Differences between pumps with "wet" and "dry" rotor. Circulation pump for heating with dry and wet rotor Circulation pump with dry rotor

Heating systems are divided into systems with natural (gravitational) and forced circulation. In systems with forced circulation, the installation of a circulation pump is mandatory. Its task is to ensure the movement of the coolant through the system at a given speed. And in order for him to cope with his task, he must choose the right circulation pump.

Purpose and types

As already mentioned, the main task of the circulation pump is to provide the required speed of movement of the coolant through the pipes. For systems with forced circulation, only under such conditions will the design capacity be achieved. During the operation of the circulator, the pressure in the system increases slightly, but this is not its task. It is rather a side effect. There are special ones to increase the pressure in the system.

There are two types of circulation pumps: dry and wet rotor... They differ in design, but perform the same tasks. To choose which type of circulation pump you want to install, you need to know their advantages and disadvantages.

Dry rotor

It got its name due to the design features. Only the impeller is immersed in the coolant, the rotor is in a sealed casing, it is separated from the liquid by several O-rings.

Circulation pump device with dry rotor - only impeller in water

These devices have the following properties:

• They have a high efficiency - about 80%. And this is their main plus.
• Requires regular maintenance. During operation, solid particles contained in the coolant fall on o-rings breaking the tightness. To prevent depressurization and maintenance is necessary.
• The service life is about 3 years.
• When working, they publish high level noise.

This set of characteristics is not very suitable for installation in heating systems of private houses. Their main plus is high efficiency, which means less power consumption. Therefore, in large networks, circulation pumps with a dry rotor are more economical, and they are mainly used there.

Wet rotor

As the name implies, this type of equipment contains both the impeller and the rotor in the liquid. The electrical part, including the starter, is enclosed in a metal sealed glass.

Glandless pump arrangement - dry electrical part only

This type of equipment has the following properties:

• The efficiency is about 50%. Not the best indicator, but for small private heating systems this is not critical.
• Maintenance is not required.
• The service life is 5-10 years, depending on the brand, operating mode and condition of the coolant.
• Almost inaudible during operation.

Based on the above properties, it is not difficult to choose a circulation pump by type: most stop at devices with a wet rotor, since they are more suitable for working in an apartment or a private house.

How to choose a circulation pump

Each circulation pump has a set of technical characteristics. They are selected individually for the parameters of each system.

We select technical characteristics

Let's start with the selection of technical characteristics. There are a bunch of formulas for a professional calculation, but for the selection of a pump for the heating system of a private house or apartment, you can get by with average rates:

It is not difficult to choose a circulation pump for heating following these rules. Elementary calculations. But I must say that these figures are average. If your house at some point is very different from the "average", you need to make adjustments either upward or downward in technical characteristics. For example, you insulated the house well, the capacity of the previously purchased boiler turned out to be excessive. In this case, it makes sense to take a pump with a lower performance. In the opposite situation - it is chilly in the house in extreme cold - you can put a more efficient circulator. He will temporarily solve the problem (in the future, it is necessary to either insulate or change the boiler).

Model selection

When choosing a specific model, pay attention to the graph with the pressure characteristic of the pump. On the graph, you need to find the point at which the values ​​of head and productivity intersect. It should be in the middle third of the curve. If it does not fall on one of the curves (there are usually several of them, characterizing different models), take the model whose graph is closer. If the point is in the middle, take the less productive one (the one that is located below).

What else to pay attention to

There are several more items in the technical characteristics of circulation pumps that are worth paying attention to. The first is the permissible temperature of the pumped medium. That is, the temperature of the coolant. V quality products this indicator is in the range from + 110 ° C to + 130 ° C. In cheap ones, it can be lower - up to 90 ° C (and in fact 70-80 ° C). If your system is designed as a low-temperature one, this is not scary, but if there is a solid fuel boiler, the temperature to which the coolant can be heated is very important.

It is worth paying attention to the maximum pressure at which the pump can operate. In the heating system of a private house, it rarely exceeds 3-4 atm (this is for two-storey house), and normally it is 1.5-2 atm. But still, pay attention to this indicator.

What else to pay attention to is the material from which the case is made. The optimal one is cast iron, the cheaper one is made of special heat-resistant plastic.

Connection type and size. Circulation pump can be threaded or flanged. The thread can be external and internal - appropriate adapters are selected for it. Connecting sizes can be: G1, G2, G3 / 4.

It is also worth paying attention to the availability of protection. Can be dry run protection. In circulating pumps with a wet rotor, it is very desirable, since the cooling of the motor occurs due to the transported medium. If there is no water, the motor overheats and fails.

Another type of protection is overheating protection. If the motor heats up to a critical value, the thermostat cuts off the power, the pump stops. These two functions will extend the life of the equipment.

