We found that we would have the same issues after working with our Twinbot 'Betsy'. So we ordered 7/16" speargun tubing (from Amazon). That coupled with our lead screw we used for tensioning, we found that we could dial in as we needed. We used a donated pressure scale (much like a fish or deer scale) - it was from an old prison. The story is that it was used to check the pressure from the boiler unit. No matter, it DOES look like something from a prison.
In the photo, you can barely see the leadscrew - it is just to the lower-left of the speargun tubing.
