the piston neck 28 between them when the reciprocating piston pump of the invention is put together first the cylinder 4 and 5 with their pistons 6 and 7 are installed in the housing 3 then through the bore 14 the hoop spring 11 with its free ends 36 36a and 37 essentially leading is moved and pressed toward the piston necks 27 28 as a result because of the protrusions 38 38a and 39 the resilient arms 33 33a and 34 are moved elastically apart so that the protrusions 38 and 39 slide over the piston necks 27 and 28 and can snap together behind the middles of these necks as a result the piston necks 27 and 28 are locked in detent fashion into the hoop spring ends 32 and 33 the hoop spring 11 is now pivoted into the alignment especially clearly shown in fig2 and 3 after that the shaft 8 can be thrust between the piston ends 23 and 24 with the stop ring 21 which is conically embodied for this purpose leading this opens the hoop spring 11 elastically wider upon further motion of the shaft 8 the outer ring 18 finally comes to be located between the piston ends 23 and 24 and the roller bearing 15 also plunges all the way into the bore 14 as can be seen from fig2 and 3 the stop disk 12 then takes its place adjoining the two continuations 40 and 41 in fig2 there is an equal length spacing shown between each of these extensions 40 and 41 and the stop disk 12 but this spacing is not preserved during operation of the.