Hydrostatic pressure sensing switches for activating switch contacts at preset liquid level thresholds.
A hydrostatic liquid level switch is an instrument for monitoring the height of a liquid and tripping a relay contact switch or transmitting a solid state relay switch output when a maximum, minimum or intermediate level has been reached. The hydrostatic liquid level switch output can then be utilised by other instrumentation to open a valve, illuminate an warning lamp, activate an audible alarm, or switch on/off a pump.
Food grade level switch with indicator for 1 metre tanks - Food-grade level switch and LED indicator for tanks up to 1 meter high. PNP contact output, adjustable threshold, 316L stainless steel diaphragm. Ideal for food and beverage applications.
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Hydrostatic pressure liquid level switches are threshold contact trip devices which typically consist of a pressure switch or a pressure sensor incorporating a solid state NPN/PNP switch.
All liquids which are under the influence of gravity generate a hydrostatic pressure. This pressure is similar to the weight of a solid object, but because of the fluid state it is possible to measure how the weight of the liquid varies with height.
The resulting pressure at different heights is directly proportional to the weight of a liquid between the surface and a specific height point. The weight of the liquid can be derived from the mass and force (gravity). The mass can be derived from the density and volume of the liquid. The volume of a liquid can be derived from the dimensions of the vessel containing the liquid. If the vessel has a fixed length and width, then the height is directly proportional to the volume, mass, weight and therefore the pressure.
Hydrostatic liquid level switches continuously monitor the variation in level to detect when a threshold has been reached. A hydrostatic liquid level switch is mounted on the outside of a vessel or tank using a threaded port, bolted flange, or clamped seal.
For installations where it is not possible to access the outside wall, there are hydrostatic liquid level switches which are sealed with a submersible rating so that they can be positioned by lowering them into the liquid.
Advantages
- Easily fitted at ground level to any port or take off, which is also convenient for maintenance
- No protrusion inside vessel
- Not affected by any surface disturbances such turbulence, foaming, vibration
- Small compact sizes possible
- Multiple switch contacts in one device
- Compatible with conductive or non-conductive fluids
- Flush diaphragm types prevent clogging and works with thick liquids and slurries containing solids
Disadvantages
- Pressurised or vacuum sealed vessels require two sensors or a differential pressure sensor with a more complex installation
- SG or density change affects calibration
- Flush diaphragm types vulnerable to mechanical damage from debris, cleaning processes
- Requires regular calibration due to gradual error shifts
- Installed in a position below the lowest required liquid level
- Fittings must be leak tight
- Diaphragm movement vulnerable to clogging, wear and tear
- High cost