Whether two small pumps are better than a single large one: In this consideration of many users, it depends on the application - and a specific component.
Tsurumi, the market leader in dewatering pumps in the construction industry, points out that various aspects speak in favour of two or more small pumps in applications with dirty water. In some cases, one large pump is too much of a good thing.
If the distances are short, only one adequate pump is needed. If the distance to be covered exceeds its capacity limit, a second pump can be connected via an adapter. This is called booster operation: the second pump increases the possible total length of the water pipe.
Many pump operators do not know that this option exists at all. Moreover, it is relatively easy to realise.
Theoretically, the number of pumps that can be operated in series is unlimited. Significant capacity losses are not to be expected. With two identical pumps, the achievable distance performance is roughly doubled. However, the flow rate remains the same. If one wanted to increase this, parallel operation of the pumps is necessary or the use of larger models.
Key factor flexibility
Small pumps connected in series offer the advantage that the individual pumps can be moved more quickly due to their relatively low weight, they are easier to replace and can be better maintained or repaired. There are practical advantages in terms of spare parts logistics and capital requirements, too.
Two pumps can be connected directly one after the other. Alternatively, they can be spaced so that, for example, one pump is positioned every 30 metres. Whether the piping is fixed or with flexible hoses is functionally irrelevant. There are also advantages during dismantling.
Dewatering with large pumps is particularly interesting because the entire system consists of only a few components.
This is attractive, considering the potential problems of an extensive small unit configuration. That comes with the core risk of all complex systems: (Too) many components are involved, they may not be in the best condition, they may not be set up optimally or they simply should not have been combined in the first place.
Space requirements as a bottleneck
However, a solution with a powerful unit like the multi-stage high-pressure pump LH4110W, the manufacturer's top model with a delivery head of 216 m, has to be realised first: such a pump weighs about 1.3 tonnes when dry. Also, the use of these big guys only makes sense if their performance is needed from the very beginning.
The reliability of the system must also be taken into account: if the only large pump fails, the entire dewatering system stops. However, this also applies to the chain solution if a link fails - no matter how small. But getting a large pump going is likely to take longer.
In some cases, however, the question does not even arise. If sheer performance with high throughput is required, for example in open-cast mining, there are hardly any alternatives to large-scale equipment.
On the other hand, the space available underground or in tunnelling is often so limited that there is simply no room for a large pump: After all, vehicles, mining machines and people still have to be able to move accident-free in the narrow veins. Often there are not even intermediate basins for pumping in the roadway sections, so that only a slim solution is available for dewatering. A similar problem arises with deep bore holes or in the waste water sector of industry and municipalities.
The booster adapters are available from Tsurumi Europe in Düsseldorf, Germany, as a standard component at a comparatively low price. Operators of dewatering pumps should therefore first consider connecting them in series if necessary. As a rule, different pump types may be combined. The adapters can thus continue to be used if other, larger pumps are purchased later.
What a pump is actually capable of is stated in the data sheet. Every pump unit has an optimum operating point. Two essential factors determine the performance of a pump: the maximum flow rate indicates the highest possible throughput under ideal conditions. Usually 15 degrees Celsius outside temperature, a homogeneous medium and horizontal pumping are defined. Which already describes the second factor, the maximum delivery head: the greater the slope or distance, the higher the power required. If pumping is to be vertical, the pump must not only bear the weight of the water column, but also generate flow velocity so that the pump sump empties. The specific weight of the pumped medium and its viscosity also play a role.
The booster adapter is a passive component that is quickly mounted: unscrew the swash plate at the bottom of the first pump, replace the series screws with new double bolts, put on the adapter, screw it tight, and connect the second pump or hose there. A video on Tsurumi's Youtube channel shows how easy the assembly is.