Certain pumps require a complete separation of the hydraulic oil from the medium to be pumped. This is important for pumps used in some applications in food industry or for pumps operating at temperatures which are considerably higher than the maximal temperature of the hydraulic oil.
In this case the HP - barrel is linked to the hydraulic cylinder with a stand off. The stand off absolutely separates the hydraulic oil from the HP barrel. The design of the barrel depends on the special operation conditions.
The approximating switches are mounted to the stand off instead to the wall of the hydraulic cylinder. This allows better maintenance and also to control the stroke length in a certain range.
The pumps can have a constant or a variable flow rate.