Abstract: A system for varying the deadweight of apparatus incorporates a fluid coupling (10) and fluid flow control valve. The fluid coupling comprises first and second connectors (20, 30) each configured for attachment (at respective ends 21 and 31) to respective fluid conduits (not shown), for example hydraulic hoses. Each connector (20,30) has a cylindrical body (3,3) configured to rotate about the longitudinal axis A having a bore or lumen (22,32) for fluid flow therethrough in a predetermined orientation as indicated by arrows D. Registration of the respective lumens (22,32) at ends (23,33) of the connectors permits fluid to flow between the connectors (20,30) at maximum rate when lumens (22,32) are aligned with apertures (24?,34)? , fluid to be stopped when lumens butt against shutters (24,34), and fluid to flow at intermediate rate when lumens are registered in intermediate positions.