Manufacurers of Sub Sea Hydraulic Actuators. I received enquiries for valves c/w hydraulic actuation on occasion and never seem to have much options.
The Dantorque's are beautiful compact actuators, but tend to be on the pricy side.  I don't know how the helical spline would hold-up for extended modulating service.  This would be a very expensive part to replace if you had too.
Best to talk to your local rep for more specific info.
However, as these are quarter turn actuators, I don't think they would work for Subtek.
I think the problem is that not many people supply sub-sea hydraulic actuators for linear applications, especially small needle valves.  Maybe if you opened up the floor to other valve types, you might see other options for the actuator as well.

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