Abstract: A hydraulic booster is disclosed which includes a piston which is actuated by fluid pressure communicated into the booster working chamber from an accumulator by a spool valve. An operator actuated input rod generates fluid pressure in a control chamber when the booster is actuated. The pressure generated in the control chamber shifts the spool valve to a position admitting fluid pressure in the working chamber. An exhaust passage including a relief valve communicates said accumulator chamber with said control chamber. The accumulator includes a piston adapted to bias the relief valve into its open position when the fluid pressure level in the accumulator chamber is below a predetermined value.

Abstract: A hydraulic booster is disclosed which includes a control valve comprising a sleeve-shaped spool and a control piston slidably mounted at one end of said spool. The control piston projects into a control chamber filled with hydraulic fluid and in which are movable an operator-operated input member and an output member connected to a boost piston slidably mounted in a working chamber. The pressure generated in the control chamber shifts the control piston and the spool to a position admitting fluid pressure from a pump into the working chamber. The ratio of the effective areas of the control valve respectively submitted to the control pressure and to the pressure prevailing in the working chamber is about two.