Stop in for a cup of coffee

Ok guys. I made a compression tester today. Crimped together a 10,000 psi hydraulic hose. Put a norgen air gauge. And ground down a spark plug and welded a nipple on it. Question though. Do I need a check valve on this thing?View attachment 1715534222 View attachment 1715534223 I never did a compression test. But common sense is telling me yes.
Yes, I think so. Many of them use something similar to a tire schrader valve.....Mine do....