a pump system suitable for pumping a hot medium , such as hot mixtures of liquid and solid substances , includes at least one displacement pump , such as a membrane pump , at least one bidirectional flow pipe , and a second pipe connected to the pump chamber of the displacement pump . the bidirectional flow pipe is connected at a first end to a first and a second one - way valve . a supply pipe for drawing an amount of medium from the supply pipe is connected to the bidirectional flow pipe via the first one - way valve and a discharge pipe for discharging an identical amount of medium from the bidirectional flow pipe is connected to the bidirectional flow pipe via the second one - way valve . the second pipe is provided in a horizontal plane . the displacement pump is associated with an expansion accommodating feature to allow the displacement pump to move when the bidirectional flow pipe or second pipe expand . a partition element is provided in the bidirectional flow pipe to restrict flow through the pipe .