Liquid-filled pressure gauges offer exceptional protection from vibration and shock and are the preferred choice in most high physical stress process environments. When selecting and installing liquid-filled pressure gauges, it’s important to keep a few facts in mind. First, make sure the gauge is filled with the appropriate liquid for the application. (Glycerin or silicone cannot be used as a liquid fill for gauges in applications where strong oxidizing agents are present.) Second, most liquid-filled gauges must be vented before use so they read at local atmospheric pressure.
Liquid-filled pressure gauges provide a number of advantages:
- The liquid absorbs vibration and pressure spikes
- The dampening action of the liquid enables the operator to take readings during conditions of rapid dynamic loading and vibration
- The liquid lubricates all moving elements, dramatically reducing wear in the movement
- Because most liquid-filled gauges are filled with non-aqueous liquid and hermetically sealed, they perform in corrosive environments and are immune to moisture penetration and icing and shock effects are lessened.
Liquid-filled gauges enhance the reliability and integrity of the measuring system for long periods under extreme operating conditions.
Allowable Ambient Temperature Ratings:
Temperature range in which the operation of the gauge is not adversely affected by the filling liquid. At temperatures above the maximum rating, the fluid may break down. At temperatures below the minimum rating, the fluid may solidify (freeze).
- If icing is a problem, use gauges filled with silicone oil or other comparable liquids. They have low viscosities even at -60C
- If the system has electric accessories, such as contacts, use insulating oils
- If extreme temperature fluctuations are expected, use silicone oils
The higher the liquid viscosity, the greater its dampening capacity. The reason for this is that dampening changes in proportion to the temperature-dependent viscosity of the filling liquid. The suitable degree of dampening depends on the operating requirements the gauge must meet, such as pointer response time, pressure extremes, vibration and changes in pressure. WIKA can recommend specific liquids to suit problem applications.
Liquid-filled gauge case venting
For pressure gauges with full scale ranges of 300 psi and below (including vacuum and compound ranges of 30″ Hg-0-200 psi and below), case venting (after the gauge is installed) is necessary to preserve the accuracy. Temperature fluctuations during shipment and in the process application cause the liquid filling to expand and contract which in turn increases or decreases case pressure. As a result, accuracy can be decreased and the pointer may not return to zero properly until the gauge is vented to the atmosphere.
To vent a WIKA gauge, move the valve to the open position which will release any pressure or vacuum built up in the case. If the gauge is installed in an upright position, the lever can be left in the open position. The lever allows the use of a gauge in a non-upright orientation.