For compressed natural gas (CNG) vehicles, the first diaphragm of the low pressure regulator that supplies fuel does not have sufficient strength, and therefore, it may be damaged from repeated use, in which case the fuel density may become greater, causing erratic engine revs or starting malfunction. If this problem is left unattended, a backfire may occur, and in the worst case, the second diaphragm might be damaged, which could lead to a fuel leak.