Loaded operation : A rise in suction pressure causes needle valve to close. Oil pressure in the power element increase as the oil enters capacity control circuit from the oil pump. Power element piston is forced upwards , pivoting lifting fork downwards . Lifter pins drop allowing suction valve to seat & load control the cylinder. Unloaded operation : A drop in suction pressure causes the needle valve to open. Oil bleeds through the valve to the crank case decrease the oil pressure in the power element, hence the piston moves downwards. lifting fork is pivoted upwards moving the lifting pin upwards. Suction valve is raised from its seat & controlled cylinder is unloaded.