The more modern version of the open-centred system, as shown above in diagram 9.28, is fitted
to such aircraft as the Cessna Citation. In this system, the reservoir draws fluid by a low-pressure
engine-driven pump and passes through a system bypass valve (off loading valve).
When a pilot makes a selection, the bypass valve closes, and the full flow is diverted to the
appropriate service. However, as seen from the diagram, the services are in parallel with each
other. This allows more than one service to be operated simultaneously.
Should the system bypass valve fail to open, the system does not generate any hydraulic
pressure. If the valve fails closed, the system relief valve, an FFRV, protects the system but
maintains a higher pressure. A filter is fitted down stream of the EDP, as this component is the
most likely source of debris due to wear. A discussion of filters occurs later in these notes.