Mike you can get a low cost single probe controller at 24V and turn on and off a solenoid buy pass valve to keep your water with in a ½ inch of where you want it.
One probe in a one inch water column will do the trick.
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www.ssac.com]
What are you doing with a reflex gauge anyway, Stanley never used one.
There not even approved for over 300 PSI without a mica sheet and flat glass in them.
Rolly