§ 322. Standard of pressure. The minimum pressure of gas so furnished or supplied which shall be permitted in any service main in any such city shall be sufficient to balance a column of water one and one-half inches in height. The maximum pressure therein allowed shall be an amount sufficient to balance a column of water three and three-fourths inches in height, plus an allowance at the rate of one inch for variation of each one hundred feet of increase in altitude in the distributing system between the holder and the point of consumption, except that no maximum pressure shall be prescribed in service mains the pressure of gas from which is regulated by service governors, supplied and maintained without charge to consumers.