In power stations and heat and power stations, there is often a necessity to reduce the pressure of superheated steam and to cool it to the temperature similar to saturation temperature. One element of reducing and cooling stations is steam pressure reduction valves.

In the presented solution, there was a necessity to reduce steam with pressure of 94 bar and temperature of 540°C to the pressure of 15 bar at the flow regulation of 80 t/h.

A valve having a welded structure, made with the body (1) made of a forged bar of 10CrMo9 10 (1.7380) material, was used. So as to compensate for the increase of steam volume during decompression, there is a need to increase the diameter of the pipeline at the outlet of the valve. Therefore, the valve body ends were designed as DN125 PN250 at the inlet and DN200 PN100 at the outlet of the valve. The axes of the inlet and outlet pipeline are not the same, which makes the valve body a “Z” type passage one (the name coming from the shape of the body).

Due to a high flow diameter of the seat (6) and pressure reduction of 79 bar, it is necessary to use a structure with a pressure-relieved plug (4). Relieving with the use of the pilot control plug (5) was applied. The pilot control relieves the main plug, at the same time regulating with high accuracy the minimum flows at the beginning of the opening. After the pilot control’s stroke, further regulation is realized on the regulatory cage (7) and cage of the main plug (4). In order to eliminate noise and to stage decompression of the medium at the outlet of the valve, two additional stages of choking in the form of multi-opening choking plates were used.

The bonnet of the valve was sealed to the body with a conical graphite ring (29). Thanks to that solution, the effect of caulking of the connection under the influence of pressure inside the valve was achieved.

The valve has a seat and a plug with V class of closing tightness – thanks to which it may also be used as a valve for the full cut-off of the flow.

It was manufactured for USS Košice in Slovakia – installed in the year 2009.