- Causes and consequences of airing the system
- Air removal methods
- Air Vents
- Air separators
- Installation points of air vents
The occurrence of “air locks” in a distributed system of pipes and radiators of a water heating system is a natural and frequent phenomenon. And for heating to be effective, this air must be regularly removed from the system. In this material, we will consider effective methods for manual and automatic air removal..
Causes and consequences of airing the system
Dissolved air is always present in water. And if at the stage of water treatment harmful impurities in the form of suspended particles and salts can be removed using filters, then the dissolved air cannot be removed in this way.
The state of a dissolved gas in a liquid depends on two factors – temperature and pressure. And since they are different in the heating system in different areas, the gas in the liquid can collect in microbubbles, and vice versa – dissolve again. And in that, and in another state, air is “harmful” for the system. Oxygen dissolved in the liquid leads to metal corrosion, and microbubbles can “stick together” in the form of large bubbles and form air locks that impede the normal circulation of the coolant and the operation of the equipment.
Another natural reason for the appearance of air in a closed system is the diffusion of gas through the walls of pipes and equipment. To some extent, it is always present, but the lower the density of materials and the higher the temperature of the medium, the higher its speed. The most vulnerable in this regard are polymer pipes, therefore, for heating systems they are produced with a special coating or an inner metal layer that partially compensates for this factor..
The technical reasons for the appearance of air in a closed system include leaks in the connections of pipes and equipment..
Gas can be released as a result of chemical and electrochemical processes. In aluminum radiators, when direct contact of aluminum with water occurs, a reaction occurs, during which hydrogen is released. The consequence can be a sharp increase in pressure exceeding the permissible threshold for equipment with the subsequent breakthrough of pipes, fittings or heat exchangers..
There are also “organizational” reasons: incorrect (fast) filling of the system at the beginning of the season, preventive and scheduled maintenance work in the off-season, repair work during operation, etc..
Air removal methods
There are two fundamentally different types of devices for removing air from the system: air vents and separators:
- Air vents – remove naturally evolved air from the system (in the form of large bubbles).
- Separators – work with air dissolved in a liquid. As the name suggests, they separate liquid and gas. First, conditions are created for the formation of microbubbles, which are then “collected” into large bubbles, taken to a special chamber, and from there, using a special automatic valve (air vent), they are vented into the atmosphere.
Naturally, it is impossible to remove all the air from the system in one cycle, especially taking into account the penetration of new portions into the coolant. Therefore, the process must be systematic. But if the separators work in automatic mode, then the air vents can be automatic and manual.
The principle of operation of air vents is based on the use of a needle valve.
In a manual air vent, a classic Mayevsky tap, the shut-off valve moves in a hollow cylinder, which has an opening from the inside to the system, which is closed with a tapered needle. There is a bleed hole on the side of the cylinder. Both the head (or body) of the needle and the corresponding inner cavity of the cylinder are threaded.
In the closed (screwed) state, the valve is locked, when the valve head is unscrewed (with a screwdriver or key), the hole opens and air from the system enters the cylinder cavity and then outside. There are models with a more complex design, in which the valve is operated with a handle, and the locking element is made in the form of a plate.
The automatic air vent valve is actuated by a float. Therefore, unlike the Mayevsky crane, the working cavity of the valve cylinder (in which the float moves) must be in a vertical state. For heating circuits with lower wiring, the air vent is installed directly next to the boiler as part of a security group.
In the absence of excess air in the cavity, the float is at the top and closes the valve. As air accumulates (gas tends to compress), the pressure on the float will increase. When a certain pressure level is exceeded, the float will lower and the valve will open – the air will come out, the coolant will take its place, the float will rise, and the valve will automatically take its original position.
1. Air valve mechanism. 2. Float valve. 3. Float. 4. Connecting pipe
The operation of most separators is based on the fact that with a sharp decrease in the flow rate of the coolant, the air dissolved in it is released, forming bubbles. The separator body is made in the form of a flask, in which there are elements that slow down the flow. Each manufacturer can set its own “moderator” of a special shape:
- perforated wire-braided tubes;
- rolled mesh;
- mesh baskets;
- systems of rings of different diameters.
In addition to slowing down the flow and creating zones with different pressures, the surface of these elements serves as a kind of “catalyst” for the formation of large air bubbles – when in contact with it, the microbubbles stick to it and to each other.
Another type of separator first “accelerates” the flow by passing it into the flask through a narrow nozzle. But falling into the inner plane, the flow rate drops sharply, the pressure decreases, and the dissolved gas is released in the form of bubbles.
There are air separators that use centrifugal forces. When the coolant is supplied through specially oriented nozzles, it swirls in the flask, while the liquid flows to the walls, and the air is concentrated in the center and floats to the surface of the funnel in the form of bubbles.
Regardless of the type, the supply of the coolant outlet in the separators is carried out in the lower part of the housing, and the air outlet is in the upper part. The upper part is arranged according to the same principles as for automatic air vents.
1. Air valve. 2. Float. 3. Separator mesh. 4. Inlet branch pipe. 5. Outlet branch pipe. 6. Sludge collection chamber. 7. Outlet valve for cleaning the separator from sludge.
In addition to “clean” models, there are also combined ones. They combine air and sludge removal functions.
In heating systems using several pumps, a hydraulic arrow is installed between the boiler and the collector. The flows in it slow down, and its body is large enough to arrange an air separator in the upper branch (in the supply), and a sludge separator in the return. Therefore, some manufacturers integrate three functions into this device.
Installation points of air vents
In a city apartment connected to a central heating system, air vents are mounted directly on the heating batteries in the free top collector instead of a plug. The control of airing the battery can be carried out simply by observing the heating efficiency of the radiator, therefore the most common Mayevsky taps. But there are also special automatic radiator air vents with small chambers and a compact body. Also, corner models of automatic air vents can be installed on radiators, which are used on collectors.
It is best to install the air vent as part of a safety group at the highest point of the heating circuit and as close to the boiler as possible
Autonomous heating systems use a multi-stage air removal scheme. That is, a piece of equipment is added to Mayevsky’s cranes, which the inhabitant of a city apartment simply does not see:
- After the boiler, in front of the circulation pump, an air separator is mounted.
- Automatic air vents are installed at the top of each branch of the heating system and on the collectors.