The most important parameters of submersible pumps
Specific pumps for pressing sewage and rainwater are described in many parameters resulting from the type of power supply, the type of medium that press, its temperature, chemical composition, solid fraction content and liquid density. However, there is a basic group of parameters from which we start choosing a pump and they are:
- Efficiency (flow) Q administered in liters or cubic meters per unit of time: [l/s], [l/min.] Or [M3/h]
- Lifting H served most often in meters [m], bars [bar] or atmosphere [ATM].
- Rated power P2 administered in kilowaty [KW]
- Rated voltage in volts [V]
- Rated electricity and in ampera [A]
- Power supply: single -phase 1 ~ 230 V, three -phase 3 ~ 400 V or sometimes 3 ~ 230 V
- Power frequency F administered in Herce [Hz]
- Engine speed n administered in rotation per minute [rpm] resulting from the number of engine poles: 2 ~ 2900, 4 ~ 1450 and less often 6 ~ 900 or 8 ~ 750 rpm
Other parameters such as engine efficiency, cosine φ or other resulting from the construction of the pump at this stage of consideration I will skip as less important for the consideration of the main topic.
Most often, we use performance and lifting as two parameters characterizing the essence of the pump work. Each hydraulic characteristics of the pump is a lifting curve in the performance function h = f (q) and usually has the shape of a parabola, at least in its main range.
Sample characteristics of the pump about QMAX = 350 l/min. and hmax = 25 m.
Maximum flow and pump efficiency?
Often talking to customers, they ask me about the maximum parameters of the pump, Qmax performance and lifting hmax (red dots on the chart). Of course, I give them these values, but I try to ask to what extent the pump will work. If the customer is unable to determine the parameters of the pipeline, i.e. the resistance that the pump must overcome, looking at the chart below, the only certain information is that the pump will have a performance in the range from 0 to 350 l/min (Qmax). So we don't know much. The selection is a bit blind, and the pump performance from its maximum flow can be very far away.
However, if the customer knows the parameters of the pipeline and determines them in a similar way as in the diagram:
It is with the help of simple mathematical calculations that we can determine approximate losses on the discharge pipeline and determine its characteristics. For example, the diameter of the PE50 pipe, Hg = 5m and L = 250 m.
If we apply these two characteristics on each other, we will get the expected working point of the QP/HP pump marked on the chart with a green dot.
Pump work point
Place of cutting the hydraulic curve of the pump with a loss curve on the discharge pipeline. Real, though only computing QP pump performance parameters when lifting HP. On this basis, we should choose pumps when buying new ones, but also when replaced from old to new ones. It should be remembered that each type of pump, from different manufacturers, even at similar values of Qmax or HMAX can give us completely different values of QP and HP. In fact, it is very rare for the XY pump to cover perfectly with the YZ pump. Personally, I know many cases that correctly collected data on the discharge pipeline allowed the user to replace the pumps with smaller, much more energy -saving while maintaining or improving the efficiency of the pressing.
Example A
PE90 pipeline, L = 500 m, Hg = 5 m Working point Qp = ~ 285 l/min. with hp = 9.5 m
Example b
PE50 pipeline, L = 400 m, Hg = 20 m Working point Qp = ~ 60 l/min. with hp = ~ 23 m
The above examples illustrate how much the parameters of the pump operation from its maximum parameters can differ from each other. That is why such important information is the data on the discharge pipeline, not Hmax and Qmax. The customer providing information that he is looking for a pump for e.g. 25 m and 350 l/min. Without adding that these are only maximum points talks about two different points on the characteristics of the pump. Therefore, he often hears that instead of a 1.5 kW pump at a price of 2-3 thousand (for example) he must buy a 4 kW pump for 7-8 thousand and resigned leaves to look for a cheaper and usually inferior quality alternative.
Consumer, do you want to have a well -chosen pump?
- Please tell us what deck pipeline do you have: diameter, length, height in the field?
- How many sewage would you like to press: what tank do you have, how many users?
- Are the pump parameters sought are maximum values or work point?
- The more data you provide to us, the greater the chance for your final success!