Water flow switch for a pump: characteristics, principle of operation, installation. Water flow relay - purpose, principle of operation and independent connection Water flow relay petal

This article will discuss devices used to protect against dry running. You will learn their types, design features and operating principles, as well as all the significant advantages and disadvantages.

It is with their help that it is possible to avoid the main and most well-known problems that are associated with the breakdown of pumping equipment or its excessively rapid wear.

1 General information about the water flow switch

As practice shows, the main reason for the failure of most water pumps is overheating, which is a consequence of idle operation of the unit, the so-called “dry” operation, when the pump is turned on but does not pump water.

This is explained by the fact that the device of any submersible requires constant cooling of the power unit by the working medium, and in the case of surface devices - by the pumped liquid. Moreover, for a deep sample this parameter is extremely important, since it essentially consists of a large number of parts that constantly interact with each other.

For example, centrifugal deep well pump after switching on, it puts into operation several stages of impellers that rotate simultaneously. Running them without fluid is simply wearing out the device for no reason. The situation is similar with surface models.

1.1 Why use a flow switch?

Dry running submersible pump possible in the following situations:

• When the unit is incorrectly selected, its productivity exceeds the well's flow rate, and the dynamic water level of the well falls below the depth of its installation;
• If pumping is performed from a small excised source without outside supervision;
• Idle operation is possible due to internal clogging of the hose or its mechanical damage, which cause loss of tightness of the hose, which occurs quite often;
• For circulation pump dry work is possible at the moment low pressure supplying water to the pipeline to which it is connected.

Be that as it may, it is not always possible to carry out constant monitoring by constantly being present when the pump is operating, so it is necessary to take care of additional mechanisms that will monitor the presence of water flow and turn the pump on and off when necessary.

The water flow relay, also known as “”, is exactly such a device. There is no need to install a flow switch in the following cases:

• If water is taken by a low-power pump from a high-yield well;
• If you are constantly present when the pump is operating, and you can turn it off yourself when the water level drops below the permissible norm.

In all other cases, the installation of a water flow switch is required, since it not only extends the life of the pump, but also significantly increases the ease of its operation. At a minimum, automating its work in terms of protection against possible problems.

2 Design features and principle of operation

There are several types of water flow switches and similar safety devices, each of which is equipped with different automation that turns the pump on and off in response to certain indicators.

Most common triggers:

• Liquid level (water level switch);
• Liquid pressure level at the outlet pipe (press control);
• Presence of water flow (flow switch);
• Temperature working environment(thermal relay.

Let's look at each of these devices in more detail.

2.1

Such a device consists of two main structural elements: a reed switch and a petal (valve) on which a magnet is mounted. The reed switch, which acts as a contact that responds to changes in the position of the magnet, is located outside the water flow and is reliably insulated.

On the opposite part of the structure there is a second magnet, which creates a reverse force, which is necessary to return the petal to its original position at the moment the fluid flow weakens.

When the pump is filled with water, it acts on the petal, causing it to rotate around its axis. The movement of the petal brings the magnet closer to the reed microswitch, which is activated by the resulting magnetic field.

The reed switch connects the contacts of the pump and the electrical network, as a result of which the device is turned on. As soon as the flow of liquid has stopped, the petal, which no longer receives additional pressure, returns to its original position under the influence of the force of an additional magnet and the contacts open.

Advantages of the petal flow switch:

• Does not reduce water supply pressure;
• Works instantly;
• No delay between retriggers;
• Using the most accurate circulation trigger to turn on the pump;
• Simplicity and unpretentiousness of design.

There are also flow switches, the valve design of which is made without return magnets, where the second magnet is replaced by conventional springs. However, such relays in practice show less stability, since they are overly susceptible to the influence of small pressure surges in the water flow.

2.2 Press control - water flow switch combined with a pressure switch

Press control gives a command to turn on the pump only when the level of water pressure in it rises to a certain level (this indicator is adjustable, most often it ranges from 1 to 2 Bar), the pump is turned off, due to the opening of the contacts, within 5-10 seconds after completely stopping the flow of water pumped out of the well.

Such devices can be used either in conjunction with a hydraulic accumulator, performing the function of controlling a pumping station, or installed directly on the outlet pipe of the pump, protecting it from idling.

