The supply reservoir is protected from being over-pressurized and bursting by a safety valve (Fig.17). This valve is pre-set (usually at 150 psi [1,034 kPa]) and will blow off excess pressure. Once pressure is lowered, the safety valve will re-seal until an over-pressurized condition exists again. If a safety valve blows off excess pressure, this indicates a problem with the governor. The problem should be dealt with immediately by a qualified person.