What is a hydraulic arrow (low loss header) in the heating system

Designing your own heating system is far from easy. Even if the installers "plan" it, you need to be aware of many nuances. Firstly, to monitor their work, and secondly, to assess the necessity and feasibility of their proposals. For example, in recent years, a water gun for heating has been strongly promoted. This is a small addition, the installation of which results in a considerable amount. In some cases it is very useful, in others it can be easily done without it.

What is a hydraulic arrow and where is it installed

The correct name for this device is hydraulic pointer or hydraulic separator. It is a piece of round or square pipe with welded pipes. There is usually nothing inside. In some cases, there may be two nets. One (above) for better "discharge" of air bubbles, the second (below) for filtering out impurities.

Examples of industrial-made hydraulic shooters

In the heating system, a hydraulic arrow is placed between the boiler and consumers - heating circuits. It can be located both horizontally and vertically. More often they are placed vertically. With this arrangement, an automatic air vent is installed in the upper part, and a shut-off valve at the bottom. Some of the water with accumulated dirt is periodically drained through the tap.

Where is a hydraulic separator installed in the heating system

That is, it turns out that a vertically placed hydraulic separator, simultaneously with its main functions, removes air and makes it possible to remove sludge.

Purpose and principle of operation

A water gun is needed for branched systems in which several pumps are installed. It provides the required coolant flow for all pumps, regardless of their performance. That is, in other words, it serves to hydraulically decouple the heating system pumps. Therefore, this device is also called - a hydraulic separator or a hydraulic separator.

Schematic representation of the hydraulic arrow and its place in the heating system

A hydraulic arrow is installed if the system provides several pumps: one on the boiler circuit, the rest on the heating circuits (radiators, water floor heating, indirect heating boiler). For correct operation, their performance is selected so that the boiler pump can pump a little more coolant (by 10-20%) than is required for the rest of the system.

Why do I need a water gun for heating? Let's take an example. In a heating system with several pumps, they often have different capacities. It often happens that one pump is many times more powerful. All pumps have to be installed side by side - in the manifold unit, where they are hydraulically connected. When a powerful pump is turned on at full power, all other circuits are left without a coolant. This happens all the time. To avoid such situations, a hydraulic arrow is installed in the heating system. The second way is to spread the pumps over a long distance.

Operating modes

Theoretically, three modes of operation of the heating system with a hydraulic arrow are possible. They are shown in the figure below. The first is when the boiler pump pumps exactly the same amount of coolant as the entire heating system requires. This is an ideal situation that is very rare in real life. Let us explain why.Modern heating adjusts the work according to the temperature of the heating medium or the temperature in the room. Imagine that everything is perfectly calculated, the valves are turned on and after adjustment, equality is achieved. But after a while, the parameters of the boiler or one of the heating circuits will change. The equipment will adapt to the situation, and performance equality will be violated. So this regime can last for a few minutes (or even less).

Possible operating modes of the heating system with a hydraulic separator

The second mode of operation of the hydraulic arrow is when the flow rate of the heating circuits is greater than the power of the boiler pump (middle figure). This situation is dangerous for the system and should not be allowed. It is possible if the pumps are selected incorrectly. Rather, the boiler pump has too low capacity. In this case, in order to ensure the required flow rate, the coolant from the return flow will be supplied to the circuits together with the heated coolant from the boiler. That is, at the outlet of the boiler, for example, 80 ° C, in the circuit after adding cold water, for example, 65 ° C (the actual temperature depends on the flow deficit). Having passed through the heating devices, the coolant temperature drops by 20-25 ° С. That is, the temperature of the coolant supplied to the boiler will be 45 ° C at best. If we compare with the output - 80 ° C, then the delta of temperatures is too large for a conventional boiler (not condensing). This mode of operation is not normal and the boiler will quickly fail.

The third mode of operation is when the boiler pump delivers more heated coolant than the heating circuits require (right figure). In this case, part of the heated coolant is returned back to the boiler. As a result, the temperature of the incoming heat carrier rises, it works in a gentle mode. This is the normal operating mode of the heating system with a hydraulic arrow.

When a water gun is needed

A water gun for heating is needed 100% if several boilers operating in a cascade will be in the system. Moreover, they must work simultaneously (at least most of the time). Here, for correct operation, the hydraulic separator is the best way out.

In the presence of two simultaneously operating boilers (in a cascade), a hydraulic arrow is the best option

Another water gun for heating can be useful for boilers with a cast iron heat exchanger. In the tank of the hydraulic separator, warm and cold water is constantly mixed. This reduces the delta temperature at the outlet and inlet of the boiler. For a cast iron heat exchanger, this is a blessing. But a bypass with a three-way adjustable valve will cope with the same task and will cost much less. So, even for cast iron boilers in small heating systems, with approximately the same flow rate, it is quite possible to do without connecting a hydraulic arrow.