Press control, in comparison with a conventional relay that reacts to changes in the level of water flow, has one significant drawback - if it is installed on a surface-type pump, then each time before turning it on you must personally fill the unit with water. The problem is solved by installing additional check valves, but this is far from a panacea.

2.3 Thermal water flow switch

Among all the above types of safety devices, it is the thermal relay that has the most complex design. The technology of its operation is based on the thermodynamic principle, according to which the thermal difference between the temperature of the water flow in the pump and the temperature to which the relay sensors are set is compared.

When the thermal relay is connected to the pump, which is located inside, a certain amount of electricity is constantly supplied to it, which is spent on heating the sensors to a temperature several degrees higher than the temperature of the liquid being measured.

In the presence of water flow, the sensors are cooled, which is fixed by a microswitch. The thermal change is a signal after which the connection between the pump contacts and the electrical network is made. As soon as the flow of water from the well stops, the microswitch disconnects the contacts and the pump turns off.

In addition to downhole units, a thermal flow relay is ideal option Dry running protection for the circulation pump.

The thermal relay allows not only to increase the useful life of the circulation device, but also to save a considerable amount of electricity, since the thermal relay automatically turns off the pump when pressurizing the water flow in the heating main is not required.

When heating device is turned off and the water in the system is cold - no work is needed, and the thermal relay keeps the contacts closed. When you turn on the boiler, as the water in the pipes reaches the set temperature, the thermal relay turns on the circulator, and it begins to build up pressure to the required level.

It is worth noting that most leading manufacturers of circulation pumps independently install thermal flow switches on their devices. This is mainly typical for premium class pumps. This is due to their high cost and complexity of design.

2.4 Water level switch

The simplest and most utilitarian version of a safety device for a water pump is a water level switch, commonly known as a float switch.

A “float”, which must be mounted inside the source 20-25 centimeters above the level of the pump, monitors the amount of water in the source, and as soon as the water drops below float sensor, the pump is automatically switched off.

The relay itself is connected to the phase that is supplied to power the pump. The adjustment is made by changing the length of the adjustment cable. Better quality floats can be customized additional functions, but this already applies to expensive equipment models, which household use are quite rare.

The float switch is a proven means of protection for any well and drainage devices, however, the water level switch cannot be used in deep wells, since serious difficulties arise with its precise tuning.

Also, floats do not always work well in cramped conditions, when the difference between the diameter of the well and the pump is only a few tens of millimeters. In this case, there is simply no point in using it, since the operation of the float will become too unstable.

Use float switches as on conventional ones well pumps, and on drainage samples. Moreover, there they are even more in demand, because unlike standard wells, the working environment tends to constantly decrease. Dry run drainage models harms no less than borehole or well pumps.

2.5 Nuances of installing a water flow switch

Paddle switches are mounted either at the pump inlet or at the valve inlet. Their task is to record the initial entry of liquid into the working chamber, and therefore contact with it must be detected first of all on the relay itself.

Pressure control units are installed only with the help of specialists, as they require adjustment. They are installed in the same way as the petals, by connecting the input to pumping device. However, unlike conventional petals, pressure switches are almost always used in conjunction with.

Thermal relays are rarely used separately, since the thing is too expensive. It will most likely be connected at the assembly stage of the pump itself. However, good master will certainly be able to cope with the installation of this device. The complexity of the installation lies in the need to mount several sensitive thermal sensors, and then bring them together.

2.6 Example of operation of a water flow switch (video)

The water flow switch is a multifunctional device, the main task of which is to automate the pump and regulate the water supply. The sensor turns water on and off depending on its availability in the system. We supply sensors made only from high-quality environmentally friendly materials, thanks to which the water flow switch can interact even with drinking water without distorting its composition. At the same time, our price for water flow sensors is lower than in city stores.

Sensors are mainly connected to pumps with high power, as they effectively protect the pump from overheating and other possible problems. Thanks to this, the water flow switch for the pump extends its service life and ensures ease of use of the pump. The advantages of a flow switch for a pump are: small size, high sensitivity, multifunctionality, affordable price, long service life. If you do not have time to constantly monitor the operation of the pump, then the sensor will do it for you.

When installing a pressure control sensor, you should seek the help of specialists, since initially the flow switch for the pump needs to be configured. Installation is carried out in the following way: The inlet water flow switch is connected to the pumping device. When there is a sufficient volume of water flow, the device is activated due to the pressure on the sensor blade. When the water flow decreases, the sensor blade returns to its original position and the water supply stops. You can buy a water flow sensor for a pump in Moscow at the best price using a payment method convenient for you.

