Hydro arrow for heating: principle of operation and purpose

Recommendation points

• How does a hydraulic arrow work
• What capabilities are attributed to the hydroseparator
• Real scope
• Connection diagram and installation
• About separation headers

The hydraulic divider is a device covered with many myths. To figure out what tasks the hydrostatic gun is really capable of coping with, and which of its properties are just unfounded statements by marketers, we propose to consider in detail the principle of operation of this unit and its purpose.

How does a hydraulic arrow work

The hydraulic arrow is a flask with an automatic air vent installed in the upper part. On the side surface of the body, nozzles are cut in for connecting the main heating pipes. Inside the hydraulic arrow is absolutely hollow, in the lower part a threaded branch pipe can be cut to install a ball valve, the purpose of which is to drain the settled sludge from the bottom of the separator.

Essentially, a hydraulic switch is a shunt that short-circuits the supply and return flows. The purpose of such a shunt is to equalize the temperature of the heat carrier, as well as its flow in the generating and distribution parts of the hydraulic heating system. To obtain a real effect from a hydroseparator, a careful calculation of its internal volume and points of connection of the pipes is required. However, most of the devices on the market are manufactured in series without adaptation to a specific heating system..

It is often believed that additional elements must be present in the flask cavity, such as flow dividers or meshes for filtering mechanical impurities or separating dissolved oxygen. In reality, such modernization methods do not demonstrate any significant efficiency, and even vice versa: for example, if the grid is clogged, the hydraulic arrow completely stops working, and with it the entire heating system.

What capabilities are attributed to the hydroseparator

Among heat engineers, there are diametrically opposed opinions about the need to install hydraulic guns in heating systems. The statements of hydraulic equipment manufacturers, promising an increase in the flexibility of setting operating modes, an increase in the efficiency and efficiency of heat transfer, add fuel to the fire. To separate the grain from the chaff, let’s first consider the absolutely groundless claims about the “outstanding” capabilities of hydraulic separators..

The efficiency of the boiler plant does not depend in any way on the devices installed after the boiler connection pipes. The useful effect of the boiler is entirely contained in the converting capacity, that is, in the percentage of the heat released by the generator to the heat absorbed by the coolant. No special piping methods can increase the efficiency, it depends only on the surface area of ​​the heat exchanger and the correct choice of the coolant circulation rate.

Multi-mode, which is supposedly provided by the installation of a hydraulic arrow, is also an absolute myth. The essence of the promises boils down to the fact that in the presence of a hydraulic arrow, it is possible to implement three options for the flow ratio in the generator and consumer parts. The first one is the absolute equalization of the flow rate, which in practice is just possible only in the absence of shunting and only one circuit in the system. The second option, in which the flow rate in the circuits is greater than through the boiler, supposedly provides increased savings, however, in this mode, a supercooled coolant inevitably enters the heat exchanger via the return flow, which generates a number of negative effects: fogging of the internal surfaces of the combustion chamber or temperature shock.

There are also a number of arguments, each of which represents an incoherent set of terms, but inherently does not reflect anything specific. These include an increase in hydrodynamic stability, an increase in the service life of equipment, control over the temperature distribution and others like them. You can also find the statement that the hydraulic separator allows you to stabilize the balance of the hydraulic system, which in practice turns out to be exactly the opposite. If, in the absence of a hydraulic arrow, the reaction of the system to a change in flow in any of its parts is inevitable, then in the presence of a separator it is also absolutely unpredictable.

Real scope

However, a thermo-hydraulic separator is far from useless. This is a hydraulic engineering device and its principle of operation is described in sufficient detail in special literature. Hydrostrelka has a well-defined, albeit rather narrow, scope.

The most important benefit of a hydraulic separator is the ability to coordinate the operation of several circulation pumps in the generator and consumer parts of the system. It often happens that circuits connected to a common manifold unit are supplied with pumps whose performance differs by 2 or more times. At the same time, the most powerful pump creates a pressure difference so high that the intake of the coolant by the rest of the circulation devices is impossible. Several decades ago, this problem was solved by the so-called washer – artificially lowering the flow in consumer circuits by welding metal plates with different hole diameters into the pipe. The hydraulic arrow shunts the supply and return lines, due to which the vacuum and excess pressure in them are leveled.

