Using a Dwyer Questions

[csababubbles]

I have a rmb with stainless steel valve model. Can someone please tell me how to use this to measure my skimmer pumps? The airline to the pump is a 3/8 inch inner diameter tube. The dwyer has two holes, one on top and one on bottom. If I attach the tube that goes to the skimmer pump tothe top hole, it fits in tightly but does fit, and it sucks in air which causes the little ball to rise. If I turn the big knob on the bottom all the way it stops the ball from rising. If I open it a little it rises again. Is this how I use it to measure my pump? Or do I stick the pump tube into the bottom hole? It won't fit into that one, it looks like I have to use a ro/di tubing as an adapter if I wanted to use the bottom hole.

So how do I use it? Something a little curious, I got two pumps that are supposed to each pull over 40 scfh and if I put the tube into the upper hole it only reads 20 scfh for each of them. Is it because I am using the meter wrong or the pumps are messed up?