System in which the pressure at the hydraulic pump remains constant regardless of the flow rate and how high the load pressure is.
Strictly speaking, this is only really the case with:
- controls with throttles whereby constant pressure is maintained by allowing any oil flow not required to flow away via the pressure-limiting valve;
- variable pump with pressure controller which adjusts itsdelivery flow in line with consumption so the pressure in the system is kept constant.
Systems with hydraulic accumulators are also referred to as constant pressure systems, although the pressure here reduces as more used oil is removed (impressed pressure).
Constant pressure systems generally experience greater losses than systems where the pressure changes (Figure K 29), although they offer the advantage that loads connected in parallel can also be operated with one pump at the same time (e.g. parallel circuit). In the field of electro-hydraulic control technology, they are also essential for the high level of dynamic performance required.
Figure K 29: Constant pressure system