Have a little question on SSIV control which some of you may know about it.
I'm trying to do an architecture for SSIV Control but slightly confused on the way it is controlled. In our scenario we have and SSIV on a seabed and umbilical with hydraulic supply from hydraulic power unit (HPU) running from topsides. SSIV is a failsafe spring return type of valve and the question is on which end we place a solenoid valve to release hydraulic pressure?
My thoughts it is better to release pressure topsides (activate topsides valve from ESD) and then fluid comes back to HPU.
Another scenario is when solenoid is on the SSIV on the seabed and fluid released to the sea or to the return line.
Could anyone please advice how it actually should be? I think it should e scenario 1, but in this case how do we flush the hydraulic line to clean the fluid?