Posted for "Randy" <randystuart@hotmail.com>:

 When opening the dump valve the pressure equalizes between the hi and lo
sides, this releases enough pressure to allow the sensor switches to come
alive. The hi and lo are still separated when the dump valve is closed. The
rising temp increases the pressures on both sides. I've seen the hi gauge read
as much as 2000 psi on a hot summer day.
 Randy Stuart
 LNC2

{Randy, I thought that the relief circuit inside the pump was designed in such a way to eliminate this possiblity.  If that isn't the case, then the addition of a couple pressure relief valves set to limit the circuit pressures could solve the problem.  They are readily available, McMaster Carr has them.  Go to http://www.mcmaster.com/nav/enter.asp?pagenum=447 and scroll down to the middle of the page, where the heading is "Steel Tamper-Resistant Adjustable Relief Valves"... Just another thought to add to the mix.   <Marv>   ]