Hmmm, I don't have data on the DHC-8 prop but most propeller governors essentially use two reservoirs of oil to change the blade angle. Conceptually it's something like this:
(Source: John Deakin - Pelican's Perch)
Pelican's Perch #16:<br>Those Marvelous Props
One reservoir provides the pressure to make the pitch more coarse while the other reservoir provides the pressure to make the pitch more fine.
Here's a schematic of the Superconstellation Hamilton Standard prop and governor that show's you more realistically how things are connected. Note the pressure oil and return oil used to control the pitch of the prop.
source:
http://www.superconstellation.org/Te...rop-schema.jpg