What does the term displacement mean? What does flow, immersion or suction depth mean?

Different pumps have different parameters depending on their design and purpose.

To pump water from a certain depth, it is necessary to know the maximum displacement of the pump. This value indicates to what height the pump is able to pump the water. However, it is always necessary to allow for a margin above the stated displacement, as this value is a limit and when the maximum displacement height is reached, there will be virtually no pressure at the end of the pipe to transport the water anywhere. For example, if a vibrating pump is quoted as having a displacement of 70 m, it couldn´t be used in a borehole about 70 m deep. Some frictional losses have to be added - the calculation of frictional losses is complicated, the diameter, length and material of the hose/pipe have to be included, the average water temperature etc... Really very roughly, we can calculate an average of about 1 meter of displacement loss for every 10 m of pipe or 1/2" of hose. Additional pressure is then required to ensure that the water flows at the end of the system at a sufficient pressure and velocity for the desired purpose. If you intend to use the pump to pump water into the house, to drive irrigation systems and so on, it is always better to consult with a specialist. The maximum displacement of a pump is always indicated by the height difference between the water level and the mouth of the hose or pipe. For submersible pumps, it does not matter how deep the pump is submerged. For surface pumps, it is inclusive of the suction depth.

The maximum pump flow is then the value of how much water the pump can pump under ideal conditions. This value is usually given in litres per hour. This value is again rather approximate, the actual flow rate depends on how the pump is used. The same pump will pump water at a different rate depending on the length and diameter of the pipe or hose, the flow rate is also significantly affected by the height to which the water is pumped. If a pump is quoted to have a maximum flow rate of 7500 l/hr (for example), you will probably never achieve this flow rate in normal use. The pump is designed to achieve under ideal conditions and this figure can only be used for calculation purposes, where the actual flow rate will be affected by the diameter and length of the hose or pipe and the elevation to which the water will be pumped.

For submersible pumps, the maximum immersion depth is often specified. This value gives us an indication of the depth to which the pump can be safely submerged. Submersible pumps contain electrical drive systems that are hermetically sealed so, that water cannot penetrate them. Naturally, as the immersion depth increases, the ambient water pressure also increases and the immersion depth value is derived from the maximum pressure that the pump can safely withstand on a permanent basis. Water pressure could penetrate the watertight parts of the pump at greater depths, while damaging them or causing a short circuit.

The maximum suction depth is then specified for surface pumps. Surface pumps are positioned above the water level at the surface and draw water through a suction line or suction pipe. The maximum suction depth means the maximum value of the difference between the pump height and the water level. If a surface pump is purchased for pumping from a well or sump, for example, the suction depth must be based on the minimum level, i.e. the maximum level of the sump or well and the position of the pump. A conventional surface pump can effectively pump water from a maximum depth of 8 m, according to the laws of physics.