Heating systems require precise control. They operate under high pressure, and this pressure can sometimes, for unforeseen reasons, increase to critical limits. Increasing the temperature of the heat carrier due to the failure of the heat exchanger control system causes water to boil. At the same time, steam is formed, which simply breaks the pipes. Expensive repair of heating, deterioration of furnish of a premise and burns of integuments - here the list of consequences which can arise at the negligent attitude to this question.

The pressure monitoring devices in the thermal communications are a pressure gauge and an automatic relief valve for the discharge of an overpressure. The first one helps to visually assess the performance of the system and prevent a failure in time. The second reacts quickly in critical situations, preventing destruction.

Pressure relief valve for water, air

Why the overpressure relief valve is needed

From the name of the device it is clear that the unwanted pressure in any system should be diverted, and this is the main task of the valve. But what is overpressure? The elements from which the thermal circuit is assembled, and this is mainly pipes, a boiler and pumps, are designed for a certain pressure inside them, the magnitude of which is determined by the wall thickness and the material of manufacture. When designing a specific heating system, all its components are taken with a margin of strength. Excessive pressure is considered to be greater than the nominal operating pressure of the system, but not exceeding the limits that can be destroyed by any heating element.

The overpressure relief valve is applicable not only in the heating system, but wherever there is pressure above atmospheric: hot water, steam and gas installations, air compressors.

The mechanism and operation of the valve mechanism

The arrangement of all types of protective valves is approximately the same. It includes a base and a movable part. The base is a hollow body with a threaded connection, by means of which it is fixed to the system. Inside the body there is a movable rod that can move in the longitudinal direction. This rod in a certain position holds the spring.

When the pressure in the system does not exceed the nominal, the stem is stationary and blocks the vent hole. If, for any reason, the pressure in the system begins to increase, then there comes a time when it exceeds the force of compression of the spring. The latter begins to feed and releases the rod. The rod moves to the side and opens the hole. Excess pressure is released and the mechanism returns to its original position. This process is accompanied by a sharp hiss and must attract attention to itself.

In what heating systems does the safety group apply

The most unstable and vulnerable in terms of pressure are steam heating systems. This is due to the fact that the adjustment of solid fuel combustion is very difficult to control, and in some boilers it is not envisaged. In a short time, the temperature in such thermal circuits can sharply increase, leading to the boiling of water. This is not terrible for open systems with the presence of an expansion tank, but at present they are rarely used. In closed circuits, valve installation is simply necessary.

In addition to raising the temperature as a reason for escaping from the control of the pressure level, water pumping devices can also fail in the system. Usually these are powerful pumps that are able to break pipes, or, working in idle, simply fail. In such cases, it is also desirable to use a reset device.

If the issue of cost savings is not worth it, then installing the overpressure relief valve for heating will always be correct. Only electric and gas boilers are less demanding in this regard, since they have a reliable system of temperature sensors for heat exchangers.

Types of safety and control valves

Professional heating systems have not one, but several pressure-relief sensors installed in the most sensitive places. A complete set of such systems contains:

  • Automatic overpressure relief valve. Devices come in different designs and are usually installed in each branch of the heating system. There are adjustable and unregulated mechanisms of this type. In adjustable, you can set any pressure threshold.
  • Reverse bleeding valve. It performs two functions: it directs the water flow to one side and relieves excess pressure.
  • Valve relief of excess water pressure ball. It is used to control the pressure in manual mode.
  • Straightening valve. It produces unnecessary air, creating congestion in heating mains and circuits. There are automatic types and manual adjustments. The latter is installed on each radiator.
  • The valve regulating the feed. Has inside the thermostat, changing the capacity of the valve until it overlaps. This type of mechanism is installed primarily at the entrance to the radiator to correct the temperature in it.

Rules for installing safety valves

That the valve reliably worked and in time reacted at the right moment, there are certain rules for its installation:

  • The device is cut into the system on the boiler outlet, so that the hot water pressure can be immediately reset.
  • Place the valve as far as possible at the top.
  • A discharge tube is connected to the valve outlet, which is sent to the sewage drain.
  • The diameter of the valve inlet should not be narrowed in the threaded connection, so as not to reduce the capacity of the mechanism.
  • It is strictly prohibited to install additional valves at the valve connection point.
  • The valve position should be in an accessible location for possible replacement and maintenance.
  • It is better to fasten the valve to the quick-release connection.

Selection of the valve according to the pressure rating in the system

Each individual heating system has its working pressure. It is determined by the parameters of the boiler. All safety valves must be designed to operate within this pressure range. Depending on the capacity of the system, valves of appropriate capacity are selected. For standard boiler types, the following are suitable:

  • Boilers gas wall mounted, operating at a system pressure of 1.5 to 2 bar - a 3 bar valve.
  • Gas floor boilers, rated for 1 to 1.5 bar, are a 3 bar valve.
  • Solid fuel boilers and furnaces with heat exchangers for pressures of up to 1 bar - a 1.5 bar valve.
  • Hot water supply systems with pressure up to 4 bar - overpressure relief valve for a 6 bar water heater.

For your reference: 1 bar equals 0.987 atmosphere.

Overpressure relief valve

Such a safety valve is mainly put on high-pressure compressors. They protect the pumping capacity from bursting and are often combined with the power switch of the piston mechanism. The principle of operation of these devices is similar to the previously considered dropping mechanisms. Only instead of liquid or steam, the pressure on the rod is simply air. Another feature of the compressor air valve is that after bleeding a part of the air the valve does not return to its original position. Its return and the inclusion of electricity occur only when the pressure falls below a certain level. That is, the valve operates at a certain pressure range.


The ideal option for the preservation of any heating system is the inclusion of a protective group in it, which includes an overpressure relief valve, a pressure gauge and a venting valve. Also in addition to them, it makes sense to supply thermal sensors that will shut off the heating equipment or include an additional cooling system when the coolant temperature exceeds a given level.