Makes the gauge more robust.

I'll let WIKA explain it to you: (copied from their website)

Liquid-filled gauges are generally preferred over dry gauges for two reasons: performance and ROI. Liquid-filled gauges are filled with a liquid, usually glycerin or silicone oil and are designed to perform optimally in less-than-ideal conditions. While WIKA�s liquid-filled gauges are engineered to function in difficult environments, they�re also more economical from a long-term perspective: High heat, pulsation, or vibration lead to instrument breakdown, but WIKA�s liquid-filled gauges stand up to these harsh conditions.

Liquid Filled vs. Traditional Gauges

The primary reason for gauge failure is vibration. In traditional dry gauges, delicate links, pivots, and pinions are prone to damage from vibration, leading to inconsistent performance. In a liquid-filled gauge, the fluid fill effectively dampens system pulsation, making the gauge pointer easier to read.

Likewise, humidity and moisture pose problems for dry gauges. Condensation can make a gauge difficult to read or, in some cases, can cause failure due to icing. Liquid-filled gauges, though, are sealed to prevent internal condensation, and by keeping moisture out of the system, gauge movement is protected during icing conditions.

The choice of fill fluid is based on the application, but glycerin is typically used for room-temperature applications and silicone oil is commonly used for extreme temperature applications, especially when icing is a problem. An oil with insulating properties is ideal if the system has exposed electrical contacts.

Why Liquid Filled?

Liquid-filled pressure gauges offer a number of advantages over traditional, dry case pressure gauges:

Liquid-filled gauges have longer lives than traditional (non-hermetically-sealed) gauges because of their viscous fluid filling. Over time, this design advantage results in costs savings due to lowered instrumentation costs as well as lessened unscheduled downtime.
Internal liquids protect against severe temperature fluctuations and vibrations�major factors in the breakdown of regular gauges. Because they dampen temperature spikes and vibrations, WIKA�s liquid-filled gauges are easier to read, allowing for greater accuracy and process control.
In traditional gauges, condensation build-up results in visibility issues. This can be a crucial (and costly) flaw in high-humidity environments�an unreadable gauge is a worthless gauge. A solution to the impact of high humidity situations, WIKA�s liquid-filled gauges are designed to prevent moisture from entering not only the body casing but also the inside of the case lens.
Because they are sealed and constructed to meet rugged specifications, liquid-filled gauges are commonly used in highly corrosive chemical processes or in manufacturing or refining processes, and where products must be transported, stored, or handled in extreme temperature conditions.


Learned something new here. Use a silicone fluid for gauges that will encounter low freezing temperatures.

As far as how much oil, I know there needs to be a bit of air in there. The ones we got with the bottle had a predetermined measure with each gauge so just pour it in.

I also have a couple of expensive gauges that have a burp valve on top of the casing. That's to equalize the internal case pressure with atmosphere for a more accurate reading.

RC - Any indication of why the fluid level is becoming low?