What flow rate and head should the selected water pump have?

When selecting a water pump, we need to make a decision based on the requirements of the end devices (flow rate and pressure) as well as the actual conditions of the system (such as pipe length, pipe diameter, and resistance losses in the pipes). Based on the information you provided, the flow rate requirement is 5 cubic meters per hour, and the water pressure requirement is 2 kilogram-force per square centimeter (equivalent to approximately 19.6 meters of water column). ### To calculate the head, first, the required water pressure is given as 2 kilogram-force per square centimeter. Converting this to a head value gives: $2\ \text{kilogram-force per square centimeter} \times 10 = 19.6\ \text{meters}$ This is the net head required at the outlet. However, when actually selecting a water pump, it is also necessary to take into account the resistance losses in the piping and certain safety factors. Assuming the pipeline resistance loss is approximately 10%, then: $Head = 19.6 meters + 10\% \times 19.6 meters = 21.56 meters$ To ensure a sufficient safety margin, it is advisable to choose a water pump with a slightly higher head, such as around 25 meters. ### Calculating flow rate: Regarding flow rate, you have specified a requirement of 5 cubic meters per hour; when selecting a water pump, choose one with a flow rate corresponding to this value. It is also advisable to include a margin of safety, for example by choosing a water pump with a flow rate of 6 cubic meters per hour, to ensure that the flow rate requirement is met under all conditions. ### Regarding the water inlet of the pump, whether it can be connected directly to the tap water supply depends on the specific type of pump and the operating conditions. Some pump designs can draw water directly from the tap water supply, but it is necessary to ensure that the pressure and flow rate of the tap water supply meet the requirements for the operation of the pump. If the flow rate in the pipeline is lower than the minimum operating flow rate of the pump, it may cause the pump to run idle or experience insufficient suction, affecting its proper operation and lifespan. It is recommended to consult the pump supplier or a professional to understand the specific requirements of the pump as well as the actual conditions of the water supply system before deciding whether to make a direct connection. In summary, you may need a pump with a head of at least 25 meters and a flow rate of 6 cubic meters per hour. When connecting directly to the water supply pipe, it is necessary to carefully consider whether the flow rate and pressure of the water meet the requirements of the water pump. .

May I ask, if there are 20 nozzles and the pressure is 1 kilogram when 10 of them are open, how low will the pressure drop when all 20 nozzles are open? If I want to open 20 nozzles, the pressure still needs to be 1 kilogram – how do I calculate this?

When all 20 nozzles are open, in order to maintain a pressure of 1 kilogram per nozzle, the flow rate of the water pump must be twice that when 10 nozzles are in use. As the flow demand increases, the pressure loss in the system also rises, so the head of the water pump needs to be adjusted accordingly. If the total flow rate of 10 nozzles is 5 cubic meters per hour at a pressure of 1 kilogram, then the total flow rate of 20 nozzles should be 10 cubic meters per hour to maintain the same pressure. The selection of a water pump should be based on the ability to provide a flow rate of at least 10 cubic meters per hour, as well as sufficient head to overcome the pressure losses in the system. To calculate the head requirement of the water pump when all 20 nozzles are open, we also need to consider the pipeline characteristics, nozzle characteristics, and potential pressure losses. We can simplify this as: the head requirement when operating at full flow rate is equal to the head requirement when 10 nozzles are in use, plus the additional pressure loss caused by the increased flow rate. It can be calculated as follows: 1. Determine the flow rate per nozzle when all 10 nozzles are in operation (0.5 cubic meters per hour). 2. Use the relationship between flow rate and pressure loss (usually a multiple of the square ratio of flow rates) to calculate the pressure loss when all 20 nozzles are open. 3. Adjust the head of the water pump to ensure that the system pressure remains at least 1 kilogram when operating at full flow. Generally, an increase in flow rate leads to an increase in pressure loss that is proportional to the square of the flow rate. However, if there are no specific data on pipeline losses, you need to obtain more accurate head requirements through actual measurements or by consulting an engineer. It is highly recommended to consult professionals when designing such systems to ensure their safe and efficient operation. .