Pumps dry or wet rotor. Pumps for heating with a "wet" rotor

Dry rotor pumps are used to pump liquids with high pressure. They are best suited for supplying coolant and aggressive media. Unlike wet rotor pumps, in these pumps the liquid does not come into contact with the motor.

Another difference from glandless pumps is the way the pump housing/shaft is insulated. This is achieved using stuffing box or sliding mechanical seals (STU).

Standard dry rotor pumps typically use three-phase, constant speed motors. As a rule, they are regulated through an external electronic system speed control. Today, dry rotor pumps are available with a built-in electronic speed control unit, which, thanks to modern technology can be installed on motors with high output power.

The overall efficiency of pumps with a dry rotor is significantly higher than that of pumps with a wet rotor. Dry rotor pumps are divided into three main types:

In-line pumps
Pumps in which the suction and discharge pipes are on the same axis and have the same nominal bore are called in-line pumps. In-line pumps are equipped with standard flange motors with air-cooled. This type of pump is considered the most suitable for building systems requiring high power output. These pumps are installed directly on the pipeline. In this case, the pipeline is fixed with brackets or the pump is installed on a foundation or a separate bracket.

Block pumps
Block pumps are low pressure, constant speed centrifugal pumps with a standard air-cooled electric motor. Fluid enters the pump in an axial direction and exits in a radial direction. Brackets or motor supports are standard on the pumps.

Console pumps
Data centrifugal pumps have an axial inlet and a radial outlet of the liquid from the pump. The pump and motor have independent attachment points. Therefore, they are installed on a foundation slab.

Depending on the fluid and operating conditions, they can be equipped with a STU or a stuffing box seal. The nominal passage of such pumps is determined by the discharge pipe. The suction pipe has a larger conditional passage.

Shaft seal
The shaft can be sealed (as standard or as an option in the case of cantilever pumps) against the atmosphere with a CTU or gland seal. Below is a description of these two types of seals.

STU pump with a dry rotor

Sliding mechanical seals
The mechanical seal is based on two rings with carefully polished surfaces. They are pressed against each other with a spring and work together. STUs are dynamic seals and are used to seal a shaft rotating in a liquid at high operating pressures. STU consists of two polished wear rings (eg silicone or graphite), which are pressed against each other by axial forces.

One ring (dynamic) rotates with the shaft, while the other ring (static) is fixed in the housing. A thin film of water forms between the sliding surfaces, serving as a lubricant and cooling agent. Depending on the mode of operation of the pump, several types of friction of the mating surfaces are possible: mixed friction, boundary friction or dry friction, the latter (occurring in the absence of a lubricating film) causes immediate destruction of the surfaces.

The service life depends on the operating conditions, such as the composition and temperature of the working fluid.

Stuffing box seals
Good quality synthetic fiber yarns such as Kevlar® or Twaron®, PTFE, porous graphite yarn, synthetic mineral fiber yarn, and natural fibers such as hemp, wadding or ramie are used as materials for stuffing boxes.

The stuffing material is produced in the form of threads or compressed coils, in dry form or with special impregnation, depending on the purpose. If the material is purchased in the form of threads, you first need to form a ring and give it a shape. Then, the stuffing box ring is wrapped around the pump shaft and tightened with a ferrule.

Mounting types

Permissible mounting methods
In-line pumps are designed for horizontal and vertical installation directly on the pipeline.
Sufficient space must be left for dismantling the motor, pump elements.
When connecting the pipelines, stress and weight of the pipelines must not be transferred to the pump, and the pump must be installed on supports (if any).

Prohibited mounting methods
Mounting with the motor and terminal box pointing downwards is not permitted.
If the motor power exceeds a certain level, the manufacturer should be consulted before installing the pump in a horizontal position.

- Section of a centrifugal pump high pressure
- Characteristics of high pressure centrifugal pump

High pressure centrifugal pumps

These pumps are usually multistage. The flow rate of the pump depends on the size of the impeller and other factors. The pressure in high pressure centrifugal pumps is achieved by using several impellers installed in series. Kinetic energy is converted into pressure partly in the working, and partly in the straightening apparatus.

Due to the possibility of varying the number of stages, high-pressure centrifugal pumps develop a higher pressure compared to low-pressure single-stage centrifugal pumps.

