Hi what you have is termed hydraulic lock. My yacht has steering driven by hydraulics from the pilothouse steering and autopilot but mechanically from the cockpit
. So it is a bit more complicated than yours but I will describe the components relevant to your system.
I have three bypass valves for various scenarios and easy of use.
1) I have one directly ontop of the actuator ram for emergencies (ie if my electric
solenoid activated bypass jamms closed). I have never had to use this one.
2) I have a 12v solenoid activated bypass that actually closes the bypass when power is provided to it, thereby enabling hydraulic steering
. This can be activated by the autopilot (Raymarine SPX30) or a switch in the pilothouse when steering inside. It uses about 10 watts of electrical
3) I have another mechanical bypass valve located next to the solenoid one but it is operated by a telelever type cable which can be activated from the cockpit
This means that if I lose electrical
power (or just wish to save it) or the solenoid fails I have an easily accessible way of switching between hydraulic and mechanical steering.
Hope this helps