By decrease of pressure in measuring and regulating stations, the gas is getting colder because of the Joule-Thompson effect. High differences in temperature can cause problems in the regulation path. Therefore the gas is being preheated in separate heat swappers. For that use we have a boiler with warm water heat system. The pressure in warm water heating system is lower then the gas pressure. Damage on heat swapper, can lead to the rise of the pressure in the warm water heat system. To prevent damage on the system it is recommended to install safty lock valve SSV-W/MRT on the input and the output side. Safety lock valve SSV-W/MRT is made compatibly with norm DIN 3381 work letter DVGW-G499, and its advantages are: narrow tolerance of come alive pressure, simple function test, simple construction, low pressure loss, DIN - DVGW approval.