A Manometer is a device for measuring pressure. The international unit of measurement for pressure is the Pascal (Pa). In technical applications, however, the units “bar” or “pounds per square inch” (psi) are in more common use, whereby 100 kPa = 1 bar = 14.504 psi. Manometer readings always indicate an overpressure relative to an ambient pressure, which is usually 1 bar. A reading of 0 bar, therefore, means 0 overpressure, or an absolute pressure of 1 bar.
The quality and reliability of pressure measurements are of outmost importance for the safe and trouble-free operation of a brewery. Manometers are employed, therefore, at several stages of the beer-making process. They measure liquid pressures in piping systems; CO2 pressures in fermentation and lagering tanks; air pressures in pneumatic valve systems; differential pressures during lautering; steam, glycol, water, and gas pressures; beer pressures in dispensing systems; and absolute and differential pressures at the bottling line. They can also determine volumes indirectly by means of pressure transducers. High-quality manometers are especially important during filling to avoid potentially hazardous overpressures or inaccurate CO2 levels in the finished beer.
Modern brewery manometers are usually spring-loaded devices in round, copper alloy, plastic, or stainless-steel housings. The pressure-sensing element may be a Bourdon tube, a diaphragm, or a capsule element. Pressure sensors can also transmit signals to remote devices. They acquire such signals via resistance variations by the piezoelectric effect, strain gauges, or capacitance/inductance measurements, such as by ceramic capacitor. The simplest type, used in many craft brewing setups, is a set of two sight glasses on the lauter tun. One has an inlet above the false bottom, and the other one has an inlet below. Looking at the liquid levels in each tube, the brewer can gain a sense of the differential pressure across the grain bed and adjust the lautering accordingly.