Specialty Item Gauges
Gauges measure water level, discharge, velocity, temperature, pressure or vacuum within a piping system under both operating and non-operating conditions. Readings may be used to check the performance of pumping equipment and aid in the balancing of fluid flow through system components.
Gauges usually consist of a bourdon tube, rack and gear, and a pointer. The bourdon tube is a flattened oval metal tube which is bent into a partial circle. With one end of the tube fixed to the gauge case, the free end straightens as pressure is applied within the tube. A link, rack and gear on the pointer translate the motion of the free end of the tube to a rotation of the pointer. Depending on the service conditions needed, varying levels of accuracy and pressure ranges are available from manufacturers.
Several accessories are available and designed to provide more accurate readings, and in many cases, to protect the instrument from damage. A root valve isolates the pressure gauge from the contents of the piping system, enabling instrument removal, calibration, or replacement. Root valves are usually pet cocks or needle valves, but they may be any other desired valve that provides complete shut-off.
Impulse dampeners prevent wear on delicate gauge mechanisms by slowing pressure changes and reducing shock or chatter. They are installed between the instrument root valve and the gauge, where sudden pressure changes are noticeable. Snubbers prevent accelerated wear to the internal movement, and reduce shock to the gauge. They are installed between the root valve and gauge, where surging or oscillation is prevalent.
Coil siphons are commonly used on steam services to form a pocket of water between the root valve and the gauge to prevent steam from reaching the bourdon tube. Diaphragm seals can be used when the pipe line media is corrosive or contains suspended solids that could clog or solidify in the sensing element.