A hydraulic-driven swing tube piston pump is normally equipped with two cylinders that move in opposite directions – one in suction and one in discharge. During the switchover from suction to discharge, the slurry discharge flow stops. During this time, the swing tube transfers from one cylinder to the other, and the hydraulic flow is diverted.
When the flow stops and starts again, the pressure drops abruptly and pressure spikes occur in the discharge slurry pipeline, causing high fluctuating loads and hydraulic hammering. This requires slurry pipeline reinforcements and additional supports, which requires additional investment costs. Also, the power drawn from the hydraulic power pack’s main motors fluctuates. This can result in a higher motor power rating and electrical system. On some occasions, the existing power supply system cannot handle these electric power fluctuations.
To reduce pulsations, a pulsation dampener can be installed in the discharge line. This dampener will supply slurry during the switchover of the pump, balancing the overall level of pulsations. Operators can choose to utilise either a nitrogen-charged dampener or a separate hydraulic-driven dampener, the latter performing somewhat better. These dampeners cannot prevent the pump from experiencing power fluctuations drawn from the main motors and will not reduce the discharge pressure pulsation level sufficiently.
To eliminate these power fluctuations, the following unique working principle has been developed: during the discharge stroke of one of the main cylinders, an additional flow above the nominal slurry flow is generated. This additional flow is sent to a third cylinder and absorbed. The hydraulic oil flow from this third cylinder is then transferred back to a hydraulic pump, which is mounted on the same motor shaft as the other hydraulic pumps and used for controlling the slurry cylinders. The additional energy required to move the third cylinder is fed back to the same motor shaft, so the only energy losses are friction and efficiency. During the swing tube switchover, the third cylinder will discharge the accumulated volume to the slurry pipeline, and thus continue the nominal pump discharge flow.
The third cylinder starts to build up momentum when the main slurry piston is slowing down to generate a theoretically smooth switchover from one cylinder to another. Due to the constant nominal flow, pressure fluctuations in the pump discharge line are reduced to a minimum level. Due to the energy recovery from the third cylinder during its suction stroke, fluctuations in power consumption are minimised to the level of friction and efficiency loss of the hydraulics of the third cylinder. A non-return valve is installed in the main slurry line directly after the pump to prevent backflow from the third cylinder to the pump.
Keywords: hydraulic-driven swing tube piston pump, pulsation-free
Vlot, E & Keijers, R 2018, 'Pulsation-free hydraulic-driven swing tube piston pump', in RJ Jewell & AB Fourie (eds), Proceedings of the 21st International Seminar on Paste and Thickened Tailings
, Australian Centre for Geomechanics, Perth, pp. 195-204.
Mainville, P 2017, ‘Pulsations from positive displacement pumps’, Proceedings of the 12th International Symposium on Mining with Backfill, Society for Mining, Metallurgy and Exploration Inc., Englewood.