Some pumps have up to 20 stages. Thus, they can provide heads up to 250 m. Almost all high pressure centrifugal pumps that we have described belong to the dry rotor pump family. However, in recent times manufacturers successfully equip them with wet rotor motors.

Special instructions for block pumps
Block pumps must be installed on suitable foundations or brackets.
Installation of a block pump with the motor and terminal box pointing downwards is not allowed. All other mounting methods are considered acceptable.
For details on installation methods, see the installation and operating instructions.

In several floors, the potential of an autonomous heating system is not always enough. The pressure value in it does not step over the line of 0.6 MPa. To increase the pressure and improve the water circulation process, you must either create a closed line consisting of pipes of a rather large cross section, or add a pumping unit to the equipment. Since pipes are expensive nowadays, it is better and more profitable.

Experts have been trying to cope with this task for a long time, for example, using a pump with an electric motor. But the open-contact motors available at the dawn of the last century were vulnerable when water hit them, which instantly rendered the unit inoperable.

Only in the twenties, one German mechanic managed to assemble a sealed engine. On its basis, after a while they prepared. For almost 30 years, such constructions worked regularly, taking part in heating the dwellings of Western Europe and the United States.

A clear disadvantage of the "primitive" circulating water pump was a poor stuffing box seal, the rapid wear of which manifested itself with minuscule flaws, scratches on the shaft, and the material of the stuffing box did not suffer from strength. The equipment needed sealing, the shaft needed grinding, so repairing the circulation pump was not uncommon for that time.

Later, the knee was replaced with a snail familiar to today's realities, and the centrifugal apparatus acquired modern features in appearance.

Types of circulation pumps for heating and their device

A bypass pipeline in heating is nothing more than a piece of pipe that is installed parallel to the shut-off and control valves. Its task is to switch the heating to natural circulation at the time of a power outage and equipment.

The devices at this node are installed according to the movement of circulating water:

• filter,
• check valve,
• flange circulation pump.

The introduction of devices into the riser is done through shut-off valves. During the transition of the system to natural circulation, if the devices fail, the valves on the bypass are closed, but the shut-off valve under it opens.

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For the successful operation of the “wet” water pump, and so that air does not accumulate in the system, the bypass device is installed horizontally and is equipped with an automatic air vent. A circulation pump for home heating will help you in the cold.

The use of a circulation pump for heating systems significantly improves their performance characteristics. In addition, such pumps, thanks to which the water heated by the boiler enters all elements of the heating systems much faster and less cooled down, allow saving on energy carriers (electricity, fuel for the boiler). The effectiveness of the use of circulation pumps as part of heating systems largely depends on the correct choice of such equipment, made on the basis of its technical characteristics.

Types and main characteristics

Before understanding which circulation pumps for heating systems have specifications, you should get to know various types such equipment. By design, circulation pumps are distinguished:

• with a "wet" rotor;
• with a "dry" rotor.

The design feature of devices of the first type is that the moving elements of their rotor assembly are constantly in contact with the pumped medium, which ensures not only their lubrication, but also effective cooling. In addition, the operation of such equipment, the rotor of which is constantly in a liquid medium that perfectly absorbs all vibrations, is characterized by a minimum noise level. The advantages of circulation pumps with a "wet" rotor are also compact dimensions, ease of installation and maintenance. If we talk about the shortcomings of such hydraulic machines, then the most significant of them is low efficiency.

The design of the circulation pump with a "wet" rotor

In circulation pumps with a "dry" rotor, as it becomes clear already from their name, the elements of the rotor assembly do not come into contact with the liquid coolant, which endows such devices with both advantages and disadvantages. The most significant advantages of hydraulic machines of this type are high productivity and efficiency, reaching up to 80%. Circulation pumps with a "dry" rotor are equipped with powerful thermal stations and heating systems industrial use, in domestic heating systems, as a rule, they are not used. Among the disadvantages of hydraulic machines with a "dry" rotor, they usually name a rather high noise level, as well as the complexity of installation and maintenance.

The device of the circulation pump with a "dry" rotor

The technical capabilities and operating conditions of circulation pumps for heating systems are determined by a number of characteristics.

Performance

This parameter indicates the amount of fluid that the device is able to pump per unit of time of its operation. The unit of measurement of this parameter is m 3 / hour.

pressure

Head is also called hydraulic resistance. The magnitude of the pressure generated by the circulation pump is measured in meters or decimeters of the water column.

