A pressure gauge siphon, also known simply as a siphon, is a U-shaped tube installed between a pressure gauge and the process connection. It is commonly used in applications where the process fluid temperature is significantly higher than the acceptable operating temperature of the pressure gauge. The purpose of the siphon is to protect the pressure gauge from the high temperature of the process fluid.

Here's how a pressure gauge siphon works:

1. Fluid Dynamics: When a pressure gauge is directly exposed to a high-temperature process fluid, the elevated temperature can damage the internal components of the gauge, including the sensitive measuring mechanism and the sealing materials. Additionally, rapid temperature changes can cause the gauge to malfunction or fail prematurely.

2. U-shaped Design: A pressure gauge siphon consists of a U-shaped tube typically made of metal, such as stainless steel or brass. The siphon is installed horizontally between the pressure gauge and the process connection. The process fluid enters one leg of the siphon, flows through the U-bend, and exits the other leg, connecting to the pressure gauge.

3. Cooling Effect: The U-shaped design of the siphon creates a natural cooling effect by allowing the process fluid to expand and cool as it flows through the siphon. This helps to reduce the temperature of the fluid before it reaches the pressure gauge, protecting the gauge from exposure to excessively high temperatures.

4. Thermal Barrier: By introducing a length of tubing between the process fluid and the pressure gauge, the siphon acts as a thermal barrier, preventing direct contact between the high-temperature fluid and the sensitive components of the gauge. This helps to prolong the life of the pressure gauge and maintain its accuracy and reliability in high-temperature environments.

5. Selection and Installation: The selection of a pressure gauge siphon depends on factors such as the temperature and pressure ratings of the process fluid, the material compatibility with the process media, and the installation requirements. Proper installation, including ensuring a continuous flow path and proper orientation of the siphon, is essential to ensure effective cooling and protection of the pressure gauge.

In summary, a pressure gauge siphon is a simple yet effective device used to protect pressure gauges from high-temperature process fluids. By creating a cooling effect and acting as a thermal barrier, the siphon helps to maintain the accuracy and reliability of the pressure gauge in demanding industrial environments.