The invention relates to a process water analyzer (10) for automatically analyzing parameters of a
water sample. Comprising a process
liquid storage tank (70, 72) having a process liquid (70 ', 72') wherein a process
liquid storage volume (V70, V72) in the
storage tank (70, 72) defines a storage liquid level (I70, I72) at a storage liquid level height (h70, h72), a metering chamber (30) fluidly connected to the process
liquid storage tank (70, 72) and fluidly positioned downstream of the process
liquid storage tank (70, 72), and a positive displacement
metering pump (20) fluidly connected to the process
liquid storage tank (70, 72) and fluidly positioned downstream of the process
liquid storage tank (70, 72). And a valve (30) fluidly connected to the top of the metering chamber (30), the
metering pump (20) is used for sucking the process liquid (70 ', 72') into the metering chamber (30), an
air cushion (27) is always vertically arranged between the
metering pump (20) and a metering chamber liquid level (I) in the metering chamber (30), so that a
liquid column (Ic70, Ic72) with an effective vertical
liquid column length (c70, c72) is provided between the storage liquid level (I70, I72) and the metering chamber liquid level (I), and the
air cushion (27) is used for sucking the process liquid (70 ', 72') into the metering chamber (30). The metering pump (20) directly sucks in a pressure-adapted gas volume (Vgas) of the
air cushion (27) having an air
cushion pressure (P) in order to pump a set process liquid volume (Vliquid) into the metering chamber (30), and wherein a process liquid
dose control unit (200) is provided in order to control the process liquid volume (Vliquid) in the metering chamber (30). The process liquid
dose control unit (200) provides a value of the pressure-adapted pumped gas volume (Vgas) as a function of the gas
cushion pressure (P) affected by the effective vertical
liquid column length (c70, c72).