SiZ 1508
Full-lift safety valve with additional loading
Inlet: DN 25 to 350, PN 16 to 400
Outlet: DN 40 to 600, PN 10 to 160

Body is angle, with possibility of either flanges on both ports, or weld ends or combinated. Inlet port is of a nozzle type, outlet port is extended. There are welded lugs on the valve body for gripping the valve to the load-bearing structure and absorbing reaction forces. Plug, equipped with an additional flat for achieving of stronger lifting force, is pressed by the means of the spring and pressure air cylinder to the seat. There is a differential piston moving inside of pressure air cylinder to which the lifting and loading airs are supplied through the hoses from the control unit. The valve is set and adjusted by its producer to the opening pressure specified in the customer´s order. Such a setting is secured against an unallowable interference. Dimensions of connection flanges and weld ends are specified after the agreement between the producer and customer when the order is being technically cleared. Weld ends correspond to ČSN 13 1075 as standard, flanges correspond to ČSN EN 1092-1 (2/2003) [or 13 1060 (7/1985)] as standard.

The full-lift safety valve with additional loading is a valve designed for automatic protection of a pressure equipment (steam boilers, pressure pipelines, steam-conditioning stations, pressure vessels, turbine extraction etc.) against unpermitted pressure increase over allowable limit.
Certificate of the valve construction and guaranteed output of the safety valves type SiZ 1508 was issued by Český úřad bezpečnosti práce (The Czech Institute for Safety Work) in Prague, under ref. No. 1699/0.50/69 dated 24th of September 1969. From that moment the valves type SiZ 1508 were involved into the approved equipment of steam boilers according to ČSN 07 0620. The valve output guaranteed in accompanying documents is guaranteed only provided that the pressure loss in pipeline does not exceed 3% of opening pressure in inlet pipeline and 25% in outlet pipeline.
The safety valves SiZ 1508 are designed for water vapour, air, and non-aggressive gases and vapours. The highest temperature of securing medium is up to 575°C. The valves can operate continuously in dust environment with ambient temperature to 80°C. After consulting the producer, it is possible to pipe the valve in environment with ambient temperature below zero.
The valves are delivered and must be operated together with their accessories, i.e. control unit and aerating system. If these conditions are kept, the users can expect 100% certainty in the safety of the protected equipment, power energy savings and fast return of input costs. Single parts can be delivered only in case of the replacement for previously delivered equipment.

The valve function
The safety valve is controlled by the control unit. If the control unitis is for any reason put out of service, it may shortly operate just exceptionally or in case of emergency (pressure air supply failure, control unit breakdown etc.). Any longer operation or repeated service in such state may lead to a rapid reduction of the valve service life due to vibrations and leakage.
After reaching the opening pressure value, control unit let the air out of the space above the piston of pressure air cylinder. Air pressure plus securing medium pressure acting on the plug overcome spring force and safety valve then rapidly opens to full lift. When the pressure drops, then whole action runs reversed. Rapid opening and closing are just two main features of the valves.
In case of control air pressure supply failure, the force is induced by the securing medium pressure only. The valve opening runs incomparably more slowly than in the previously described state. As a result of it, the seat is excessively stressed and may get worn.

Catalogue sheets
Full-lift safety valve with additional loading typ SiZ 1508 CZ, GB, RUS, PL