When can I put

If there is only one pump in the heating system - on the boiler, the hydraulic arrow is not needed at all. You can also do without if one or two pumps are installed on the circuits. Such a system can be balanced using control valves. When is the installation of a hydraulic arrow justified? When such conditions are available:

• There are three or more circuits, all of very different power (different circuit volume, different temperatures are required). In this case, even with ideally accurate selection of pumps and calculation of parameters, there is a possibility of unstable system operation. For example, a situation is often encountered when the radiators get cold when the underfloor heating pump is turned on. In this case, a hydraulic disconnection of the pumps is needed and therefore a hydraulic arrow is installed.
• In addition to radiators, there is a water-heated floor that heats large areas. Yes, it can be connected through a manifold and a mixing unit, but it can make the boiler pump work in extreme mode. If your heating pumps often burn, most likely you need to install a hydraulic arrow.
• In a system of medium or large volume (with two or more pumps), you are going to install automatic control equipment - according to the temperature of the coolant or according to the air temperature. At the same time, you do not want / cannot regulate the system manually (with taps).

An example of a heating system with a hydraulic arrow

In the first case, a hydraulic break is most likely needed, in the second, you should think about installing it. Why just think? Because this is a big expense. And it's not just the cost of the hydraulic arrow. It costs about $ 300. We'll have to install additional equipment. At a minimum, collectors are needed at the inlet and outlet, pumps for each circuit (with a small system, you can do without a hydraulic arrow), as well as a pump speed control unit, since they cannot be controlled through the boiler. Together with the payment for the installation of equipment, this "appendage" translates into about two thousand dollars. Really a lot.

Why is this equipment installed then? Because with a hydraulic arrow, heating works more stable, it does not require constant adjustment of the coolant flow in the circuits. If you ask the owners of cottages whose heating is done without a hydraulic separator, they will tell you that you often have to reconfigure the system - turn the valves, adjusting the coolant flows in the circuits. This is typical if different heating elements are used. For example, on the ground floor there is underfloor heating, radiators on two floors, heated utility rooms in which a minimum temperature must be maintained (garage, for example). If you are supposed to have approximately the same system, and the prospect of "tuning" does not suit you, you can put a hydraulic arrow for heating. If it is present, as much coolant goes into each circuit as it requires at the moment and does not in any way depend on the operating parameters of a number of pumps of other circuits.

How to choose parameters

The hydraulic separator is selected taking into account the maximum possible flow rate of the heat carrier. The fact is that at a high speed of fluid movement through the pipes, it begins to make noise. To avoid this effect, the maximum speed is taken equal to 0.2 m / s.

Parameters required for the hydraulic separator

According to the maximum flow of the coolant

To calculate the diameter of the hydraulic arrow using this method, the only thing you need to know is the maximum coolant flow that is possible in the system and the diameter of the nozzles. With the pipes, everything is simple - you know which pipe you will make the wiring. We know the maximum flow that the boiler can provide (there is in the technical specifications), and the flow rate along the circuits depends on their size / volume and is determined when selecting circuit pumps. The flow rate for all circuits is added up and compared with the power of the boiler pump. A large value is substituted into the formula for calculating the volume of the hydraulic arrow.

Formula for calculating the diameter of a low loss header for a heating system depending on the maximum flow of the heating medium

Let's give an example. Let the maximum flow rate in the system be 7.6 cubic meters per hour. The permissible maximum speed is taken as standard - 0.2 m / s, the diameter of the nozzles is 6.3 cm (pipes by 2.5 inches). In this case, we get: 18.9 * √ 7.6 / 0.2 = 18.9 * √38 = 18.9 * 6.16 = 116.424 mm. If rounded off, we get that the diameter of the hydraulic arrow should be 116 mm.

According to the maximum boiler power

The second way is the selection of the hydraulic arrow according to the boiler power. The estimate will be rough, but you can trust it. You will need the power of the boiler and the temperature difference between the coolant in the supply and return pipelines.

Calculation of the hydraulic arrow by boiler power

The calculation is also simple. Let the maximum boiler power be 50 kW, the temperature delta is 10 ° C, the diameters of the pipes are the same - 6.3 cm.Substituting the numbers, we get - 18.9 * √ 50 / 0.2 * 10 = 18.9 * √ 25 = 18.9 * 5 = 94.5 mm. Rounding off, we get the diameter of the hydraulic arrow 95 mm.

How to find the length of the hydraulic arrow

We decided on the diameter of the hydraulic divider for heating, but you also need to know the length. It is selected depending on the diameter of the connected pipes. There are two types of hydraulic arrows for heating - with taps located opposite each other and with alternating pipes (located with a shift relative to each other).

Determine the length of the hydraulic arrow from a round pipe

It is easy to calculate the length in this case - in the first case it is 12d, in the second - 13d. For medium systems, the diameter can be selected depending on the nozzles - 3 * d. As you can see, nothing complicated. You can calculate it yourself.

Buy or do it yourself?

As they said, a ready-made hydraulic gun for heating costs a lot - $ 200-300, depending on the manufacturer. To reduce costs, there is a natural desire to do it yourself. If you know how to cook, no problem - you bought the materials and made it. But at the same time, the following points must be taken into account:

• The thread on the grips must be well cut and symmetrical.
• The walls of the bends are of the same thickness.

The quality of a homemade product may not be very good

It seems obvious things. But you will be surprised how difficult it is to find four normal squeegees with normally made threads. Further, all welds must be of high quality - the system will work under pressure. The bends are welded strictly perpendicular to the surface, at the required distance. In general, this is not an easy task.

If you yourself use a welding machine do not know how, you have to look for an artist. It is not at all easy to find him: either they ask dearly for services, or the quality of work, to put it mildly, is "not very good." In general, many people decide to buy a hydraulic arrow, despite the considerable cost. Moreover, in recent years, domestic manufacturers are doing no worse, but much cheaper.