Water traps and pigtail siphons are types of siphon devices used in industrial instrumentation and process control systems to protect instruments from the effects of high temperatures and pressures, as well as to prevent the entry of liquids or condensate into sensitive equipment. Here's a brief overview of each:

1. Water Trap:

   • A water trap, also known as a drip pot or liquid seal, is a simple device used to collect and remove liquid or condensate from a gas or vapor stream. It typically consists of a vertical or horizontal vessel with an inlet at the top for the gas or vapor stream and an outlet at the bottom for draining off the collected liquid.
   • As the gas or vapor flows into the water trap, any liquid or condensate present in the stream will collect at the bottom of the vessel due to gravity. The collected liquid is then drained off periodically through the outlet, preventing it from entering downstream equipment.
   • Water traps are commonly used in steam systems, gas lines, and pneumatic systems to protect instruments such as pressure gauges, transmitters, and control valves from damage due to liquid ingress.

2. Pigtail Siphon:

   • A pigtail siphon, also known simply as a siphon or coil siphon, is a U-shaped tube or coil of tubing installed between a process line and a pressure instrument, such as a pressure gauge or transmitter. It is typically made of metal tubing and filled with a liquid, such as water or a glycol solution.
   • The pigtail siphon operates based on the principle of hydrostatic pressure. When the process fluid pressure increases, it exerts a force on the liquid-filled siphon tubing, causing it to rise on one side of the U-shaped loop and fall on the other side. This creates a barrier of liquid that prevents the direct transmission of high-pressure fluid to the instrument.
   • The liquid-filled siphon also acts as a thermal barrier, dissipating heat from the process fluid and protecting the instrument from high temperatures.
   • Pigtail siphons are commonly used in steam systems, hot water systems, and other high-pressure applications to protect pressure instruments from damage due to pressure surges, water hammer, and temperature extremes.

In summary, water traps and pigtail siphons are important components in industrial instrumentation and process control systems, providing essential protection for sensitive equipment against the effects of high pressures, temperatures, and liquid ingress. Their simple yet effective designs make them valuable additions to various fluid handling systems, ensuring the reliable and safe operation of instrumentation in harsh operating environments.