Complex sentence: From 1923 he served as the administrative director of the Mercaz HaRav yeshiva, and then after R.kharlap died in 1952 he became Rosh Yeshiva until his own death.
Split into simpler sentences: From 1923 he served as the administrative director of the Mercaz HaRav yeshiva. After R. Charlap died in 1952, he became Rosh Yeshiva until his own death.