My first try at replying to a posting so sorry if it all goes wrong.
I thought I could add my solution.
My Honwave has Halkey Roberts valves and have made up a gauge to test pressures, I have 2 similar gauges so check them against each other every now and then.
I use these fittings and bought the grey one on ebay, it has a small screw inside that you adjust to lift the valve off its seat,(I think it came from Force4).
The second black one came with the boat and has a small moulding inside that also lifts the valve but is not adjustable.
I also have a grey one fitted to my pump so it is not pumping against the valve spring.
I hope the photos are clear enough to see details