Selection of parallel pumps
Thread Content
For a water pump with a flow rate of Q=1500 m3/h at normal temperature, calculated according to HG 20570, the head H is 51 m; therefore, a motor with a power of 280 KW should be selected. Now, the client requires two units connected in parallel; what size pump and motor should be selected? Originally, Q was calculated to be 750 m3/h and H to be 51 m (the pressure drop in the parallel portion of the pump changes very little); therefore, a motor with a power rating of 160 KW was selected. However, some people say that the curve shifts when pumps are connected in parallel; how should one make a choice?
Such change data cannot be found theoretically. Since the inlet and outlet piping becomes more complex when pumps are connected in parallel, this has a slight impact on the head; it is recommended to increase the head of the pumps connected in parallel by 1-2 meters. https://bbs.hcbbs.com/thread-1625897-1-1.html
1-2 meters of magnification might be a bit small. It’s a relatively old document, titled \"Process Design Data for Refining Equipment: Selection of Pumps and Motors.\" The required length was originally 240 mm; after parallel connection, it became 252 mm. The value he used was obtained by drawing a graph based on the pump’s performance curve.
1-2 meters of magnification might be a bit small. It’s a relatively old document, titled \"Process Design Data for Refining Equipment: Selection of Pumps and Motors.\" The required length was originally 240 mm; after parallel connection, it became 252 mm. The value he used was obtained by drawing a graph based on the pump’s performance curve.
If a smaller head coefficient was used in the original calculation for the pump, it can be increased slightly. However, if the pump’s head is significantly high, it will lead to increased operating costs.
I’m using an Excel sheet; most of the other fields can be calculated automatically, but I get stuck at this step. I don’t know; if these data are provided to the pump manufacturers, whether they can come up with a cost-effective solution. There are dozens of pump sets in the project; fortunately, most of them are backup pumps, so there is no need to consider parallel operation.
“However, some people say that the curve shifts after the pumps are connected in parallel. I don’t agree with this claim; there is no theoretical basis for it.
After the data sheet was submitted for procurement, the supplier returned the information; the power rating increased by one level, while the flow rate and head remained unchanged. I don’t know the exact reason. I would like to ask: 1. After increasing the power rating, can the head actually increase in practical operation, thereby compensating for the uncertain variations caused by parallel pumps? This is a concern for the designer. 2. If it is not a variable-frequency pump, at the same flow rate and head, will the output electrical power increase as the rated power increases? In other words, by choosing a motor with one size higher in power, apart from the higher costs associated with procurement and maintenance, will electricity consumption increase as well? This is a concern for the operator.
Regarding motor efficiency, the design institute does not have accurate data; generally speaking, the greater the motor power, the higher the efficiency. The manufacturer increased the specification, probably considering motor efficiency. 1. After the power level is increased, the actual head does not increase; the head is related to the impeller diameter, impeller angle, and rotational speed. 2. Power consumption will not increase.