On trucks and trailers, hydraulic pumps are driven either directly or indirectly by the truck engine. Power take-off (PTO) devices may be driven directly by the truck engine or from gearing in the transmission. Alternatively, electrical power produced by the truck electrical system can be used to drive electric motors located anywhere on either the truck or trailer chassis. For instance, a two-tier car transporter trailer can be equipped with extensive hydraulic circuits that often use several electric motors to actuate a number of independent hydraulic circuits.
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