Effective operation of pumping equipment is the key to uninterrupted water supply and functioning of the heating system in a private home. If you want to enjoy the benefits of civilization every day, you must make every effort to set it up correctly.

The solution to this problem includes a wide range of work, the main one being the installation of additional equipment that will help to clearly monitor possible failures in the system and prevent pump failure.

The most popular and useful in everyday life are such auxiliary devices as: a temperature sensor, as well as a water flow sensor. It is the properties and operational features of the latter device that will be discussed in this article.

1 Purpose and benefits

In everyday life, an emergency switching on of a pump without water periodically occurs, which is considered extremely dangerous, because it can cause equipment failure. Popularly called “dry running” leads to overheating of the engine and deformation of parts.

Such negative changes occur because the water in the system performs a lubricating and cooling function. Operating in “dry running” mode, even for a short time, has a negative effect on the equipment, be it circulation or. To avoid such problems, the pumping station is equipped with automation - a water flow sensor. It will prevent negative changes in the system and avoid the cost of repairing the pump.

The water flow sensor is a device for controlling a pumping station in. In addition, this automatic device serves to increase the pressure and protect the pump, which is used in heating systems Oh.

The principle of operation of the sensor is that it monitors the power of the liquid flow and independently turns on or off the pumping station when a flow of water appears and passes through it. In this way, it is possible to prevent possible “dry running”, because the submersible or circulation pump drives the system and raises the pressure inside it only when required.

Installing a water flow sensor entails a number of positive points in operation pumping station:

• saving energy costs;
• reducing the risk of equipment breakdown;
• increasing pump life.

1.1 Design and operating principle

As has already become clear, the built-in water flow sensor is used in heating and water supply circulation systems of private houses. His job is to ensure that in the absence of liquid flow, machine gunners stop the pumping station and prevent “dry running”, and when water appears, put the equipment into action. The sensor obtained similar operating properties due to its design.

The device consists of a valve (“petal”), which is located in the flow part, and a reed switch. When water pressure arises, the reed valve begins to move, compressing the spring. At the same time, the magnet on the “petal” and the reed relay interact.

As a result, the contacts close, which activates the submersible or circulation pump. When there is no water and corresponding pressure in the system, the valve spring expands, moving the magnet to its original position - this causes the contacts to open and the equipment to stop.

A water flow sensor for a circulation or submersible pump is easy to install in an existing system; you just need to choose the right device, paying due attention to key parameters.

1.2 Main characteristics

The purchase of a water flow sensor should be approached carefully. We recommend focusing on the following characteristics of the device:

• material of the body and working components;
• operating pressure;
• coolant temperature range;
• operating conditions and protection class;
• thread diameter.

To understand the impact each of these factors has on operational features devices, we will consider them step by step. The material of the housing and operating components affect the reliability and durability of the sensor that is installed on the pump. It is desirable that the device be based on metals: stainless steel, aluminum or brass.

These materials are able to protect working elements from a powerful flow of water and hydraulic shock. Be sure to study the operating pressure level at which the sensor is capable of operating. For each circulation pump this value will be individual, so you need to calculate the appropriate parameter in advance.

There are devices that provide two levels of pump control: at the lower pressure limit of the system to turn it on and at the upper pressure limit in case of interruption or an unacceptably low level of water flow to turn off the pumping station.

A sensor with the possibility of such programming is considered optimal. When choosing equipment for controlling water flow, one cannot neglect such a parameter as the temperature range of the coolant.

Conditions for using devices may vary significantly. It’s one thing if you have to install a sensor in a heating system, where temperatures can reach 110°C, and quite another when the pump is used to turn on and supply cold water.

In the latter case, you can choose a device designed for a temperature range of 60-80°C. To ensure that the pump and purchased sensor remain operational for as long as possible, pay attention to the conditions under which the equipment should operate.

The instructions for the device must indicate the temperature level environment and protection class. The last criterion determines the loads that the sensor installed in the pump can withstand.

To produce the correct and precision installation You will have to pay attention not only to the permissible operating temperatures of the device, but also to the diameter of the connecting thread. Only with correct and high-quality joining of the elements can the effective functioning of the sensor be achieved after its preliminary installation and switching on.

