Generally speaking, a siphon is a small, heat dissipation device used to protect pressure instruments from high-temperature media and reduce the possible damaging effects of rapid temperature change. There are different types of siphons, each designed for specific applications, from industrial to everyday use. This article will focus on industrial applications found in power generation, oil and gas, chemical and petrochemical plants and water/wastewater management, to name a few.
As part of Ashcroft's Understanding the Basics series, this article will explore the different types of siphons used as heat dissipators in both steam and non-steam applications. Continue reading to learn which siphons are used for these purposes and how they work. You will also see links to additional information on these instruments and resources to enhance your understanding of maintaining instrument safety in challenging environments.
What type of siphons are used in steam application?
In another Ashcroft article, we explained that steam is used as a pressurized fuel source for energy production in refineries, petrochemical plants, and industrial factories. Because steam generates significantly high temperatures and pressures in your process line, you need to take steps to protect your measurement instruments from getting damaged.
Two types of siphons are specifically designed to shield gauges from high process temperatures:
1. Pigtail siphons
Pigtail siphons are specifically made for vertical piping configurations. Their unique pigtail design creates a natural trap for liquid accumulation, creating a protective barrier for your pressure instrument against high steam temperatures. The barrier allows the steam to cool and condense into liquid within the loop to ensure only cooler liquid reaches the instruments.
Figure 1. Ashcroft® 1100 Pigtail Siphon
2. Coil siphons
Coil siphons can be used for steam applications with either vertical or horizontal piping. The loop in its design features a small dip that traps water, forming a barrier against steam heat and ensuring only cooler liquid reaches the gauges. This process helps that gauge maintain accurate pressure readings and protects gauges in various industrial settings.
Figure 2. Ashcroft® 1098 Coil Siphon
How steam siphons protect your pressure gauges
Typically, pressure gauges have an operating temperature range of 200 °F (93 °C) to potentially 250 °F (121 °C), and even steam at lower temperatures can reach levels that may harm a gauge. To prevent damage, a pigtail or coil siphons are:
- Filled with water prior to installation
- installed directly on the piping before a pressure gauge
As the process heats up and the steam comes in contact with the water, which cools it down before reaching the gauge. During the process, the siphon facilitates the conversion of steam from a gas to a liquid by dissipating its heat energy, which then condenses, forming a liquid barrier within the siphon loop.
Although air might become trapped inside the siphon, it is not a concern. Since air is compressible, you will still obtain an accurate gauge reading. Your main priority is protecting your instruments from extreme temperatures, making pigtail and coil siphons great options for steam applications.
What type of siphons are used in non-steam applications?
In a separate article, Pressure Gauge Accessories for Non-Steam Applications, we reviewed several options for protecting instruments from extreme temperatures that come from the environment and your process media. The emphasis on applications that do not involve steam starts with understanding the temperature limits of your pressure instruments.
If you use a gauge for an application that goes beyond its temperature limits, you are at risk of damaging the gauge and jeopardizing the safety of your entire operation. Depending on the type of temperature (ambient, process or storage) your pressure gauge's temperature range can vary.
Figure 3. Ashcroft min/max temperature limits
When you know your pressure gauge will be used in processes that exceed its temperature limits, two types of siphons can protect your pressure measurement instruments, increase their lifespan and help ensure they maintain accurate measurements.
1. Microtube siphons
This type of siphon is compatible with many different process media and is designed to protect instruments including pressure gauges, switches and transducers.
For example, the Ashcroft® MicroTube™ Siphon is made with 316L Stainless steel construction and has a maximum allowable working pressure of 5,000 psi. It can be used between a pressure gauge and a diaphragm seal and is able to reduce temperatures from up to 800 °F (427 °C).
Figure 4: Ashcroft® MicroTube™ siphon
Figure 5: Microtube siphon heat dissipation chart
2. Finned siphons
This type of siphon has a fin design that increases the surface area that comes in contact with the surrounding environment. This enables the fluid to cool down before it reaches the pressure instrument.
One example is the Ashcroft® Finned Siphon made with 316 Stainless steel or Monel material and has a compact design with direct mount installation. It is able to reduce temperatures from up to 700 °F (371 °C) and can contain pressure up to 3,000 psi.
A built-in dampening mechanism is also featured to help control the effects of pulsation and dissipate pressure spikes and surges. Similar to the microtube siphon, the finned siphon is also compatible with different process media and is a great choice for protecting instruments including pressure gauges, switches and transducers.
Figure 6: Ashcroft® Finned Siphon
Figure 7: Finned siphon heat dissipation
Ready to learn more?
Now that you have a high-level understanding of the different types of heat-dissipating siphons and how they work, you may be interested in a few other articles that can deepen your knowledge even further.
- How Does Temperature Affect Pressure Gauge Performance?
- How Does Media Temperature Affect Pressure Transducer Performance?
- Why Did My Pressure Equipment Fail? 6 Instrument Killers
- What’s the Right Pressure Instrument Mounting Assembly for Me?
- Do Measurement Instrument Accessories Affect Accuracy?
Feel free to contact one of our industry experts with additional questions. In the meantime, check out our complete assembly guide to learn about other ways to protect your instruments. 