The two-level control system of release is used. This system reduces counter-pressure when opening and when closing the adjustable valve which is located in the main muffler, thus changing pressure of the fulfilled gases. The valve opens бесступенчато according to power setting, ensuring thus more silent functioning in the range of low frequencies of rotation of the engine and reducing counter-pressure in the range of higher frequencies.

The operating valve is located in the main muffler. When pressure of the fulfilled gases overcomes effort of a spring, the operating valve opens depending on the size of pressure of the fulfilled gases.

Work (see fig. 2.27)

Fig. 2.27. Scheme of work of a two-level control system of injection: 1 – the operating valve is closed; 2 – the operating valve is open; 3 – the fulfilled gases

The operating valve is closed (low turnover of operation of the engine).

As pressure in the main muffler is not big, the operating valve is closed. Therefore, the fulfilled gases do not pass through the roundabout channel, and noise of an exhaust is reduced by the main muffler.

The operating valve is open (average and high turnover of operation of the engine).

The valve opens with growth of frequency of rotation of the engine and counter-pressure in the muffler. It allows the bigger volume of the fulfilled gases to pass through the roundabout channel, thus counter-pressure significantly decreases.