1.3 About the device and characteristics (video)

2 Adjustment and connection of the sensor

The flow sensor, which is used to monitor the water level and pressure in the system, should be adjusted immediately after purchase. The process works as follows: the device is shipped with the contacts open and the calibration screw tightened.

After turning on the pump and reaching the optimal water level, the lamella moves in the direction of the liquid flow, which leads to the closure of the contacts. If the lamella does not start to move, this means that this level of water flow is not enough. If the device does not respond, you need to set a different value and perform the operation again.

There are a number of rules that will facilitate the installation of a flow sensor, the main one is that the device must be installed on a horizontal pipeline, regardless of the temperature of the water moving inside. In this case, you need to ensure that the lamella is positioned vertically.

The distance between the pipe and the device should be carefully measured - the minimum acceptable value is 55 mm. Using a threaded coupling, the sensor is connected to the drain pipeline, regardless of the water level inside.

The device must be oriented so that the arrows on its body correspond to the direction of water flow in the system. When high level coolant contamination is mounted in front of the sensor.

Taking good care of the equipment that supplies water significantly extends its service life and guarantees uninterrupted operation of the system. This requires not only timely inspection and proper care, but also equipping the pumps with a full set of protection devices. Preventing the possibility of a serious breakdown is much cheaper than repairing or buying a new unit. Do you agree?

Installing a water flow switch will protect the motor of both surface and deep-well pumping equipment. After all, most often when the motor burns out, it’s easier to buy new pump than to change it. We will tell you how this important protective device works, how to choose it and include it in an autonomous water supply.

The article provides valuable recommendations for installing devices to protect pumps from operating in “dry running” conditions. The technology of customization for individual requirements has been analyzed. For a better understanding of the considerable amount of information, photographs, diagrams, video reviews and manuals are attached.

In household water supply systems, the action of a pumping station without water quite often occurs and threatens an accident. This problem is called “dry running”.

As a rule, the liquid cools and lubricates the elements of the system, thereby ensuring its normal operation. Even short-term dry operation leads to deformation of individual parts, overheating and failure of the equipment motor. Negative consequences apply to both surface and deep-well pump models.

Dry running occurs for various reasons:

• incorrect choice of pump capacity;
• unsuccessful installation;
• violation of the integrity of the water pipe;
• low fluid pressure and lack of control over its level, for which they use;
• accumulated debris in the pumping pipe.

An automatic sensor is necessary in order to completely protect the device from the threats posed by lack of water. It measures, controls and maintains constant water flow parameters.

Pumping equipment equipped with a sensor has many advantages. It lasts longer, breaks down less often, and uses energy more economically. There are also relay models for boilers

The main purpose of the relay is to independently turn off the pumping station when the liquid flow is insufficient and turn it on after normalization of the indicators.

Design and operating principle

The sensor has a unique device, thanks to which it performs its direct functions. The most common modification is the paddle relay.

IN classic scheme The structure includes the following important elements:

• an inlet pipe that passes water through the device;
• valve (petal) located on the wall of the inner chamber;
• an isolated reed switch that opens and closes the power supply circuit;
• springs of a certain diameter with varying degrees of compression.

While the chamber is filled with liquid, the force of the flow begins to act on the valve, displacing it around its axis.

Magnet built-in with reverse side petal, comes close to the reed switch. As a result, the contacts close, turning on the pump.

The flow of water is understood as the speed of its physical movement, sufficient to turn on the relay. Reducing the speed to zero, resulting in a complete stop, returns the switch to its original position. When setting the response threshold, this parameter is set taking into account the conditions of use of the device

When the flow of fluid stops and the pressure in the system drops below normal, the compression of the spring weakens, returning the valve to its original position. Moving away, the magnetic element ceases to function, the contacts open and the pumping station stops.

Some modifications are equipped with a return magnet instead of springs. Judging by user reviews, they are less susceptible to minor pressure surges in the system.

Leaf relays are characterized by a large number of pros. Among them are a simple and unpretentious design, instant response, no delays between repeated responses, and the use of a precise trigger to start the equipment.

Depending on the constructive solution There are several other types of relays. These include rotary devices equipped with a paddle wheel rotating in a water flow. The speed of rotation of the blade in them is controlled touch sensors. If there is liquid in the pipe, the mechanism deflects, closing the contacts.

