Ok I been playing with this a good part of the day. I have some issues!!!
First there are 2 different manufacturers of these pumps!! And yes they are different. I installed my pump and got no flow at all. The check valves in the top were good and I got a good siphon through it but no pump action at all. I thought that maybe a shortcut I had taken was the problem. I had cut my screw down to about 1/2 inch and it was too long so I added a couple of washers under the head. It went together fine but I am pretty sure the head clearance against the top of the pump was inadequate for good operation.
So I took it apart again and cut the screw down some more. I was comparing the pumps and realized the the lever that rides on the cam on the one I was working with had a Lot more free movement before I felt any load from the big spring under the Diaphram. So I kept cutting down the screw and checking it. I got to the point that I have no washers at all under the head of the screw and I still have too much freeplay on the lever when the cap is on. I suspect that in the unloaded position the Screw head is hitting the top of the pump cap and that @ 1/8 inch of lost movement is preventing a good flex of the Diaphram. I am kind of guessing that this is the problem right now. Tomorrow morning I will grind off the head of the screw and leave just enough metal to hold things together and try it again. I am expecting a somewhat reduced flow due to the thickness of the material. This stuff measures at about 1.5 mm and the one that came out was 1.25mm.
The pics below are just to illustrate the differences between the 2 different manufacturers
The 2 different caps