- Rules for refueling a heat transfer fluid
- Where does air collect
- Pressure and circulation to help
- Open and closed systems – are there any differences
- Bleeding air from radiators
- The real problem: air in the pump and heat exchanger
- Bleed fittings
Airing a water heating system is an unpleasant incident that is rather difficult to foresee. You need to get rid of air congestion as soon as possible, so today we will tell you about the most vulnerable places and suggest methods for quickly eliminating the problem.
Rules for refueling a heat transfer fluid
If the heating system is constantly filled with water, the formation of air, or more correctly, gas jams in it, is possible only in the course of fairly specific processes. In most cases, airing of heating occurs precisely during the process of pumping the coolant, therefore, the power supply of the system must be performed in compliance with a number of rules.
The water supply pipe must be cut in at the lowest point of the system, usually this is the return section right next to the boiler or additional branches of the manifold assemblies. It is desirable that a valve be installed as a shut-off valve, and not a ball valve. This is due to the fact that water needs to be supplied under a small pressure, and the valve helps in regulating the flow as best as possible.
Entering the piping system, water will squeeze out air and for this you need to provide an outlet pipe. It must be located at the highest point in the system and mounted vertically. It is good if after the tap a fitting with a hose is packed, the end of which is lowered into a bucket of water placed on the floor. Then the signal about the end of the feeding will be the cessation of the formation of air bubbles squeezed out of the system..
Before draining water from the system, it is recommended to shut off all looped sections: the circulation pump, closed expansion tank and radiators. If they remain filled during repair work, this will slow down the corrosion of metal surfaces and eliminate the formation of plugs during the filling of the system..
Where does air collect
The appearance of air jams is often unpredictable and even well-designed systems are guilty of this. If parts of pipes or radiators do not heat up properly, this is due to air obstructing circulation. Another reason could be a clogged system.
Air is lighter than water and therefore collects at the highest point of the system or a separate section of it. A typical example is a forced-circulation system radiator without a top inlet. Strictly speaking, air never completely escapes from them, but its insignificant residue does not interfere with the duct and does not form noise.
Likewise, air locks can form in any other local elevation and in areas whose inlets are located below the plane of the pipes. As another example, we give U-shaped linear expansion joints. They should, if possible, bend downward, if not possible, equip them with a drain valve at the highest point.
Pressure and circulation to help
The formation of so-called counter-slopes is quite difficult to control when installing pipes. Even a small difference in levels can cause air blockage, complete or partial. It is easier to cope with such phenomena, the more intensively the coolant circulates inside the system..
Heating system with natural circulation: 1 – boiler; 2 – expansion tank; 3 – heating radiators
For example: sections of heating mains of the city heating system above roads and pedestrian zones, most likely, should remain clogged with air, but the water still circulates in them. This happens because of a pressure of 6-8 atm and a flow rate of the order of 1.5-2 m / s. A stormy stream of water carries away air bubbles with it, allowing them to reach the highest point, and the cork that remains is compressed by pressure to a tiny size.
Of course, it is unrealistic to achieve such operating parameters in domestic systems, but it is quite possible to turn on the circulation pump at maximum speed and temporarily increase the pressure in the system. This will facilitate the release of the remaining air, but the process will be quite sluggish, for several hours..
Open and closed systems – are there any differences
It will not be possible to use the compressibility of gases in open systems. This is the main difference and the main reason why pipelines of gravity systems are carefully designed..
If the formation of air in the local area occurs constantly and it is impossible to get rid of the active circulation and high pressure from the plug, the most correct solution would be to insert an overhead clamp at the highest point of the airborne area. This can be done without even merging the system. It is enough to pack the tap on the collar and close it immediately after the hole is drilled..
Insert of the overhead clamp
Closed systems with overpressure are distinguished by the simplest scheme for detecting air locks. The fact is that the compressibility of the air does not allow the system to gain a sufficiently high pressure during heating. The pressure gauge behaves as if a closed expansion tank is installed in the system with a capacity 3-4 times larger than the required one, the pressure increase is no more than 20% of the passport value.
Bleeding air from radiators
The formation of air pockets can appear even if not the entire system has been drained, but only a separate section of it, for example, a radiator. In this case, filling with water must be carried out in the following sequence:
- Loosen the top inlet fitting or open the bleed cock for unobstructed air outlet.
- Open the bottom tap and power the radiator until the exhaust air is replaced by water.
- Pack the top fitting and open the top supply valve.
In addition, all radiators of closed systems, as well as systems with lower wiring, must be supplied with Mayevsky cranes without fail. It is through them that the main volume of air is bleed off when refueling, since the upper radiator outlet is nothing more than the highest point of such a system.
Air removal using a Mayevsky crane
Please note that aluminum radiators can in some special cases serve as a source of gas for plugs. The fact is that with a high content of dissolved ions in water and the presence of electrical emission, aluminum quickly corrodes, releasing hydrogen in a significant volume. If you are faced with an implicit source of gas formation, exclude any contact of electrical equipment with the system and ground its metal parts.
The real problem: air in the pump and heat exchanger
There are situations when air locks not only block the fluid flow, but also threaten the failure of expensive system elements. This primarily applies to the circulation pump, which burns out from strong overheating, since water cannot cool the rotor. The main sign of an air pump is a complete lack of circulation in the system, determined by the lack of rapid heating of the supply pipe.
Bleeding air from the circulation pump is done by unscrewing the adjusting screw in the front of the housing. Be careful, as a significant amount of water may leak out during the bleeding process. It may also be necessary to push through the bleed valve stem, which is just below the screw, this is true for most modern CN models..
Removing air from the circulation pump
Air locks in a spiral type heat exchanger are rare, but very dangerous. The evidence of an airlock inside the boiler is water hammer: crackling and knocking due to intense steam generation. Burnout of the walls of the heat exchanger in this mode of operation is guaranteed, especially in solid fuel boilers. To release the air, you will have to close the shut-off valves, undo the threaded connections and fill the boiler with water manually.
In addition to the Mayevsky taps mentioned above, other types of sanitary fittings are also used. In the broadest sense, the role of a drain can be performed by any crane in general, but modern means are more convenient.
The check valve can be used as a manual air vent
For example, using a simple non-return valve, you can release air by simply pressing the stem with your finger. In this case, even the slightest flow of water is easy to detect and immediately release the stem, even if the bleed valve is located in a very inconvenient place. Instead of conventional check valves, there are specialized ones with a similar device, but a more convenient mechanism for pressing the stem under excess pressure..
Automatic air vents
Finally, there are automatic air vents (air vents), with which most modern boilers are equipped with all the necessary built-in piping. The same devices can be purchased separately, they are installed at the highest point of the system and, working fully automatically, eliminate air in 99% of cases.