SOLVIA PumpFlow is a system for the control of the delivery of a submersible grinder pump at sewage pumping stations and receiving tanks. The flow sent into the sewer is set by the share returned to the tank through a recirculation line, while the pump and its cutting mechanism run at their rated speed of rotation.
Sewage pumping stations, receiving tanks, balancing tanks and package treatment plants pump wastewater that carries solid and fibrous matter: rags, textile fibres, sanitary articles, fragments of polymer, food residues. A submersible grinder pump breaks such matter up at the entry to the wetted parts, so that it blocks neither the pump nor the pressure pipeline. The cutting mechanism manages that only at a high speed of rotation.
The delivery of such a station is rarely steady: the inflow rises in the morning and in the evening, falls at night and grows sharply during a shock discharge. The development sets the delivery required into the sewer without touching the speed of the pump: part of the flow leaves the pressure line for a recirculation pipeline and returns to the receiving tank through a nozzle below the liquid level. That return does no idle work — it mixes the tank.
Two habitual ways of changing the delivery of a pump are used in sewerage. Throttling holds the flow back with a valve on the pressure pipeline and creates hydraulic losses that are paid for in electricity. Variable-frequency control lowers the speed of the motor, and for an ordinary pump that is usually acceptable. On a grinder pump the speed of the cutting mechanism falls together with the speed of the shaft, and it is that speed which decides whether fibres are cut or wound.
The failure then unfolds as a chain. A lower speed of rotation worsens the grinding of fibres, causes them to wind around the cutting mechanism and leads to a loss of delivery, an overloaded motor and an emergency stop. After the stop come the lifting of the pump out of the tank, manual cleaning and the downtime of the station. The flow control for the sake of which the speed was lowered costs more than the uneven inflow it guarded against.
The grinder pump stands in the receiving tank and feeds the wastewater into a pressure pipeline carrying shut-off and control valves that set the delivery into the sewer. Between the outlet of the pump and those valves a recirculation pipeline is connected to the pressure line, and its other end is led into the inner volume of the tank. On it stands a regulating element that changes the quantity of liquid returned, and its outlet section carries a nozzle below the level of the wastewater.
Control comes down to the division of one and the same flow between two paths. When less is to go into the sewer, the element on the recirculation opens wider and the greater part of the flow returns to the tank; when more is to go, the recirculation is reduced. The pump stays in the region of its rated duty, and the speed of the cutting mechanism does not change at all — that is what sets SOLVIA PumpFlow apart from a variable-frequency drive.
From throttling the split differs in the fate of the diverted part of the flow. A valve kills it on resistance, and the energy goes into losses, giving the tank nothing. Recirculation returns that part to the receiving tank and spends it there, so the share of flow taken off the delivery into the sewer turns not into losses on a valve but into hydraulic work inside the tank.
The nozzle sits below the minimum working level of the liquid and forms a directed high-velocity jet. The jet creates circulation in the volume of the tank, stirs up the sediment on the floor and, by an ejection effect, draws the surrounding liquid into motion. In the patent claim the nozzle may be oriented towards the floor of the tank at 15–45 degrees to the horizontal plane, and the particular angle is settled when the configuration is chosen for the tank.
Sediment, fats, fibrous matter and heavy particles gather in receiving tanks; where mixing is poor, deposits form on the floor, odours appear and the balancing of the wastewater gets worse. An ordinary bypass line returns the flow to the suction of the pump or guards it against running on a closed valve, yet it does not mix the tank. Here the return is directed into the volume of the tank, and the recirculating flow itself does part of the mixing.
The regulating element on the recirculation line comes in manual and in automated form. In the automated one it is driven by signals from level sensors in the receiving tank and pressure sensors on the pressure pipeline: a rising level is answered by a greater delivery into the sewer, a limit on the discharge into the pressure line by the return of a greater share of the flow, and a need for mixing by more recirculation. The pump stays at its rated speed in every regime.
The worked example given by the developer is a sewage pumping station of 50 m³/h with a receiving tank of 15 m³, a pump of 2.6 kW rated at 2900 rpm, a pressure pipeline of DN80 and a recirculation line of DN50. The nozzle is narrowed to DN25, set 0.3 m above the floor and oriented at an angle of 30 degrees.
With the return fully open the flow goes back into the tank in its entirety and gives intense mixing, while under partial control the delivery into the sewer holds within a range from 5 to 50 m³/h and the speed of the cutting mechanism is kept at 2900 rpm. Over 12 months of operation no case of blockage or of fibre winding was recorded at that site. This is one particular execution, not a guarantee for an arbitrary station.
SOLVIA PumpFlow is SOLVIA's own technological development in the field of pumping systems for sewerage; it has patent protection in Russia. The solution brings together a submersible grinder pump, a pressure pipeline with shut-off and control valves, an adjustable recirculation line, a nozzle for directed mixing and control by level and by pressure; it is applied both in the building of new stations and in the modernisation of existing receiving tanks. The particular parameters of the recirculation pipeline, of the nozzle, of the regulating element and of the control algorithm are chosen for the site.
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