Motorizied flow control

[YPetcho]

Hello
I came up with an idea to control the speed of a piston and use it with precision and i wanted to make sure its legal.
we bought 5 ports - 3 position valves so we could stop the piston at any position we want, but we had a problem, the piston is moving too fast for the drivers to control it well.
so i attached flow control tubes to the relief ports in the valve
http://www.andymark.com/product-p/am-2690.htm
its worked well but if we wanted to open the pistons fast we couldn't do so.
so i connected a hobby servo with a gear ratio to the screw on the flow control tubes so i can control the speed of piston with driving.
is this legal?

tnx in advance