The direct acting pressure relief valves are used mainly in the hydraulic sections of the mining cover as the peripheral pressure limit valves in the receiver. The direct task of the pressure limit valves is to secure the hydraulic system against excessive pressure increase in the forced hydraulics units for protection. Indirectly, the pressure relief valves secure the most responsible units and elements of the mechanised mining cover section against damage or failure resulting from pressure increase. They guarantee the supporting value of the work section of the mechanised mining cover by means of maintenance of the working pressure in the sub-piston chambers of stands, roof-bar servo-motor chambers, front guard servo-motors, pulled and deflecting roof-bars and certain mechanised cover section correction servo-motors within the limits of values not exceeding the assumed ones and equal to the pressure for which the given valve was set..

Pressure Relief Valve Category IB
Pressure Relief Valve Category II
Pressure Relief Valve Category III
Pressure Relief Valve Category IV