|High-pressure pumps, such as the S500 from RMI, provide hydraulic power to the roof support systems.|
The efficient operation of the longwall roof support system directly affects the safety and productivity of the mine; any downtime on the system in such a difficult operating environment would be counter-productive. The reliable performance of these systems is essential if the mine is to maximize output and see a return on investment.
Due to the high pressures required to operate the roof support structures, the pumps use a reciprocating piston principle, usually powered by a mid-sized electric motor. A reciprocating pump discharges liquid by changing the internal volume of the pump and uses non-return valves (NRVs) at both the inlet and outlet ports of the pump. Typically, these pumps can produce 1,000 bar in pressure, in this application they will typically be operating at around 350 bar.
The major benefit of the reciprocating pump is that it produces a fixed volume of fluid displacement at a given speed and provides a constant flow, regardless of pressure. This fundamental design is beneficial to control the pumps by a variable speed controller, which allows accurate control of the output pressure. For applications requiring increased flow rates, one or more pumps can be added in parallel to the original to produce the desired flow rate at the same pressure rating.
It is important that the pump design incorporates the necessary safety features, including a safety relief valve to protect against a dead-head situation, when the system demand for flow has stopped, causing the pressure to rise instantly. The safety valve should be designed to allow the entire pump capacity to flow, while the opening point should be set at 10% above the operating pressure. In addition, the pipework associated with the safety relief valve should be properly sized to ensure adequate flow conditions.
For high-pressure applications, reciprocating pumps offer additional benefits as the design offers greater mechanical efficiency, which means that a smaller prime mover can be used and less energy is consumed. By carefully selecting the correct motor and matching it to the pumping system, a more efficient combination can be created, resulting in lower total cost of ownership.
Achieving an efficient design is one thing, but making it reliable for a mining application as well requires a higher level of development. This requires a certain degree of “over-engineering,” using materials and design concepts that may exceed the original specification, but which will afford a much greater level of reliability. In heavy industries, such as mining, building something to last can make the difference between catastrophically expensive downtime and ultimate profitability.
RMI Pressure Systems supplies reliable high-pressure pumping systems. The company also has a policy of continuous development of energy efficient products, which has led to the introduction of the ODIN (On Demand Intelligence) control system. This system uses a range of data supplied from equipment used in the process of longwall mining and uses it to calculate the changes in demand for hydraulic fluid before they occur. In this way, ODIN can modulate the pump speed and change the flow and pressure characteristics to meet demand in the most responsive way possible.