Wiekenberg no. 14-17 and Kochstrasse 19 with a total area of 12,000 square metres were acquired. On 1 January 1912 Gustav Mankenberg accepted his eldest son and employee for several years, Ewald Mankenberg, as a partner in the company. In his capacity as steam expert, he strengthened the company's consulting competence. On 1 January 1917 the second son, Hellmuth Mankenberg, who had worked as a technical merchant until the First World War after thorough practical and theoretical training in Germany and abroad, joined the company as a partner. He had retired from front-line service due to a serious injury. On 1 April 1919 Mankenberg transferred the company to his two sons Ewald and Hellmuth. He lived on the factory property until the complete bombing and destruction of his villa in August 1944 and died on 2 February 1945 in the German town of Greifswald at the age of 87. In 1929 the economic crisis began: Inflation and deflation posed new challenges to the company. During World War II the factory in Szczecin continued to fabricate steam valves until the eviction notice was received on March 23, 1945. The company had to be closed immediately. The company management was only allowed to take the finished products with them, all machine tools were not allowed to be loaded. The way led the company management and numerous employees to the Hanseatic city of Lübeck, where rooms were rented from the stamping and enamelling works. In the summer of 1945 the company was given permission to resume production in Lübeck. After initial provisional arrangements with company premises at five different locations, the company acquired the site at Brolingstrasse 51 in 1955 and built its own administration building on the factory premises. Dieter Mankenberg, one grandson of Gustav Mankenberg who was to take over the business later, was killed during WW II in Hungary in January 1945. Therefore, Dr.-Ing. Günther Weidner, son-in-law of Hellmuth Mankenberg, joined the company in 1954. In 1957 the limited company Gustav Mankenberg Armaturenfabrik GmbH was founded in addition to the existing general partnership (German OHG). Dr.-Ing. Günther Weidner received power of attorney. All employees were taken over by the GmbH. In 1967 the Lubeck-based graduate engineer Hermann Thomsen became head of the technical office. At the beginning of the 1970s, he also became a partner and sole responsible managing director of the company. In 1992 the company moved to Spenglerstrasse