Pressure gauges are very important instruments used in various plants and manufacturers to measure the pressure of gases or liquids within a contained environment.
Why is liquid filled in pressure gauges?!
A common question that arises is why liquid is filled in pressure gauges. The answer is multi-sided and involves understanding the role of liquid in enhancing the functionality and accuracy of pressure gauges.
1- Dampening Medium
Liquid filling in pressure gauges serves as a dampening medium to absorb the pulsations resulting from fluctuating pressures. These pulsations can cause oscillations in the gauge mechanism, which may lead to inaccurate readings.
By filling the gauge with a viscous liquid, the amplitude of these oscillations is reduced, ensuring a more stable and accurate pressure reading.
2- Protecting Parts
Liquid filling in pressure gauges can protect moving parts from corrosion and wear. The liquid serves as a barrier between the bourdon tube, the sensing element, and the internal atmosphere of the gauge. It prevents the ingress of moisture and other contaminants, which can cause corrosion, leading to reduced accuracy and shortened lifespan of the gauge.
In some cases, the filling liquid itself, such as silicone oil or glycerin, possesses lubricating properties that further preserve the mechanism's integrity.
3- Reduce the Effects of Vibrations
In applications involving vibrating machinery or environments, liquid filling reduces the effects of these vibrations. Without a dampening effect, the vibrations could cause the pointer to move erratically, making it difficult to obtain a precise reading.
The viscosity of the filling liquid provides a dampening effect that increases the gauge's resistance to these movements.
4- Temperature Compensation
The liquid filling in pressure gauges can also aid in temperature compensation. Fluctuations in temperature can cause the bourdon tube to expand and contract, leading to inaccuracies in pressure readings.
The filled liquid helps absorb heat, reducing the gauge's sensitivity to temperature changes. This is particularly important in industries where extreme temperatures can adversely affect instrument performance.
5- Diagnostic Tool
The liquid level acts as a diagnostic tool. Changes in the liquid level within the gauge may indicate a leak, demonstrating that the gauge or the system is no longer airtight. This can prompt users to service the gauge or address any system issues before they escalate to larger problems.
What is the Liquid in Pressure Gauges?!
Depending on the operation conditions, The most frequently used filling liquids in pressure gauges are typically Glycerine-water mixtures or Silicone oils.
Glycerine water is suitable for ambient conditions and low pressure whenever Silicone oil gauges are used for high(>60°C) or very low (<-20°C).
Note: If we supposed that the pressure gauge is not completely filled, the filling medium can absorb an additional water and expand, depending on the humidity and ambient temperature. So to allow for this expansion and to prevent the case of the gauge from leaking, the case is filled with liquid to only 80%-90%.
Why Pressure Gauges are Plugged at the Top Side?!
Pressure gauges are typically plugged at the top side to ensure that the liquid does not escape. When the gauge is filled with liquid, it is then sealed and a plug is inserted at the top to keep the liquid inside. This is essential for the gauge to function correctly, as the presence of the liquid is what allows the gauge to absorb vibrations and maintain accuracy.
Furthermore, the liquid helps to prevent the entry of moisture, dust, or other foreign particles that could interfere with the operation of the gauge.
Dry gauges Vs. liquid-filled gauges
Dry gauges and liquid-filled gauges both have their own advantages and disadvantages:
- Dry gauges are simpler and less expensive, as they do not require the liquid filling process. They are also lighter and can be used in applications where the added weight of the liquid would be a disadvantage. However, they are generally less accurate than liquid-filled gauges and are not as resistant to damage from vibrations.
- Liquid-filled gauges, on the other hand, are more accurate and durable, but also more expensive and heavier. They are ideal for use in environments with high levels of vibration or where accuracy is critical.
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