Gas regulators have very small and intricate internal parts. If moisture enters the regulator, it starts to corrode these parts. For example, a needle valve has a tip that is actually about the size of a needle; if corrosion sets in, the tip can become rusted and fall off. Additionally, internal springs are made of steel, which can rust and break. Third, moisture can be dissolved in the gas itself. The United States Department of Transportation points out that water can enter a regulator through an exposed vent hole. (see reference 1, page II-8)
Gas regulators are designed to function when the pressure is within a certain range. If the pressure becomes too great, a relief valve is supposed to vent excess gas to open air. (see reference 1, page II-12, paragraphs 1 and 2) If the relief valve is frozen shut, excess gas will blow out gaskets and seals, leading to unregulated gas pouring out into the air.
The expert investigation and testing group Intertek gives an example of how improper valve closure caused a building explosion. (see reference 2) During their investigation of the explosion, they discovered the regulators had gone into lock-up when the wrong set of shut-off gas valves had been closed. (see reference 2) This had happened when exterminators, planning to fumigate the building by tenting, closed off the meter valves of apartment units, downstream in flow from the regulators, rather than the main valve, upstream in flow.The back pressure caused the regulators to lock up, blowing out their diaphragms. When the diaphragms blew out, natural gas leaked unabated into the tented building. Sparks from fans where suspected as the ignition source. (reference 2)
Lack of maintenance can be another cause of gas regulator failure. Because a regulator is a mechanical device, its parts can wear out. Needle valves and valve seats become dull, and rubber diaphragms become brittle and crack and spring lose their tension. Scott Specialty Gases notes that all gas regulators have to be inspected and rebuilt on a periodic basis. (see reference 3, points 5 and 6) The manufacturer specifies the maintenance interval. Failure by lack of maintenance is easily preventable if a regular inspection schedule is followed.