What is Thermal Expansion and how do we account for it?

Thermal expansion occurs when the oil in the distribution piping is exposed to heat from space heaters or simply from the increased temperature at ceiling level. It causes an expansion in the system that can cause seals to leak, hoses to rupture and, in some cases, pump casings to crack. A common symptom is an excessively pressurized system at the first usage of the day. (A 1 degree F increase in temperature in a 25 ft hose reel can increase pressure by 40 psi).

Thermal relief kits are sized for the pump output pressure. They relieve small amounts of fluid back to the tank to prevent damage.