[Rimrock]

One have the 'axial slide' valve, the most common in 1:1, and the 'rotate valve', most common in scale modelling. To find out how the valve are put together is not that big problem (google/youtube) but to make one at home that holds on to any pressure is the challenge. To have good success, miniature O-rings often are to be added in the correct locations in the valve, which most of the German miniature hydraulic producers have realized, but the chineese are struggling a bit more, as some extra O-rings will ad some cent's to the production cost it seams..or whatever. Maggom newest valveblocks and pumps seams to work okay, at a relative reasonable price..as your possible 'plan B'