City Of Chicago Boiler Practice Exam

Open feedwater heaters rely on heated water to preheat the feedwater before it enters the boiler. If the water coming from the heater is too hot, its vapor pressure is high enough that, once the water is drawn into the feedwater pump, any pressure drop on the suction side can cause some of the water to flash into steam. That steam forms a pocket in the pump suction, filling it with vapor and preventing the pump from lifting liquid — a condition known as steambound. When the pump is steambound, it loses prime and can’t deliver the required feedwater to the boiler, risking boiler operation. Note that higher temperature does not reduce cavitation risk; it typically increases it because vapor pressure is higher. Also, while overheating protection may trip, the immediate pump-related effect of water being too hot is steambound, not an improvement in efficiency.