Selecting a feed water pump for a boiler is a crucial step, as it directly influences the safety and efficiency of the system. To make an optimal choice, several essential parameters must be considered, including pressure, flow rate, and hydraulic characteristics.
Safety Valve Pressure
The pressure at which the boiler’s safety valves are set is a fundamental element in the pump selection. To ensure safe operation, the pump must be capable of supplying water to the boiler even when the safety valves are activated. This means the pump must overcome the maximum pressure defined by these valves to allow for efficient filling under critical conditions.
Guidelines for Sizing the Flow Rate
To ensure a constant and sufficient water supply, even when the boiler is operating at full capacity, these practical rules are generally followed:
- With a modulating level valve: The pump’s flow rate should be equivalent to 1.25 times the boiler’s capacity.
- Without a modulating level valve (on/off control): The pump’s flow rate should be equal to 2 times the boiler’s capacity.
These safety margins help maintain an adequate water level in the boiler, even in the event of demand fluctuations or extreme operating conditions.
Calculation of the Manometric Head (Pump Head)
Selecting a pump is not limited to considering pressure and flow rate. It is also essential to calculate the required manometric head by taking into account several factors:
- Pressure losses in the feed and return pipelines.
- Elevation differences between the water level in the feed tank and the boiler’s inlet point.
A thorough analysis of these parameters ensures sufficient pressure to effectively supply the boiler.
NPSH: A Critical Parameter
Since boiler feed water is often at a high temperature, close to its saturation point, the available NPSH (Net Positive Suction Head) of the system must be carefully evaluated. NPSH ensures that the pump operates without cavitation—a phenomenon that can severely damage its components and reduce its lifespan. Special attention to this parameter is essential to guarantee the pump’s reliability and durability.