On 6th and 7th August 2019, we successfully interrupted the flow of gas in the high-pressure pipeline DN 500, whose operator, and, thus, the end customer of our services, was GasNet, s.r.o. The operation took place near the village of Zámrsk at Vysoké Mýto. We used our newly developed device STOPL-S-F1 DN 500 at a reduced operating pressure of 5 bar. All the works were carried out successfully, and the implementation company I. SPZ, s.r.o. could, therefore, safely remove the required drainer. The use of our STOPL-S-F1 device for closing high-pressure pipelines under reduced pressure offers a safe, inexpensive and straightforward solution.