Radiator Pressure Caps of various sizes like Micro, Mini, Small and Medium of various pressures rating as per customer requirements. Under the top of the cap is a spring disc diaphragm (and upper sealing gasket on closed system caps) that seals against the top of the radiator filler neck and provides friction to keep the cap from working loose. The big spring is what maintains pressure on the coolant. The spring holds the pressure valve and lower sealing gasket against the base of the radiator filler neck to raise the coolant's boiling temperature and to keep it from escaping. When the pressure rating of the spring is exceeded, the pressure valve opens venting coolant into the overflow reservoir.

Radiator Pressure Caps of various sizes like Micro, Mini, Small and Medium of various pressures rating as per customer requirements. Under the top of the cap is a spring disc diaphragm (and upper sealing gasket on closed system caps) that seals against the top of the radiator filler neck and provides friction to keep the cap from working loose. The big spring is what maintains pressure on the coolant. The spring holds the pressure valve and lower sealing gasket against the base of the radiator filler neck to raise the coolant's boiling temperature and to keep it from escaping. When the pressure rating of the spring is exceeded, the pressure valve opens venting coolant into the overflow reservoir.