本发明涉及一种具有至少一个气缸（3），其特征在于，所述气缸（3）中的活塞的泵两个独立的浮动活塞的活塞泵（1，2）被布置。 此外，本发明涉及一种还原剂用于注入还原剂成用于选择性催化还原的内燃机的废气流，其中，所述配量系统是/连接可连接到还原剂罐，取出的还原剂的并输送通过计量泵的装置和至少一个喷嘴到内燃发动机的废气流计量系统 被引入，其中计量泵是这样的活塞泵。

The invention relates to a piston pump having at least one cylinder (3), wherein in the cylinder (3) of the piston pump two independently floating piston (1, 2) are arranged. Further, the invention relates to a reductant dosing system for injecting a reducing agent into the exhaust stream of an internal combustion engine for selective catalytic reduction, wherein the dosing system is / connected connectable to a reduction agent tank, taken out of the reducing agent and conveyed by means of a dosing pump and at least one nozzle into the exhaust stream of the internal combustion engine is introduced, and it is a piston pump with the dosing pump.