Zeroing BII Vacuum Gauges

[RC Maple]

I was getting my Shurflo pump cleaned and ready to put away when I found some plumbing improvements I could make to the manifold at the strainer. I thought I would check this out and get it as good as I could before putting it away. I noticed my vacuum gauge was not at zero but was around 5 in Hg while just sitting there. After a YouTube search, I could not find a way to zero this style of gauge. I took the cap with the lens off and removed the pointer and reinserted it so it read zero. Although I am sure I made improvements, the BII gauge didn't think so. What was a 25 reading on the gauge was now an 18. Ok, that could be... if what I worked on wasn't really hurt my vacuum. After tinkering some more I noticed before running the system again, the gauge now reads 20 - at rest with the system off and valves open. I did the same gauge adjustment as before and now when running, I am getting 10 in Hg for the reading. I am wondering of my gauge zeroing is what is making my numbers drop. I have other gauges I can try tomorrow but still the question - can these be adjusted or are they just bad?

These are not liquid filled. There are two screws on the backside, but they only attach the face to the back.

[SeanD]

Sounds like a broken gauge. Put a new one in and buy some extras while you are at it. They break, so it's always good to have a replacement or three on hand.

[Bricklayer]

They are not adjustable. Once the get some liquid in them I find they are screwed. Even if they were adjustable I would trust them. I usually buy a box of 10 every couple years. They are pretty cheap on Amazon.

[RC Maple]

Sounds like good advice. I'm getting some new ones.