From an ex marine engineer, albeit a long time ago, here's how it works.
On the bridge- Is the steering wheel directly connected to a small hydraulic pump. When rotated the delivery is piped to the steering flat located above the rudder.
In the steering flat- Is located the main hydraulic actuater connected to the rudder,the telemotor,an electrically driven, high variable delivery hydraulic pump which runs continuously.
Operation.- The main pump,although running does not deliver unless a change of direction is required. The telemotor receives any signal from the bridge ( By turning the steering wheel),and magnifies it,to operate the control lever on the main hydraulic pump which will deliver to the main actuating rams connected to the rudder. When the required change of direction is reached, the telemotor cancels the signal given to the main pump, and delivery ceases although the pump is still running. Hope this helps.