The check valves DCPP of the building sizes of the 20 and 25 are valves with preliminary hydraulic decompression.

To let the flux run free from P to T, the main stadium and the preliminary discharge are pressed together against the closing spring and let free the necessary section of the main stadium’s place.

In the inverse direction the sphere and the conical cursor are pressed from the closing spring and from the pressure acting on the T junction on the seats and the connection from T to P is closed without wire-drawings.

In case of a sufficiently high piloting pressure on the 3 junction it is earlier opened the preliminary discharge seat; that means the damped discharge of the fluid under pressure.

The further run of the cursor causes the opening of the main stadium and allows the free flux from T to P.

The pressure present on the P junction contrasts on the cursor the 3 junction’s leading pressure.

The hydraulic unblock is, then, possible just in absence of pressure on P junction.