A valve arrangement for accurately controlling the bleed rate of a sphygmomanometer. The valve includes a head mounted for movement between closed and open positions, with the open position being established by the setting of a cam element which is contacted by the head when the valve is opened. Contact between the head and the cam permits the air under pressure to escape from the sphygmomanometer either at a uniform rate (if the head-cam contact is maintained continuously) or in discrete controllable quantities (if the head is periodically brought into contact with the cam). The cam position is pre-settable to establish a range of release rates. The valve arrangement also incorporates an improved inverted conical release valve and seat.