trated in the accompanying drawings, in whichFIG. 1 is a longitudinal section through an hydraulic booster; andFIG. 2 is a longitudinal section through a further hydraulic booster.The booster of FIG. 1 has a housing 1 provided with a longitudinal stepped bore 2, an inlet 3 for connection to a source of high pressure hydraulic fluid, suitably anaccumulator 63 and an outlet 4 for connection to a res