Supply voltage

The type depends on this parameter. electrical network(single or three phase) to which a pump can be connected. Naturally, for installation in heating systems of residential buildings, one should choose hydraulic machines operating from an electrical power supply network with a voltage of 220 V.

Power consumption

This characteristic depends both on the specific model of pumping equipment and on the mode in which it operates. Many models of circulation pumps designed for domestic heating systems can provide several speeds for pumping water. On the case of such pumps, as a rule, there is a special plate on which the power consumption and current strength corresponding to each of the operating modes are indicated. The predominant majority of circulation pumps for domestic heating systems are characterized by a power consumption in the range of 50–70 W.

Table 1. Main parameters and features of the choice of circulation pumps for heating

Maximum coolant temperature

When choosing a circulation pump for a heating system according to this parameter, preference should be given to models designed to work with a working medium whose temperature can reach up to 110 °.

Dimensional parameters

This includes such characteristics as the diameter of the threaded part of the mounting elements of pumping equipment and the mounting length of its body. Most of the circulation pumps used in domestic heating systems simply cut into the pipeline and connect to its elements using union nuts - "American". Quite often, both the nuts themselves and the pipes for connecting the device to the pipeline system are already included in its factory package. The most common mounting diameters for circulation pumps used to equip domestic heating systems are 1 and 1.25 inches (25 and 32 mm, respectively). The installation length of household circulation pumps can be 130 or 180 mm.

Electrical protection class

Most of the modern models of circulation pumps for domestic heating systems according to the international classification correspond to the IP44 protection class. Manufacturers provide pumping equipment of this class with protection against ingress of solid foreign particles larger than 1 mm into its internal part. This is indicated by the first number 4 in the marking. The next number 4 in the designation of the protection class indicates that the electrical part of the equipment is insured against liquid drops and splashes flying at any angle.

Maximum outlet fluid pressure

On the case of many models of circulation pumps you can find information about this characteristic. As a rule, at household equipment this parameter does not exceed 10 bar. From a practical point of view, it says nothing, characteristics such as pressure and performance are much more important.

Trademark and manufacturer

When choosing circulation pumps for heating systems (however, like any other technical devices), it is better to give preference to products from well-known manufacturers that are more serious about quality issues and provide reliable guarantees.

Technical characteristics of circulation pumps for heating systems, as a rule, are included in the designation of their models. Using such designations, in particular, the following parameters can be immediately determined: the liquid pressure created by the device, the diameters of its suction and discharge pipes, and the installation length.

Rules and features of choice

You should start choosing a specific model of the circulation pump only after the heating system has been designed and the total length of its closed circuit becomes known. In addition to the length of the heating system circuit, the number of radiators with which it will be equipped also influences the choice of the circulation pump. Only after receiving all this data, you can high precision determine what performance the circulation pump should have and what size of the coolant pressure in the system it should provide. The performance of the circulation pump for the heating system is very important to calculate based on the lowest outdoor temperature when pumping device will run at maximum load.

When choosing a circulation pump for a heating system according to the characteristics of such a device, you can focus on the following recommendations from experienced professionals.

Circulation pumps used to pump water or a thin homogeneous liquid are an important part of the heating system. By ensuring uniform movement of the coolant through the pipes, they achieve uniform heat distribution, improving performance.

In addition to ensuring the movement of fluid in a circle inside the heating pipes, the pump can operate in recirculation mode. When calculating its parameters, they try to take into account friction losses and resistance of the coolant. The height of the top point, piping, heating appliances have little effect on the operation of the pump, because the liquid supplied to the pipeline in one direction pushes it in the opposite direction. Therefore, when selecting a circulation pump, you can stop at a lower power to ensure the normal movement of the coolant.

Calculations

The device of a circular pump is a mechanism in the form of a rotor placed inside a metal case. A wheel with several blades (impeller) is fixed on the rotor shaft. When the pump motor is turned on, the wings rotate and move the liquid throughout the heating system.

The principle of operation is the forced transportation of water inside the closed circuit of the heating system, in other words, ensuring the circulation of the coolant through pipes and radiators. Proper selection of such a unit ensures its correct operation without unnecessary costs.

Pump power calculation table.

Before choosing a pump, it is necessary to determine the volume of water that will pass through the heating boiler in one minute. It is these parameters that manufacturers lay down, equalizing the flow rate of the liquid with the power of the boiler. If a heater of 20 kW is installed, then in one minute it will pass 20 liters of coolant.

