This problem occurred on an early model Coaster conversion done by Trakka. After 10 years or so the pump failed. It was replaced by a larger capacity unit as nowadays that is all that is available in 24 volt. After fitting it was found that the Whale taps fitted to the unit all developed an extremely irritating high pitched squeal when operated. The rig was presented to a couple of experts but all shook their heads!!! The simple solution was to fit one of those cheap irrigation inline pressure reducers into the discharge line. For good measure an irrigation stop cock was also fitted into the output line from the pump. This reduced the flow to a lower more acceptable level consistent with not running out of water tooooooooo quickly! Interestingly the Whale taps all worked perfectly after all this time and the washers did not need replacing.