This contemporary photo shows one of the pair of steel clad guide rails mounted inside the pentagonal tower at the North end of shed 21 Wellington harbour.
Here one of the two ? (at least) accumulators that provided the constant pressure needed to run apparatus on the hydraulic power network, would have run down as demand increased and up as the pumps backed up the volume of water under pressure available. The drawings and specifications are yet to be researched but if it was like any other system, the WHB network would have had the pumps running so that the accumulators were at the top of their stroke for as much of the time as possible with excess pumped water being bled to waste as it's hard to start and stop or slow down a steam engine. The two accumulators simply took up the strain if/when the demand for water (volume) exceeded the pumping capacity. as the pressure in thenetwork remained pretty much constant, there must have been some device (flow metering or the position of the accumulator weight) which fed-back to the pumphouse and increased the pump speed or shut off or tightened up the bleed valve. Needless to say this was no rough and ready system, with big pumps, miles of pipes and dozens of cranes and winches and hoists and capstans, control would have been of paramount importance. By 1925 when Wellington had a reliable and high capacity 230v AC system in place, the hydraulic network may have been electric powered and thus more easily controlled. Anyhow, watch this space as more reliable and less speculative information is added!
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