Next, it is necessary to calculate the water flow in each ring of the heating system (knowing the power of the radiators, this process is not difficult). The flow rate of the coolant in the pipes directly depends on their diameter. Inch pipes transport 30 liters of liquid per minute, two-inch - 170 liters / min. The average speed of water movement along heating system equal to 1.5 m/s. The power of the circulation pump can be selected according to the length of the pipeline. For a ten-meter section of the heating main, a pressure of 0.6 m is sufficient. Therefore, in order to establish a water supply through a 100-meter heating system, it is necessary to select a pump capable of delivering a pressure of 6 m.

You can also calculate the power using the following formula:
Qpu=Qn/1.163xDt [m3/h], where

• Qpu (measured in m3/h) - coolant supply at the design point;
• Qn (measured in kW) - consumed heat in the heated area;
• Dt is the temperature difference in the forward and return pipelines (average 10-20 °С);
• 1.163 is the specific heat capacity of water.

Such calculations are not absolute, they are rather standard. There are complex formulas for more accurately determining the required power of the circulation pump, but it will not be easy to understand them without certain knowledge in the field of physics. Yes, and the units are mass-produced, so adjust their operating parameters to individual systems heating is only approx. Therefore, experts advise to select a pump with a power reserve of 5 - 10% of that which was obtained as a result of calculations. There are devices with several settings. During operation, you can choose optimal parameters work.

Possessing such simple knowledge and enlisting the help of the seller, you can choose the circulation pump of the optimal power at which heat will be provided throughout the room.

Kinds

The fluid pressure is created by rotors on which the blades are fixed. More often, one rotor is involved in the design of the circulation pump for heating, but you can find an option with two. An important condition for operation is the absence of air in the system.

According to the device, the execution of the working part, the pump can be with a wet rotor or dry. Those with a wet rotor are specially designed to be in the pumped medium with the impeller. Changes often affect the design of the housing, made in such a way that liquid enters through the existing technological gaps, its constant movement cools the motor, lubricates moving parts.

Circulation pumps equipped with a wet rotor do not have an oil seal, a sliding mechanical seal. The rotor is completely in the pumped medium, which provides cooling and lubrication of parts. As the rotor rotates, water constantly passes through the sleeve. The best effect is observed if the pump is located horizontally, then no air pockets are formed inside the wet rotor.

The fact that all parts of the heating circulation pump are constantly in the liquid, not only lubricates the moving parts, but also absorbs vibration noise, so they are practically silent. To check its operation and the correct rotation of the rotor, use a special device or visually, opening the back plug. The absence of noise during operation allows them to be widely used for individual heating. In addition, the execution of the design of pumps equipped with a wet rotor can be ordinary - for heating systems, and special - for water supply. hot water where the possibility of mineral deposits is taken into account.

In such cases, the liquid does not wash the rotor, does not lubricate the moving parts. The main advantage of this type is the ability to pump a larger volume of liquid. The advantage is manifested in the installation of engines of greater power. In addition, the device comes with a solid shaft, on which a motor with impellers or with a coupling connection is installed - here it is possible to replace the electric motor, install another with larger parameters.

To prevent water ingress, a mechanical seal, an oil seal is installed between the pump and the electric motor. During rotation, a thin water film appears between the surfaces. Due to the pressure created inside the pump, the film additionally seals the rotating parts. The main material in the manufacture of rings is agglomerated coal, sometimes under difficult working conditions, the seal is made of ceramics, stainless steel.

According to the design of the execution, the device of the circulation pump is with a flange connection of the motor and a coupling. If the branch pipes (suction, pressure) are located on the same axis, then this is a direct-flow version, which allows their installation directly in the line. A frame is provided for mounting. In addition to fastening to the frame of the pump, electric motor, it itself is installed on the foundation.

Why is it necessary

The heating circuit with a circulation pump eliminates some of the problems that are typical for the natural type of coolant movement. After all, if the water at the outlet of the radiator is cold, when it also reaches the extreme radiators, it is also barely warm, then it enters through the return cold water makes the boiler work at the maximum of its capabilities. At the slightest design miscalculations, installation errors, the distortion in temperature becomes even more noticeable, especially when it is necessary to warm up the room quickly, or when the system is first started, which can be seen from the operation of the boiler, from distant registers.

