I could not locate a globe valve locally that would fit the bill, so I ordered one online. Good ol' internet.
I question the whole setup as Watts discusses the 'pressure differential', then recommends a 'flow-control' style valve. Right now, the house that I am working on has the setup as shown in the diagram sans the valve on the cold-water feed side of the tempering valve.
History is that a new boiler was installed 4 years ago to replace the original 196? GM one. Two oil companies later and a complaint of no hot water, they replace the tempering valve with the Watts 70A and leave it set to its max of 160 deg. Another phone call to complain of no hot water and they suggest replacing the control valve in the shower. From what I understand, hot water has always been an issue, but no one is making a big deal.
This is where I come in. I replace the shower control valve as requested and still get no hot water – when I say no hot water, I mean that it is luke-warm at best. I check out the boiler and turn on the hot water to the sink on. I can’t touch the hot water pipe from the heat exchanger into the tempering valve but the ‘tempered’ hot water line is only luke warm. A little research brings up Watts installation instructions for the 70A valve and shows that it was not installed as per their instructions. Incidentally, when I turn the tempering valve down to 120 deg., the ‘tempered’ water turns cold. I have no question about the capacity of the boiler to provide hot water.
I’m going to install the globe valve in the AM and see what happens. If there is still an issue, I’ll keep digging.