Overrunning loads induce forces into the speed reducer that can significantly shorten life. Heco speed reducers are typically driven by hydraulic motors that are connected inline with hydraulic relief valves to relieve pressure spikes in the hydraulic systems. In overrunning load conditions speed reducers are back-driven into the hydraulic motors which turns the motors into hydraulic pumps that create hydraulic system pressure spikes. Typically hydraulic cross-port relief or counter balance valves will relieve these pressure spikes.
Because of inefficiencies in the hydraulic motors being driven as pumps it can take 150% of the typical drive operating torque to back-drive a speed reducer/hydraulic motor and create enough pressure for the hydraulic system cross port relief or counter balance valves to react. This condition is prevalent in swing or slewing drives as well as ground power drives on mobile equipment.
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