Pressure drop across the narrowing device: why do it in a heating system - Setafi

The pressure drop across the narrowing device is the difference between the indicator before and after a special element - the elevator. This is a metal part with a nozzle and a mixing chamber, which ensures normal pressure and speed of water movement through all heating pipes. More details about its structure and purpose are described in this material.

Why you need a pressure drop

It is intuitively clear that the pressure in the entire heating system must be the same so that the load is distributed evenly. Indeed, inside all the pipes and radiators of the house, the indicator is approximately the same (atm. – atmosphere):

• in a house with one floor 0.1-0.15 MPa (i.e. 1-1.5 atm.);
• in a building with 2-3 floors 0.2-0.4 MPa (i.e. 2-4 atm.);
• in an ordinary apartment building within 10 floors 0.5-0.7 MPa (i.e. 5-7 atm.);
• in high-rise apartment buildings, the pressure can reach up to 10 MPa, i.e. 10 atm.

The pressure is constantly monitored by pressure gauges and sensors that are installed in several places in the heating system:

• near filters, valves, traffic regulators;
• before and after circulation pumps;
• in the direction of travel of the main central heating system;
• before and after the heating boiler (if the heating system is individual).

It is clear why create pressure in the heating system - it is necessary to pump water to the house and further to the upper floors. But this also requires a drop in the range of 0.20-0.25 MPa, which corresponds to 2-2.5 atm. Due to this difference, a constant movement of water in the circuit is ensured, and at a strictly defined speed. Due to this, the differential pressure performs several functions:

• ensuring normal temperature in each apartment, in each room;
• uniform flow of water;
• prevention of strong drops and accidents;

Differential pressure and restrictor

The pressure drop is provided by installing such an important element as an elevator in several places of the heating system. This is a metal part that mixes hot and chilled water (the first one enters through a straight pipe, the second one - through the reverse, i.e. return pipe).

As you can see in the figure, the elevator consists of several elements. The principle of its operation is this. The hot water flow moves from the boiler house or CHP and enters the nozzle (indicated in red). This is the narrowing device, which increases the water pressure, creating the necessary difference of 2-2.5 atm.

When passing through the nozzle, the pressure increases abruptly, water enters the mixing chamber, where the cooled liquid also enters through the return line. Thanks to this, the coolant is cooled to the desired temperature and then goes through the neck into the diffuser chamber, and then into the apartment. Thus, the elevator performs 3 important tasks - it provides:

• desired temperature;
• the right pressure;
• a certain speed of water movement.

Elevators are installed immediately before the water enters the consumer.

From this review it is clear why pressure is needed in the heating system, as well as the purpose of the narrowing device. It is it that creates the necessary difference, due to which a certain speed of water flow is ensured. As a result, each apartment receives the same amount of heat, and approximately the same pressure is maintained inside the circuit.