The use of a circulation pump eliminates these disadvantages. First of all, the requirements for compliance with pipe slopes, their flow area are reduced, all plugs caused by temperature differences are eliminated. The heat transfer occurs evenly, the temperature of the coolant at the inlet / outlet of each radiator is almost the same, and the difference between the coolant before entering the system and returning it to the boiler is several degrees, within ten.

The pump greatly simplifies the design of the piping system.

What does it give? Stabilizes the boiler. If the difference is several degrees, then a smaller volume of gas is spent on heating, the duty cycle is reduced. For example, we need a coolant temperature of 70. Initially, when the water is cold, the boiler operates at maximum power, but as it warms up over time, the picture changes.

In the spring and autumn months, when the house is slightly cool at night and comfortable during the day, teamwork boiler, automation, circulation pump can maintain coolant performance within 40 °, which is impossible with natural circulation.

The coolant returns in one pass through the system, having lost only 5 °, its temperature is 65 °, while it is the same in the rooms, the heat is distributed evenly over all radiators, and the automation turns off the burner according to the programmed indicators.

The next switch on will occur when the temperature drops. This is an economical mode of operation, in which there is no constant heating, but only the maintenance of the required temperature parameters. If thermostats are installed on all radiators, then by setting the necessary temperature parameters on each register, for example, in the kitchen, in warm room on the south side, by lowering them, we will get additional savings.

Additional Benefits

When using a heating circulation pump, a decrease in the diameter of the pipes being laid is allowed. This is manifested in additional cost savings, allows you to reduce the volume of water in the system, respectively, the volume of gas is reduced to maintain the desired temperature, and the heating time is reduced.

grundfos pump.

But there are a number of parameters that make adjustments to the calculations. The main ones are: the area of ​​\u200b\u200bthe house (usually residential is taken into account), the thermal conductivity of materials, the friction of the liquid inside the pipes. The last requirement, given the fluidity of the liquid, may seem unreasonable, but it works. The automatic control option installed on the circulation pump will allow you to heat the house before your arrival, the cottage before the weekend, and significantly save electricity. When buying a product, do not forget to pay attention to the warranty, service life.

There are several major manufacturers of pumping equipment that have long proven themselves in terms of quality and reliability. These are the brands Grundfos, DAB, WILO, Pedrollo. The main difference in their work is the maximum implementation of production automation processes, which, affecting many stages, allows you to get high-quality products.

It's no secret what water heating most common in urban residential buildings and private cottages. And an integral part of the system, along with the boiler, is a circulation pump, the function of which is to ensure the movement of water along the “boiler-heating circuit-boiler” circuit. Of course, you can do without a circulation pump, thereby making it, but this will entail an increase in pipe diameters, the presence of slopes during laying, which will only complicate the heating system.

When the term "circulation pump" is mentioned, the pump "with a wet rotor" is immediately presented. And this is not accidental, since it is this type that is most suitable for providing heating in private houses and small rooftop boilers. The device of the circulation pump with a wet rotor determines its advantages such as compactness and noiseless operation.

This type of pump got its name because of the presence of water cooling motor. The liquid pumped by the pump is also used for for parts lubrication.

Although there are currently a lot of manufacturers of pumping equipment, the basic device of a wet rotor circulation pump is the same as that of Wilo that u Grundfos.

AT cast iron or steel body attached to the motor shaft closed Working wheel made of heat-resistant composite material. It represents two parallel drives which are interconnected by radially curved blades. One of the discs has a hole for the inlet of the working fluid, the second has a hole for mounting the impeller on the motor shaft.

In the pump housing along the periphery of the impeller, a spiral hole is made in the form confuser. Its purpose is to convert the kinetic energy of the fluid flow into static pressure, as well as to collect and drain water in the right direction.

The impeller is fixed on the shaft rotor, which is washed and cooled by pumped water. motor stator hermetically separated from the rotor separating glass with wall thickness 0.1 - 0.3 mm. The glass is made of ferritic stainless steel or carbon fiber.

The circulation pump rotor is fixed on end face graphite or ceramic plain bearings which are also cooled by the pumped water.

Also on the front wall of the engine housing there is screw plug to remove air from the pump.

The external difference between the design of a circulation pump with a wet rotor and air-cooled electric motor pumps (with a dry rotor) is the absence of fins on the motor housing and an impeller at its end.