There is also a thermal relay that operates according to thermodynamic principles. The device compares the temperature set on the sensors with the temperature of the working medium in the system.

If there is flow, a thermal change is detected, after which the electrical contacts are connected to the pump. If there is no water movement, the microswitch disconnects the contacts. The models are characterized by high sensitivity, but they are quite expensive.

Device selection criteria

When choosing equipment that controls the force of water flow, you should carefully study it specifications.

Particular attention should be paid to the operating temperature and pressure range for which it is designed, the diameter of the threads and mounting holes, the protection class, and application nuances. It is also important to clarify what materials the product is made from.

Experts consider brass devices to be the most reliable and durable, of stainless steel, aluminum. These materials protect the structure from the critical consequences of frequent water supply systems phenomena – hydraulic shocks

When considering different modifications of the relay, it makes sense to purchase a version made of metal. The housing and working components of such devices are highly durable.

This fact allows the equipment long time withstand severe loads arising from significant fluid passing through the sensor.

The pressure value at which the relay operates must correspond to the power installed pump. The parameters of the water flow circulating through the pipeline depend on this characteristic.

It is advisable to choose a device with two springs that controls the operation of the pumping station according to certain lower and upper pressure marks.

The operating temperature range of the sensor directly indicates its possible area of ​​application. For example, models with a high limit temperature are designed for hot water supply circuits and heating systems. For pipelines with cold water A range of up to 60 degrees is quite sufficient

Another important criterion that deserves special mention is climatic conditions necessary for the operation of the product. It's about about the recommended air temperature and humidity level that the device needs to provide in order for it to operate at its best performance.

Maximum permissible loads for a specific device determines the protection class specified in the technical specifications.

When purchasing a flow sensor, you should check the thread diameter and the dimensions of the mounting holes in the equipment: they must fit perfectly with the pipeline elements. The correctness and accuracy of further installation, as well as the efficiency of the relay after installation, depend on this.

Trusted Instruments

Among the entire range of relays, the two models that are in approximately the same price category are in greatest demand - about $30. Let's take a closer look at their characteristics.

Genyo Lowara Genyo 8A

Development of a Polish company producing electronic equipment for control systems. Designed for use in domestic water supply systems.

Genyo allows you to provide automatic control pump: starts and stops based on actual water consumption, preventing any pressure fluctuations during operation. Also, the electric pump is protected from running “dry”

The main purpose is to control the pump and control the pressure in the pipes during operation. This sensor starts the pump when the water flow exceeds 1.6 liters per minute. It consumes 2.4 kW of electricity. Operating temperature range – from 5 to 60 degrees.

Grundfos UPA 120

Manufactured in factories in Romania and China. Maintains stable water supply in rooms equipped with individual systems water supply Prevents pumping units from idling.

Relay trademark Grundfos is equipped with a high protection class, allowing it to withstand almost any load. Its electricity consumption is about 2.2 kW

The device’s automation starts at a liquid flow rate of 1.5 liters in one minute. Boundary parameter of the covered temperature range- 60 degrees. The unit is manufactured in compact linear dimensions, significantly simplifying the installation process.

Liquid flow relays are installed for devices that require constant control and compliance with a certain operating mode. Often they are equipped with equipment at the production stage. However, there are also circumstances when a separate installation of the sensor is required.

Rules for installing relays in the system

Installing a safety device that detects the presence or absence of water flow in the system is a reasonable step in cases where it is not possible to be constantly present during the operation of the pumping equipment.

It is not required only in two cases:

1. Water is pumped from a large well with unlimited resources by a low-power pump.
2. It is possible to independently turn off the installation when the water level drops below the designated norm.

The device is installed on horizontal sections of the pipeline. In this case, you need to ensure that the membrane takes a stable vertical position.

The device is mounted to the drain pipeline using a threaded coupling. Usually a special socket is provided for this.

If the pumping equipment does not have a hole for mounting the sensor, you can replace it with a brass tee. In addition to the relay, a pressure gauge is connected to it, showing the current pressure in the network

Before you begin directly screwing the device, it is advisable to seal the threads well with flax or thread, sold in specialized departments.

It is better to wind it clockwise towards the end. This method of fastening increases the reliability of fixation.

In order not to damage the relay, you should screw it very carefully, slightly tightening it wrench. Optimal distance between the product and the pipeline - at least 55 mm

When installing a factory sensor, you need to focus on the arrow shown on the body. The direction indicated on it must coincide with the direction of flow of the liquid passing through the device.

