To provide the necessary pressure in the heating system and to remove warmth carrier if there is too much pressure, right after the boiler, on the supply pipe, the so-called «safety group» is installed (see Figure 31), which consists of a pressure safety valve, a manometer, and an air purger. Sometimes these elements are supplied on the supply pipeline separately and it is necessary for the safety valve to be higher than the boiler, but more often, instead of several devices, only one is installed and it is simply a box in which the manometer, air purger and safety valve are sequentially installed. The safety valve consists of a valve stem which is pressed against a closing spring. The spring tension is determined by the manufacturer by adjusting the valve to a certain pressure; during installation, the valve can be adjusted manually according to what the manometer shows. As soon as the heating system has a failure and the pressure in the thermal circuit rises above normal, the valve spring can no longer hold the warmth carrier, the spring will contract and the valve will open — the pressure decreases and the extra warmth carrier will empty through the side outlet of valve. In order not to get burned when the valve suddenly opens, a drain pipe is screwed to the side outlet and directs the hot water to the sewer system. To monitor visually the cleanliness of the pipe (it can become clogged with sludge), discharge is carried through a funnel.