumping stations that ensure the operation of autonomous water supply systems, in which such devices are used in conjunction with a hydraulic accumulator. Thus, a horizontal pump requires more space for your installation.

Centrifugal pumps with a vertical shaft axis and impeller are more common in the household sector. In such a design, it can be represented as a surface multistage pump used to service an autonomous water supply system, as well as a drainage or fecal pump.

Another criterion by which different categories are distinguished among single- and multi-stage pumps is the location of such equipment in relation to the liquid medium being pumped. So, depending on this parameter, pumps can be surface (or ground), submersible and semi-submersible. Surface devices, which can be a vertical multi-stage and single-stage or horizontal multi-stage and single-stage pump, are located on the surface of the earth, outside the well, but close to it.

Place such equipment, reliably protected from moisture, in a pit, on a specially prepared site or in a separate room. One of the most significant drawbacks of this type of pumping equipment is that it makes a lot of noise during operation. It should also be borne in mind that surface centrifugal pumps can only be selected if the depth of the well from which it is planned to pump water with their help does not exceed ten meters.

Centrifugal pumps submersible type during operation, they are completely immersed in the pumped medium. Some models of vertical submersible centrifugal pumps can even be placed in a pipe through which a liquid medium is pumped out. When using submersible pumps, water from a serviced well can be raised from a depth of 40 meters or more. Submersible pumps are capable of pumping a liquid medium with a capacity of up to 16 m 3 / hour, while its pressure can reach 200 meters of water column. Submersible pumps practically do not emit noise during their work, since they are completely in a liquid medium.