If contaminated water is transported through the pipeline, it is recommended to install cleaning filters, placing them near the sensor. Such a move will ensure the correct operation of the product.

At the final stage installation work The dry running relay is connected to the electrical network:

• a wire core is screwed to the free ends of the two groups of contacts;
• a ground connection is attached to the sensor screw;
• the device is connected to the pump by connecting two devices with a regular wire in compliance.

After connecting to the network, all that remains is to check the functionality of the system. The fact that the device is ready for full operation will be indicated by an increase in pressure marks on the pressure gauge and the automatic shutdown of the pump when the limit value is exceeded.

Self-adjustment procedure

For adjustment, the sensor has special bolts. By loosening or tightening them, you can reduce or increase the compression force of the spring.

This sets the pressure level at which the device will operate.

Almost always, manufacturing companies produce equipment with adjusted settings. Despite this, sometimes additional self-adjustment is required

In most cases, setting up automatic equipment is not difficult.

It is advisable to adhere to the following algorithm:

• drain the liquid from the system until the pressure mark reaches zero;
• turn on pumping unit and slowly turn the water back on;
• record the flow pressure indicator when the pump is turned off with a sensor;
• start draining again and remember the indicators at which pump equipment will start working;
• open the relay and use the adjusting bolt to adjust the minimum level of compression of the larger spring required to activate the device and start the pump (more compression increases the degree of pressure, less - reduces it);
• in a similar way, adjust the compression force of a smaller spring mechanism, setting the limits of the maximum pressure, upon reaching which the relay measuring the water flow will turn off the pump.

Having completed all the described manipulations, you should make sure that the adjustments made are correct. To do this, the pipeline is filled with liquid and then drained, assessing the sensor’s response when the set values ​​are reached.

If the test result is unsatisfactory, the procedure is repeated.

Having insufficient experience and qualifications, it is better to seek help in adjustment from specialists. They will analyze the specific situation, take into account the technical characteristics of the equipment and select the most correct pressure level values

To ensure that the pipeline through which the liquid passes works properly and stably, regular annual checks of the flow sensors are carried out. If necessary, the operating parameters are adjusted.

Conclusions and useful video on the topic

Structure, components and operating principles:

The process of connecting a device in stages:

Learn more about how to adjust the trigger level in a relay:

A relay that controls the flow of water in the pipeline will significantly increase the ease of use of pumps and extend their service life for a long time. It is highly undesirable to neglect the installation of a safety device, since it not only automates the operation of the equipment, but also protects it to the maximum from possible problems that occur due to idling.

Do you want to install the flow switch yourself, but are a little confused about the instructions? Please ask your questions, and we and our website visitors will try to help you.

Or maybe you have successfully completed the installation and configuration of the device and want to give useful recommendations other newbies? Write your comments in the block below, add photos of the installation or setup process - your experience will be useful to many home craftsmen.

During the entire period of its operation. Installing a flow switch in the refrigeration system is mandatory, since its main function is to protect the chiller from an emergency situation: extremely small or complete absence of liquid flow through the evaporator. This is possible in the system only in one case - when the compressor is not working refrigeration machine.

Flow switch - a sensor (microswitch, differential pressure switch, etc.) signaling to the chiller controller that in the coolant circulation system there is a physical flow of liquid through the chiller evaporator, and the flow rate through the evaporator corresponds to the nominal calculated value for the selected operating parameters of the chiller in the refrigeration system.

In practice, flow switches are used various types: mechanical and differential relays, differential pressure sensors, etc. The purpose of the devices is one - to signal to the chiller controller about the normal flow of liquid through the evaporator. This determines the installation location flow switch- on the pipeline lines of the circulation circuit near the evaporator, as shown in Fig. 7.

It is most advisable to install a flow switch on the pipeline at the outlet of the evaporator. A straight section of pipe with a length of at least 10 gauges is selected and a flow switch is installed in the center of this section. It is not allowed to install a flow switch near pipe bends, shut-off valves or valves, control fittings.

The flow switch housing is mounted in a vertical position, and the direction of the arrow on the flow switch housing must coincide with the direction of coolant flow. When installing a flow switch, it is necessary to ensure that the contact group of the relay is protected from dirt and moisture entering the housing. It is allowed to install a mechanical flow switch on straight vertical sections of pipes, but only if the direction of movement of the coolant is from bottom to top.

