There are a lot of ways that errors can creep into the compression test process. Right away I want to spend more money on better tools (can never go wrong with more tools). There is the unswept volume issue. The CTA 2800 kit seems to minimize that by having the Schrader near the tip of the adapter. Still, there is a little. You could put a Schrader into the tip of the HF injector and that would improve it. More precise skills and tools that I don't have. The pressure gauge is also suspect.
So, I decided to see what I could come up with using stuff I have laying around the shop. I am used a 16 penny nail and a piece of brass tube coupling to stuff into the HF adapter. The nail was a close fit and just had to be cut and slotted. The brass part was upgraded to a bulkier aluminum spacer which had to be drilled out slightly. It's a loose fit.
Using a syringe, I measured the volume of the hole in the HF adapter (with the HF pressure gauge adapter screwed in) at 1.7 cc and the nail/sleeve insert at 1.2 cc, so I reduced the unswept volume from 1.7 cc to approximately 0.5 cc. The plated pressure gage adapter has a Schrader valve.
I haven't yet found a way to check the HF gauge at 500 psi, but it does pass a test to about 130 psi with my Craftsman compressor gauge.
It will be interesting to see if this modification works at all and how the results compare with and without the inserts. That might not happen until the rainy cold weather improves since I can't work inside.
Comments?
The whole kit (Brass spacer not used):
The modified spacer and nail (16 penny):
The nail in the injector:
Nail near tip of adapter: