What should each blowdown pipe be equipped with?

Each blowdown pipe should be equipped with two valves or one valve and a cock. This requirement is put in place to ensure proper control and isolation of the blowdown process, which is critical for the safe operation of the boiler.

The presence of two valves allows for a level of redundancy and safety. For instance, one valve can be used to isolate the system while maintenance or repairs are being performed, while the second valve can still allow for safe blowdown operations. If one valve fails, the second one provides a backup means of controlling the blowdown, which helps prevent potential hazards associated with excess pressure or temperature in the boiler system.

Having a valve and a cock also provides flexibility in operation. The cock can be used for minor adjustments or to drain small amounts of water without the need to open a larger valve, which can be more disruptive. This design increases operational efficiency and safety.

In contrast, some of the other choices would not meet the standardized requirements necessary for safe blowdown operations. For example, having just one valve does not allow for safe isolation during maintenance, and having three valves could complicate the system unnecessarily without added benefits. A pressure relief mechanism, while important in other contexts, is not a primary requirement for blowdown pipe configurations