Manufacturers and prices

Name	Performance	Pressure	Number of speeds	Connecting dimensions	Maximum working pressure	Power	Body material	Price
Grundfos UPS 25-80	130 l / min	8 m	3	G 1 1/2 "	10 bar	170 watts	Cast iron	15476 rbl
Caliber NTs-15/6	40 l / min	6 m	3	external thread G1	6 atm	90 watts	Cast iron	2350 rbl
BELAMOS BRS25 / 4G	48 l / min	4.5 m	3	external thread G1	10 atm	72 watts	Cast iron	2809 rbl
Jileks Compasses 25/80 280	133.3 l / min	8.5 m	3	external thread G1	6 atm	220 watts	Cast iron	6300 rbl
Elitech NP 1216 / 9E	23 l / min	9 m	1	external thread G 3/4	10 atm	105 watts	Cast iron	4800 rbl
Marina-Speroni SCR 25 / 40-180 S	50 l / min	4 m	1	external thread G1	10 atm	60 watts	Cast iron	5223 rbl
Grundfos UPA 15-90	25 l / min	8 m	1	external thread G 3/4	6 atm	120 watts	Cast iron	6950 rbl
Wilo Star-RS 15 / 2-130	41.6 l / min	2.6 m	3	internal thread G1		45 watts	Cast iron	5386 rbl

Please note that all specifications presented for moving water. If the coolant in the system is an antifreeze liquid, adjustments must be made. For data relevant to this type of coolant, you will have to contact the manufacturer. In other sources, similar characteristics could not be found.

Dry rotor pumps are used for pumping liquids with high head. They are best suited for the supply of coolant and aggressive media. Unlike glandless pumps, these pumps do not have liquid in contact with the motor.

Another difference from glandless pumps is the way in which the pump housing / shaft is insulated. This is achieved using stuffing box or mechanical 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 an integrated electronic speed control unit, which, thanks to modern technology can be installed on motors with high power output.

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

In-line pumps
Pumps for which the suction and discharge nozzles are on the same axis and have the same nominal bore are called in-line pumps. In-line pumps are equipped with standard air-cooled flanged electric motors. This type of pump is considered to be 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 electric motor air cooling... The liquid enters the pump axially and exits radially. Motor brackets or supports are standard on pumps.

Cantilever pumps
Data centrifugal pumps have an axial inlet and a radial outlet of liquid from the pump. The pump and the 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 stuffing box seal. The nominal passage of such pumps is determined by the discharge pipe. The suction port has a larger nominal size.

Shaft seal
The shaft can be sealed (in standard configuration or as an option, in the case of overhung pumps) from the atmosphere using STU or stuffing box seal. Below is a description of these two types of seals.

STU pump with dry rotor

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

One (dynamic) ring rotates with the shaft, while the other (static) ring 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 operating mode of the pump, several types of friction of the mating surfaces are possible: mixed friction, boundary friction or dry friction, and the latter (occurring in the absence of a lubricating film) causes immediate destruction of the surfaces.

Service life depends on operating conditions such as fluid composition and temperature.

Stuffing box seals
High quality synthetic yarns such as Kevlar® or Twaron®, PTFE, porous graphite yarns, synthetic mineral yarns and natural fibers such as hemp, wadding or ramie are used as packing materials.

Material for oil seals is produced in the form of threads or compressed skeins, dry 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 shape it. Then, the packing ring is wrapped around the pump shaft and tightened with a ferrule.

Mounting types

Permitted mounting methods
In-line pumps are designed for horizontal and vertical installation directly on the pipeline.
Sufficient space must be left to dismantle the motor and pump elements.
When connecting the piping, stress and weight of the piping must not be transmitted to the pump, and the pump should be supported on supports (if any).

Unacceptable installation methods
Installation with the motor and terminal box pointing downward is not permitted.
If the motor power exceeds a certain level, the manufacturer should be consulted before installing the pump in a horizontal position.

- Sectional view of a centrifugal pump high pressure
- Features of high pressure centrifugal pump

High pressure centrifugal pumps

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

Due to the variable number of stages, high-pressure centrifugal pumps develop higher pressures than low-pressure single-stage centrifugal pumps.

Some pumps have up to 20 stages. Thus, they can deliver 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.
A block pump installation with the motor and terminal box pointing downward is not permitted. All other mounting methods are considered permissible.
For detailed information on installation methods, see the installation and operating instructions.

It was believed by many that for domestic use it is necessary to take circulation pumps with a wet rotor. Dry rotary circulation pumps were used for industrial use.

It was believed that dry rotor pumps are oversized and noisy. However, large manufacturers began to produce more and more household models of circulation pumps with a dry rotor.

The industry uses dry rotor circulation pumps.

In the domestic version, circulation pumps with a wet and dry rotor are used. For industrial needs, pumps with a wet rotor are not used, since they can be produced with a power of up to 3 kW and they are not widely used.

Advantages of circulation pumps with a dry rotor of industrial design: the quality of the coolant is not important for them, they have good maintainability. The downside of these pumps is that they are large, make a lot of noise, so they are installed in separate rooms, consume a lot of electricity.

As for the domestic version of the pump with a dry rotor, its advantages:

has a higher efficiency;

the purity of the coolant is not important for him;

has good maintainability, and spare parts are cheaper than pumps with a wet rotor;

in size, it almost does not differ from the wet-rotor analogue.

The downside is a lot of noise during operation and the need for regular replacement of the mechanical seal.

