Disclosed is an accumulator for use on hydraulic brake systems. The accumulator includes a housing, a pressurization cap which is threadably connected into the housing and a resilient bulb contained within a volume between the housing and pressurization cap. The resilient bulb provides a flexible volume which can expand in response to high pressure surges and shock waves experienced by the braking system. The bulb is contained primarily within an interior cavity formed in the pressurization cap. The resilient bulb is constructed in a size and shape which causes an annular volume between the bulb and pressurization cap to be pre-pressurized when the accumulator is assembled together. The accumulator is also provided with a particularly effective sealing arrangement to prevent leakage of air and hydraulic fluid from around the bulb.