Pressure Reducing Stations
Each station includes two identical pressure-regulating streams. The downstream systems are protected from overpressure conditions by:
- Pressure limiting devices :
Such as relief valves and monitor regulators where flow is maintained at a pressure slightly higher than normal and
- Automatic shut off valves :
which are activated in the unlikely event of failure of the primary and secondary overpressure protection systems. A sensing system identifies which stream has failed and activates the appropriate shut off valve, allowing the second stream to take over operation.
It is designed to permit isolation of main sections without disrupting gas flow to the remainder of the system. Manually operated valves are installed at key locations throughout the system, which allow damaged sections to be quickly and easily isolated.
Services to residential customers are fitted with a flow-limiting valve, which is automatically activated in the event of a major leak, almost completely cutting off the gas flow.
A manually operated shut off valve is installed in services to commercial and institutional premises.
Service (Primary) Regulators
A primary regulator is located on each service riser, which reduces the distribution pressure to an intermediate value. These service regulators feature token relief, overpressure shut off, and under pressure shut off.
If the set pressure increases beyond its normal value the relief valve will open and vent limited quantities of gas to atmosphere. Its capacity is approximately 1% of the regulator’s maximum flow.
Overpressure Shut Off
If the pressure downstream of the regulator increases beyond the relief’s capacity, the OPSO will quickly close and must be manually reset before gas supply to customers is restored.
Under pressure Shut Off
If the pressure downstream of the regulator falls due to a break in the outlet piping, for instance, the UPSO will quickly close, and must also be manually reset before normal flow is resumed.
Secondary regulators are installed just upstream of the customers’ meter to reduce the pressure to the value required for proper combustion in the appliance. Each secondary regulator incorporates an under pressure lock out feature which shuts off almost all the gas flow through the meter in the event of a leak in the house piping. Once the leak has been repaired, the downstream pressure will slowly build up to its normal level and the regulator is automatically reset.