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Designing your own heating system is far from easy. Even if its installers “plan” it, you need to be aware of many nuances. Firstly, to control their work, and secondly, to assess the necessity and expediency of their proposals. For example, in recent years, a hydraulic arrow for heating has been intensively 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 dispensed with.
What is a hydraulic gun and where is it installed
The correct name for this device is a hydraulic arrow or hydraulic separator. It is a piece of a round or square pipe with welded nozzles. Usually there is nothing inside. In some cases, there may be two grids. One (above) for a better “discharge” of air bubbles, the second (below) for screening out contaminants.
In the heating system, the hydraulic arrow is placed between the boiler and consumers – heating circuits. Can be positioned both horizontally and vertically. Most often placed vertically. With this arrangement, an automatic air vent is placed in the upper part, and a stopcock is placed below. Some of the water with accumulated dirt is periodically drained through the tap.
That is, it turns out that a vertically placed hydraulic separator, simultaneously with the main functions, removes air and makes it possible to remove sludge.
Purpose and principle of operation
A hydraulic 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 for hydraulic decoupling of the heating system pumps. Therefore, this device is also called a hydraulic separator or hydraulic separator.
A hydraulic arrow is installed if the system has 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 (10-20%) than is required for the rest of the system.
Why do you need a hydraulic arrow for heating? Let’s look at an example. In a heating system with several pumps, they often have different capacities. Often it turns out that one pump is many times more powerful. All pumps have to be installed side by side – in the collector unit, where they are hydraulically connected. When the powerful pump is turned on at full power, all other circuits are left without coolant. This happens all the time. To avoid such situations, they put a hydraulic arrow in the heating system. The second way is to spread the pumps over a long distance.
Modes of operation
Theoretically, there are three possible modes of operation of the heating system with a hydraulic arrow. 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’s explain why. Modern heating adjusts the work according to the temperature of the coolant or the temperature in the room. Let’s imagine that everything was perfectly calculated, the valves were tightened, and after the adjustment, equality was achieved. But after a while, the operating parameters of the boiler or one of the heating circuits will change. The equipment will adapt to the situation, and the equality of performance will be violated. So this mode can exist for a few minutes (or even less).
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 little capacity. In this case, to ensure the required flow rate, the heating medium from the return 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, after mixing cold water, for example, 65°C goes into the circuit (the actual temperature depends on the flow deficit). After passing through the heating devices, the temperature of the coolant drops by 20-25°C. That is, the temperature of the heat carrier supplied to the boiler will be at best 45°C. Compared to the output – 80 ° C, then the temperature delta is too large for a conventional (non-condensing) boiler. This mode of operation is not normal and the boiler will quickly fail.
The third mode of operation is when the boiler pump supplies more heated coolant than the heating circuits require (right figure). In this case, part of the heated coolant is returned to the boiler. As a result, the temperature of the incoming coolant rises, it works in a sparing mode. This is the normal mode of operation of the heating system with a hydraulic arrow.
When a hydraulic gun is needed
A hydraulic arrow for heating is 100% needed if the system has several boilers operating in a cascade. Moreover, they must work simultaneously (at least most of the time). Here, for correct operation, a hydraulic separator is the best way out.
Another hydraulic arrow for heating can be useful for boilers with a cast-iron heat exchanger. In the tank of the hydraulic separator, there is a constant mixing of warm and cold water. This reduces the temperature delta at the outlet and inlet of the boiler. For a cast-iron heat exchanger, this is a boon. But a bypass with a three-way adjustable valve will cope with the same task and it 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 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 gun justified? When the conditions are:
- There are three or more circuits, all of very different capacities (different volume of the circuit, different temperatures are required). In this case, even with perfectly accurate selection of pumps and calculation of parameters, there is a possibility of unstable operation of the system. For example, a situation often occurs when, when the floor heating pump is turned on, the radiators freeze. In this case, hydraulic decoupling 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, you most likely need to install a hydraulic gun.
- 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 air temperature. At the same time, you do not want / cannot regulate the system manually (with taps).
In the first case, hydraulic decoupling is most likely needed, in the second, it is worth thinking about installing it. Why only think? Because it’s a big expense. And it’s not just the cost of the water gun. It costs about $300. You will have to install additional equipment. At a minimum, you need collectors 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 can no longer be controlled through the boiler. In total, with the payment for the installation of equipment, this “appendage” translates into about two thousand dollars. Indeed a lot.
Why then put this equipment? 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 first floor there is a warm floor, radiators on two floors, heated utility rooms in which it is necessary to maintain a minimum temperature (garage, for example). If you are supposed to have approximately the same system, and the prospect of “tuning” does not suit you, you can install a hydraulic arrow for heating. If it is present, each circuit receives as much coolant as it requires at the moment and in no way depends on the operating parameters of pumps operating nearby in other circuits.
How to choose parameters
The hydraulic separator is selected taking into account the maximum possible flow rate of the coolant. The fact is that at a high speed of movement of the liquid through the pipes, it begins to make noise. To avoid this effect, the maximum speed is assumed to be 0,2 m/s.
According to the maximum coolant flow
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 branch pipes, everything is simple – you know which pipe you will do the wiring. We know the maximum flow that the boiler can provide (it is in the technical specifications), and the flow rate for the circuits depends on their size / volume and is determined when selecting the circuit pumps. The flow rate for all circuits is added up, compared with the power of the boiler pump. A large value is substituted into the formula for calculating the volume of the hydraulic gun.
Let’s take 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 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 we round it up, we get that the diameter of the hydraulic arrow should be 116 mm.
According to the maximum power of the boiler
The second method is the selection of a hydraulic arrow according to the power of the boiler. The estimate will be approximate, but it can be trusted. You will need the power of the boiler and the temperature difference of the coolant in the supply and return pipelines.
The calculation is also easy. Let the maximum power of the boiler be 50 kW, the temperature delta be 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, we get the diameter of the hydraulic arrow 95 mm.
How to find the length of a water gun
We decided on the diameter of the hydraulic separator for heating, but we also need to know the length. It is selected depending on the diameter of the connected nozzles. There are two types of hydraulic arrows for heating – with outlets located one opposite the other and with alternating pipes (they are located offset one relative to the other).
Calculating the length in this case is easy – in the first case it is 12d, in the second – 13d. For medium systems, you can choose the diameter depending on the nozzles – 3 * d. As you can see, nothing complicated. You can calculate on your own.
Buy or DIY?
As they said, a ready-made hydraulic arrow 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 did it. However, the following points must be taken into account:
- The carving on the sleds should be well cut and symmetrical.
- The walls of the outlets are of the same thickness.
Like obvious things. But you will be surprised how difficult it is to find four normal spurs with a normally made carving. Further, all welds must be of high quality – the system will work under pressure. The shanks are welded strictly perpendicular to the surface, at the right distance. In general, this is not such an easy task.
If you yourself do not know how to use a welding machine, you will have to look for a contractor. Finding him is not at all easy: either they ask for expensive services, or the quality of work, to put it mildly, is “not very good”. In general, many people decide to buy a water gun, despite the considerable cost. Moreover, recently, domestic manufacturers do not worse, but much cheaper.