Comparison Grundfos SQ 2-55 vs Speroni SPM 50-14

The maximum head is the maximum height to which the pump can raise water during operation (the highest height of the water column that it can support). This parameter describes the pressure created during operation, but since the operation of well pumps is directly related mainly to lifting liquid to a great height, it is easier to use head data in metres than pressure data. However, if necessary, one can be easily translated into another — 10 m of pressure corresponding to a pressure of 1 bar.

When choosing a pump for this parameter, it is not necessary to chase a large pressure, but it is necessary to take into account several factors.

The first of these is the actual height to which the water must be raised; it can be determined by adding the immersion depth of the pump and the height of the highest draw-off point above the ground. The immersion depth is displayed taking into account the so-called dynamic water level in the well — i.e. distance from the surface of the earth to the water surface during continuous operation of the pump (this indicator is greater than the static level, since when the water is pumped out, its level decreases). The dynamic level is usually indicated in the well passport; the pump should be at least a metre deep underwater, plus a margin of 2 – 3 m should be taken as an adjustment for seasonal level fluctuations. Accordingly, for a well with a dynamic depth of 40 m, supplying a house with...an upper draw-off point of 6 m above the ground, the total height difference will be at least 40 + 6 + 4 = 50 m.

The second point is the hydraulic resistance of the system. Even with horizontal pipes, pressure is required to move fluid through them; usually, when calculating, it is assumed that for every 10 m of the pipeline, 0.1 bar, or 1 m of head, is required. For a water supply system inside an average house, resistance losses are about 5 m of head (0.5 bar). Accordingly, if in our example the house is located 10 m from the well, then the margin to overcome the resistance should be at least 1 + 5 = 6 m of head.

And the third point is the pressure at the points of water intake because the pump must not only “push” the water to the tap, but also provide pressure at the outlet. Here, the optimal values may be different depending on the situation. For example, let's take at least 1 atm (1 bar), which corresponds to 10 m of pressure.

Thus, in our example, the pump head must be at least 50 m (height difference) + 6 m (resistance) + 10 m (outlet head) = 66 m. Of course, this is a calculation for the most general case; in special situations, the formulas may differ, so it makes sense to refer to special sources for them.

The highest pressure that can occur in the line when the pump is running. Note that usually we are not talking about normal working pressure (it is described by max. head, see above), but about short-term jumps that can significantly exceed standard values. The water supply system to which the pump is connected must normally tolerate not only standard values but also the mentioned jumps — otherwise, an accident may occur. Accordingly, the maximum working pressure is useful for assessing how the safety factor of pipes, fittings and other elements of the system corresponds to the characteristics of the pump.

The greatest depth under water at which the pump is capable of operating normally.

The optimal location for the deep well pump is as close to the bottom as possible (no closer than 1 m, but this margin can be ignored in this case). It is worth choosing according to the maximum depth, taking into account the depth of the well and the static water level in it (the distance at which the water mirror is located from the surface of the earth when the pump is turned off). For example, there is a well 50 m deep with a static level of 20 m; thus, the depth to the bottom is 50 – 20 = 30 m, and if you want to lower the pump to the very bottom, the maximum immersion depth must be at least 30 m — otherwise too high water pressure may damage the unit.

The largest amount of mechanical impurities in the pumped water, which the pump can handle normally. When used with dirty water, this parameter should be taken into account along with the maximum particle size (see above): if the impurity content is too high, the pump may fail even if the individual particle size does not exceed the norm.

The highest suction water temperature at which the pump can operate normally. For deep well pumps, the water temperature is also important because the pump is constantly immersed in water during operation, and the liquid provides cooling. Therefore, in modern models, performance indicators are usually low — less than 30-35 °C. However, the temperature in artesian wells, usually, is much lower (the only exceptions are regions with thermal waters, but specific equipment is used there).

The power consumed by the pump motor during operation. A more powerful engine can provide more head and performance, but these parameters are not directly related: two models of similar power can differ markedly in practical characteristics. Therefore, this parameter is secondary, and more or less unambiguously it describes only the class of the unit as a whole — powerful engines are typical for high-end performant models. But what this characteristic directly affects is the actual power consumption; and with it, in turn, are connected not only to electricity bills but also connection requirements.

The length of the standard power cable provided in the design of the pump.

Ideally, the length of this cable should not be less than the maximum immersion depth — this will ensure maximum ease of connection: the connection point of the cable to the mains will be above the water (in the best case, even outside the well), and you will not have to worry about insulation. At the same time, for several reasons, many pumps are equipped with rather short cords — about 1.5-2 m, and not long cables; in such cases, it is necessary to use special waterproof equipment.

The protection system guards the automatic shutdown of the pump in the absence of the pumped water. Water is involved in the removal of heat, works as a lubricant and creates a load on the pump motor. Working idle, the elements of the pumping station overheat and deform, which leads to premature equipment failure.

To avoid overheating of the engine, deep well pumps are equipped with a special thermal relay. When it detects a heating temperature above the norm, it automatically turns off the motor, preventing it from failing.