Liquid leak detectors sense when a liquid is leaking from a pipe, tank, or other receptacle. With most liquid leak detectors and fluid monitoring systems, an audible alarm or visual indicator alerts personnel based upon an accumulation of liquid, pressure difference, or change in flow. When selecting liquid leak detectors, leak detection method is the most important parameter to specify. Detectable liquid types, liquid features, detector features, and output options are also important considerations. Water, corrosive fluids, and petroleum-based products are examples of detectable liquid types. Detectable liquid features include foam or bubbles, dirty liquids, and opaque liquids.
There are many different types of liquid leak detectors. Devices that rely upon electrical conductivity or resistance use a low-voltage applied across separate electrodes. Liquid leak detectors with electrochemical sensors output an electrical signal, but use a selective chemical sensor. Mass balance leak detection devices or flow metering is based on the difference between inflow and outflow meters. Mechanical float switches or relay contacts use sealed reed switches in a stem with a permanent magnet installed in the float. As the float rises or falls, a switch is activated. Mechanical line leak detectors are also available. These fluid monitoring systems use pressure sensing, a piston operated valve, or pressure vacuum switch to indicate leakage in pressurized piping systems.
Liquid leak detectors include optical leak detectors, positive pressure devices or vacuum sensors, and ultrasonic leak detectors. Optical leak detectors use optic sensors and optical refraction to detect the presence or absence of fluid. Often, light emitting diodes (LEDs) are used as the light source. Positive pressure sensors or vacuum sensors are designed to detect pressure changes in the interstitial space of double-walled tanks. Ultrasonic leak detectors are also available. These liquid leak detectors use mass and/or microviscosity alterations of acoustic wave propagation. They detects the ultrasonic noise created by gas moving through a small orifice, or recognize the attenuation and dielectric properties of the liquid or air present (piezoelectric SAW devices).
Output options and detector features should be considered when selecting liquid leak detectors. There are four choices for output options: analog voltage, analog current, frequency or modulated frequency, and switch or alarm signal. Some liquid leak detectors are equipped with features such as built-in alarm indicators and discriminating or selective sensors. Others are intrinsically safe (IS) or submersible.