The simplest and cheapest flow relays are mechanical relays, the principle of which is to close the microswitch contacts when turning the sensitive plate (“feather”) located in the flow of moving liquid. The length of the plate is selected depending on the diameter of the line into which the flow switch is inserted.

The choice of plate length is a crucial point when installing a flow switch, since it determines its sensitivity. Thus, with short plate lengths, the contacts of the flow switch installed in the pipeline large diameter, will not close even at normal flow rates, as shown in Fig. 8.

For large diameter pipelines, it is recommended to place several plates of shorter length under the sensitive plate (a kind of “spring”), otherwise the relay may quickly fail due to breakage of the plate at the sealing site. Figure 9 shows typical practical errors when installing mechanical flow switches:

In the first case, when installing the flow switch, they “forgot” to install the plate; in the second case, the long plate “clings” to the pipe as it turns. In the third case, the length of the plate does not correspond to the diameter of the pipeline, so the plate was installed in some arbitrary position when installing the flow switch; in the fourth case, the arrow on the flow switch body does not correspond to the direction of flow in the line.

The closure of the flow switch contacts when the required calculated value of liquid flow in the line is reached is regulated by a screw in the relay body when adjusting the hydraulic circuit during commissioning (see Fig. 10). If for some reason the flow rate in the main line, considered in the evaporator, becomes less (G„2

Chillers, as a rule, are equipped with two sequentially connected stages of protection for the absence or non-compliance with the calculated value of liquid flow through the evaporator. Fig. 11, as an example, shows a fragment of an electric DAIKIN with a single-screw compressor.

The first stage consists of “dry” pump contacts (S9L), which close when power is supplied to the pump group of the circulation circuit. The signal to turn on the pump group is sent to the controller, but this is not enough to confirm the normal flow of liquid through the chiller evaporator. For this purpose, a flow switch is used, the closure of the contacts (S8L) of which indicates that the flow through the evaporator has reached the required value. Only after this does the countdown of the chiller compressor start timer begin, and after it is reset to zero, the compressor actually starts.

If, for some reason, the liquid flow through the evaporator decreases or stops altogether, the protection chain opens and the chiller compressor stops emergency. Modern chiller controllers record an emergency, so the cause of the emergency stop (flow switch) can be easily identified.

If necessary, the chain of protection (Fig. 11) along the flow of liquid through the heat exchangers of the chiller can be expanded. So, with a water-cooled condenser, this chain includes in series the “dry” contacts of the pump group and the flow switch on the side.

When installing refrigeration station equipment, it is also necessary to take into account the electrical connection features of the chiller and pump group. It is recommended to provide power supply separately: connecting the pump group from the chiller is not allowed. When starting a refrigeration station, the pump group is always turned on first, then the chiller.

The nominal parameters of the chiller (cooling capacity, power consumption and flow through the evaporator) are given in the technical data at an ambient temperature of +35°C; The coolant of the circulation circuit is water; water temperature at the evaporator outlet + 7°C; water at the inlet/outlet of the evaporator 5K.

From the conditions optimal performance heat exchanger - evaporator (heat exchange and hydraulic characteristics of the unit), an operating temperature difference is allowed in a narrow range from 3 to 8 K. In accordance with the above, the following are distinguished:

• Minimum coolant flow in circulation system, corresponding to the maximum temperature difference across the evaporator - 8K. This value is lower threshold according to the flow rate in the evaporator circulation system, below which the manufacturer does not recommend operation of the device - at such low flow rates, freezing of the evaporator channels is possible.
• The nominal coolant flow rate in the circulation system, corresponding to the standard temperature difference on the evaporator is 5K, the coolant is water. This value characterizes the stable operation of the chiller.
• Maximum flow coolant in the circulation system, corresponding to the minimum temperature difference across the evaporator - 3K. This value is the upper limit for the flow rate in the evaporator circulation system. A further increase in flow rate is impractical due to the deterioration of the evaporator characteristics due to an increase in its hydraulic resistance.
• The calculated coolant flow through the chiller evaporator, corresponding to the temperature difference on the evaporator selected when designing the refrigeration system, the selected chiller parameters when selecting equipment, and the selected type of coolant in the circulation circuit. For standard conditions, the calculated flow rate corresponds to the nominal value.