The monoblock design facilitates excellent circulation performance, yet requires little space. The motor can be replaced without having to completely disassemble the pump or without having to dismantle the mechanical seal. The maintenance-free bellow-type mechanical seal is highly resistant to wear and tear and not reliant on the direction of rotation. The seal is also lubricated by the medium via a circulation line, which makes it highly durable. The pump shafts of stainless steel 1.4571 is protected by a shaft protection sleeve also made of stainless steel 1.4571. This prevents wear and tear of the pump shaft.