A siphon tube (also called a pressure gauge siphon or pigtail siphon) is a coiled or looped tube installed between a pressure gauge and the process line. It serves critical functions in protecting the gauge from damage caused by high temperatures, pressure surges, and corrosive media.
Key Reasons for Using a Siphon Tube
1. Protects Against High Temperature
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Problem: Steam, hot gases, or high-temperature liquids can damage the pressure gauge’s internal mechanism (Bourdon tube).
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Solution: The siphon tube cools the medium before it reaches the gauge by:
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Creating a condensate trap (in steam applications).
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Allowing heat dissipation through the coiled/looped design.
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2. Prevents Pressure Surges & Pulsation Damage
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Problem: Rapid pressure spikes (water hammer) or pulsating flows can fatigue the gauge.
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Solution: The siphon tube dampens surges by:
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Acting as a buffer zone that absorbs sudden pressure changes.
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Reducing pulsation effects in systems like reciprocating pumps.
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3. Blocks Corrosive/Dirty Media
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Problem: Slurry, corrosive fluids, or particulate-laden gases can clog or corrode the gauge.
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Solution: The siphon:
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Traps condensate (in steam systems), preventing direct contact with hot/corrosive steam.
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Allows sediments to settle instead of entering the gauge.
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4. Maintains Gauge Accuracy & Longevity
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By stabilizing temperature and pressure, the siphon extends the gauge’s life and ensures consistent readings.
Common Applications of Siphon Tubes
✔ Steam Lines (Boilers, HVAC, power plants)
✔ Hot Liquids (Oil, chemical processes)
✔ Pulsating Systems (Reciprocating pumps, compressors)
✔ Corrosive/Dirty Media (Slurry, gas pipelines)
Types of Siphon Tubes
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Coil Siphon (Pigtail) – Spiral design for compact installations.
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U-Type Siphon – Simple loop for moderate temperatures.
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Syphon with Cooling Fins – Enhanced heat dissipation.
How It Works
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The siphon tube fills with condensate (in steam systems) or process fluid.
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This liquid column blocks direct contact between the gauge and extreme heat/pressure.
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Pressure is transmitted hydraulically through the trapped liquid, protecting the gauge.
When is a Siphon Tube NOT Needed?
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Low-temperature systems (<80°C / 176°F).
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Non-pulsating, clean fluids (e.g., compressed air, water at ambient temp).
Key Takeaway
A siphon tube is a small but crucial safety device that prevents gauge failure in harsh conditions. It ensures accurate pressure readings while protecting equipment from thermal, mechanical, and chemical damage.