The second special case is the excess boiler performance in relation to the consumption of the distribution circuits. This situation is typical for systems in which a number of consumers do not work on a permanent basis. For example, an indirect heating boiler, a pool heat exchanger and heating circuits of buildings that are heated only from time to time can be linked to general hydraulics. The installation of a hydraulic arrow in such systems allows maintaining the nominal boiler power and circulation rate all the time, while the excess heated coolant flows back into the boiler. When an additional consumer is turned on, the difference in flow rates decreases and the surplus is no longer sent to the heat exchanger, but to the open circuit.

The hydrostatic gun can also serve as a collector of the generator part when coordinating the operation of two boilers, especially if their power is significantly different. An additional effect of the operation of the hydraulic arrow can be called the protection of the boiler from temperature shock, but for this, the flow rate in the generator section must exceed the flow rate in the consumer network by at least 20%. The latter is achieved by installing pumps of appropriate capacity..

Connection diagram and installation

The hydraulic switch has a connection diagram as simple as its own device. Most of the rules relate not so much to the connection as to the calculation of the bandwidth and the pinout. Nevertheless, knowledge of the complete information will allow the installation to be carried out correctly, as well as to make sure that the selected hydraulic arrow is suitable for its installation in a specific heating system.

The first thing that needs to be clearly understood is that the hydraulic arrow will work only in heating systems with forced circulation. In this case, there should be at least two pumps in the system: one in the circuit of the generating part, and at least one in the consumer. Under other conditions, the hydraulic separator will act as a shunt with zero resistance and, accordingly, will short-circuit the entire system.

An example of a water arrow connection diagram: 1 – heating boiler; 2 – boiler safety group; 3 – expansion tank; 4 – circulation pump; 5 – hydraulic separator; 6 – automatic air vent; 7 – shut-off valves; 8 – drain valve; 9 – circuit No. 1 indirect heating boiler; 10 – circuit No. 2 heating radiators; 11 – three-way valve with an electric drive; 12 – contour No. 3 warm floor

The next aspect is the size of the hydraulic arrow, the diameter and the location of the leads. In the general case, the diameter of the flask is determined based on the largest design flow in the line. The maximum can be taken to be the flow rate of the coolant either in the generating or in the consumer part of the heating system according to the data of the hydraulic calculation. The dependence of the diameter of the separator flask on the flow is described by the ratio of the flow rate to the flow rate of the coolant through the flask. The last parameter is fixed and, depending on the capacity of the boiler plant, can vary from 0.1 to 0.25 m / s. The quotient obtained when calculating the specified ratio must be multiplied by a correction factor of 18.8.

The diameter of the connection pipes must be 1/3 of the diameter of the flask. In this case, the inlet pipes are located from the top and bottom of the flask, as well as from each other at a distance equal to the diameter of the flask. In turn, the outlet nozzles are positioned so that their axes are offset relative to the bushing axes by two proper diameters. The described regularities determine the total height of the body of the hydraulic arrow.

The hydraulic arrow is connected to the direct and return main pipelines of the boiler or several boilers. Of course, when connecting the hydraulic arrow, there should not be a hint of a narrowing of the conditional passage. This rule forces to use pipes with a very significant nominal bore in the boiler piping and when connecting the collector, which somewhat complicates the issue of optimizing the layout of the boiler room equipment and increases the material consumption of the piping.

About separation headers

Finally, let’s briefly touch on the topic of multi-outlet hydrostops, also known as sepkolls. In essence, it is a collector group in which the supply and return splitter are combined by a separator. Devices of this kind are extremely useful when coordinating the operation of several heating circuits with different flow rates and coolant temperatures..

The vertical separation manifold allows for a temperature gradient in the outlet nozzles by mixing portions of the coolant. This makes it possible to directly connect, for example, an indirect heating boiler, a radiator group and underfloor heating loops without a mixing group: the temperature difference between adjacent sepcoll outlets will naturally be maintained within 10-15 ° C, depending on the circulation mode. However, it should be remembered that such an effect is possible only if the return pipe of the generating part is located above the return outlets of consumers..

As a result, we will give an important recommendation. Most domestic heating systems up to 100 kW do not require a low loss header. A much more correct solution would be to select the capacity of the circulation pumps and coordinate their operation, and to protect the boiler from thermal shock, connect the mains with a bypass tube. If the design or installation organization insists on the installation of a hydraulic arrow, this decision must necessarily be justified technologically.