19 September, 2019

Lee restrictors keep the electricity on

09 December, 2016

During a recent refurbishment of the Allt na Lairige hydro-electric power station near Inverary in Scotland, the hydraulic control system was upgraded from the original low pressure system to a modern high pressure one.

In-house designed multi-orifice restrictors were being used in the hydraulic actuators which operate the main water inlet valves, called spears, which are controlled by the governor to ensure that suitable control of the water jets to the turbines is ensured for all load conditions of the generator.

Increase in system pressure

Due to the increase in system pressure and the variation in temperature throughout the year which was affecting the viscosity of the oil, it was determined that the restrictors were not providing sufficient restriction, which resulted in sporadic operating times of the spears.

To compensate for this, adjustments had to be made to throttle the flow at the hydraulic power unit, since there were concerns about making the orifices smaller than 0.9mm diameter due to contamination.

Lee Products was able to solve the problem by providing high Lohm rate restrictors from its 250 series axial visco jet range.

Visco jets contain many internal stages to provide a very small restriction to flow, but still keep the internal passageway sizes large enough to resist blockage by contamination. Filter screens are fitted at each end of the visco jets to provide protection for the orifices. Another performance advantage of the visco jet is that, by continually swirling the fluid to maintain turbulent flow, it compensates for the change in viscosity of the fluid due to most changes in temperature.

This was an important factor at the Allt na Lairige power station because the temperature of the hydraulic oil varies considerably during the year, such that the water valves were opening too slowly in winter with cold oil and too quickly in summer when the oil was hot.

New challenge

Mike Stott, general manager at Lee Products Ltd., commented: “We’re delighted to be able to help the Allt na Lairige by helping to optimise the performance of the oil within the power station. We primarily supply our products to the aerospace, Formula One and oil tool sectors, so this project has proven our visco jet flow restrictors are also fit for purpose outside of our mainstream market segments. We have supplied a number of check valves and relief valves for industrial gas turbines for power generation stations; however, the Allt na Lairige project is more akin to an industrial hydraulic application. Following the success of this project we are currently seeking to secure further contracts with other hydro-electric power stations in Scotland.”


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