The disadvantages of circulation pumps with a dry rotor are the advantages for a pump with a wet rotor: noiselessness, no mechanical seal. The disadvantage is that the quality of the coolant is of great importance during operation. The worse the quality of the pumped liquid, the faster the pump can fail.

Considering all the pluses and minuses of the considered pumps, we can draw the appropriate conclusions. If the quality of the coolant is not important to you, then it is better to choose a pump with a wet rotor, but it is not known what will happen to the rest of the heating system.

If you want everything to work smoothly, it is better to use a motor with a dry rotor, but you need to take care of the quality of the coolant.

As for the noise, everyone decides for himself, because the pump does not come into sight so often. The efficiency is not so important, since the difference in percentage is small, but the absence of the need to replace the mechanical seal is a big plus.

However, maintenance should be carried out regularly together with an inspection of the entire heating system by a specialist.

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

In addition to ensuring the movement of liquid in a circle inside the heating pipes, the pump can operate in recirculation mode. When calculating its parameters, they try to take into account the friction losses and the resistance of the coolant. Height of the top point, pipe routing, heating appliances have little effect on the operation of the pump, because the liquid flowing into the pipeline in one direction pushes it in the opposite direction. Therefore, when selecting a circulation pump, it is possible to stop at a lower power in order 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 running, the wings rotate and propel fluid throughout the entire heating system.

The principle of operation consists in the forced transportation of water inside a closed circuit of the heating system, in other words, ensuring the circulation of the coolant through pipes and radiators. Competent selection of such a unit ensures its correct operation at no extra cost.

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 are laid by manufacturers, equalizing the flow rate with the boiler power. If a 20 kW heater is installed, then in one minute it will pass 20 liters of coolant.

Further, it is necessary to calculate the water consumption in each ring of the heating system (knowing the power of the radiators, this process will not be difficult). The flow rate of the coolant in the pipes directly depends on their diameter. Inch pipes transport 30 l of liquid per minute, two-inch - 170 l / min. The average speed of movement of water through the heating system is 1.5 m / s. The power of the circular pump can be selected taking into account 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 head of 6m.

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

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

These calculations are not absolute, but rather standard. There are complex formulas for a more accurate determination of the required power of the circulation pump, but it will not be easy to understand them without certain knowledge in the field of physics. And the units are mass-produced, so adjust them operating parameters for individual heating systems is possible only approximately. Therefore, experts advise to select a pump with a power reserve of 5-10% of that which was obtained as a result of the calculations. There are machines with several setting modes. In the course of their operation, you can choose the optimal operating parameters.

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

Views

The fluid pressure is created by the rotors on which the blades are fixed. More often, one rotor is involved in the design of a 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 case, made in such a way that fluid 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 a gland, mechanical seal. The rotor is completely in the pumped medium, which provides cooling and lubrication of parts. As the rotor rotates, water constantly flows through the sleeve. The best effect is observed if the pump is located horizontally, then it does not form air congestion 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 design of pumps equipped with a wet rotor can be conventional - for heating systems, and special - for water supply. hot water where the possibility of mineral deposits is taken into account.

In such cases, the fluid does not wash over the rotor and 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 larger motors. In addition, the device comes with a solid shaft, on which a motor with impellers or with a coupling is installed - here it is possible to replace the electric motor, install another with large parameters.

To exclude the ingress of water, a mechanical seal, an oil seal, is installed between the pump and the electric motor. When rotating, a thin water film appears between the surfaces. Due to the pressure generated inside the pump, the film additionally seals the rotating parts. The main material for the manufacture of rings is agglomerated coal; sometimes, under severe operating conditions, the seal is made of ceramics, stainless steel.

According to the design of the execution, the device of the circulation pump can be flange connection motor and coupling. If the nozzles (suction, discharge) are located on the same axis, then this is a direct-flow design, which allows their installation directly into the line. A frame is provided for fastening. In addition to being attached to the pump frame, the electric motor, it itself is installed on the foundation.

What is it for

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

The use of a circulation pump eliminates these disadvantages. First of all, the requirements for compliance with pipe slopes, their flow section are reduced, all plugs caused by temperature differences are eliminated. Heat transfer occurs evenly, the temperature of the coolant at the inlet / outlet of each radiator is practically 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 do? Stabilizes the operation of the boiler. If the difference is a few degrees, then a smaller volume of gas is spent on heating, the operating 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, the joint operation of the boiler, automation, and circulation pump can maintain the coolant indicators within 40 °, which when natural circulation impracticable.

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

The next switching 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 required temperature parameters on each register, for example, in the kitchen, in warm room on the south side, lowering them, we get additional savings.

Additional benefits

When using a heating circulation pump, it is allowed to reduce the diameter of the pipes to be laid. This manifests itself 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 ​​the house (usually the residential area is taken into account), the thermal conductivity of materials, the friction of the liquid inside the pipes. The latter requirement may seem unreasonable given the fluidity of the fluid, but it works. The automatic regulation option installed on the circulation pump will allow you to heat the house before your arrival, the summer cottage before the weekend, and will significantly save energy. When buying a product, do not forget to pay attention to the warranty and service life.

There are several major manufacturers pumping equipment, long-established quality and reliability. These are 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.