Selecting a Pressure Gauge for Anhydrous Ammonia Applications

Ashcroft has written other articles on selecting the best pressure gauges or pressure transducers for ammonia applications (see links at the bottom of this piece). However, we noticed we were still getting questions from people about the ammonia element itself. So, for the industry novice, this article will take a step back to address those specific questions. 

Ashcroft pressure and temperature instruments are used in virtually every type of industrial application, including ammonia, so it is our job to know how they will perform in every situation.

Here we will review a couple of ammonia applications, and what to look for when selecting the best pressure gauge for your specific needs. At the end of the article, you will find additional resources that may interest you.

What is anhydrous ammonia? 

Unlike the ammonia solution you will find in household cleaning products, which contains a high concentration of water, anhydrous ammonia (NH3) is 99% pure. This simple compound is used for commercial and industrial purposes and can be harmful and corrosive in concentrated forms. 

Anhydrous ammonia is not compatible with materials commonly used in liquid storage tanks and piping systems, like copper or copper alloys such as brass and bronze. For this reason, any system using ammonia must ensure that all wetted components are made with compatible materials. This will prevent potential chemical reactions that could lead to instrument failure and the release of toxic ammonia into the environment. In addition to posing a significant safety risk to workers, it can also result in costly damage to equipment and infrastructure. 

Apart from its use in mild cleaning agents, ammonia is rarely found in consumer products. It is, however, commonly used as a cost-effective and efficient refrigerant or in commercial fertilizer applications. 

How ammonia is used in refrigerant applications.

The American Society of Heating, Refrigerant and Air-Conditioning Engineers (ASHRAE) believes ammonia is a perfect alternative to traditional chlorofluorocarbon refrigerant compounds because of its low impact on the environment. On the other hand, as stated earlier, high concentrations of ammonia can be hazardous to people and animals.

How it works

As a refrigerant in commercial refrigeration systems, the ammonia circulates through heat-exchanging coils to facilitate heat transfer from the interior of refrigerators or freezers. It absorbs heat and transforms from a liquid to a gas state. While in its gaseous state, the ammonia is directed through a condenser, where fans cool it down and assist in converting the gas back into a liquid state.

Anhydrous ammonia is particularly effective for these applications due to its low boiling point of -28.01 °F (-33.34 °C), which enhances its efficiency. Accurate temperature readings are essential in determining the correct refrigerant charge, ensuring the optimal amount of refrigerant is present within the system for efficient operation.

Although this might imply a requirement for a separate temperature measurement device, the thermodynamic characteristics of ammonia, combined with the principles of the Ideal Gas Law, create a clear relationship between its pressure and temperature, eliminating the need for additional temperature instrumentation.

Figure 1. Refrigerant piping example. 

What you need in an anhydrous ammonia refrigerant pressure gauge.

For applications involving anhydrous ammonia, it is essential to use 316 stainless steel as the wetted material to prevent corrosion-related failures. Copper or copper alloys like brass or bronze should never be used in these instances.

If needed, opt for an ammonia dial option, which features both pressure and temperature scales for easy monitoring of both measurements at a glance. Additionally, the dial will be marked with the label "Ammonia."

Figure 2. Ashcroft® ammonia dial example.

When it comes to pressure gauges, compound gauges are often necessary as systems need to be thoroughly evacuated to eliminate moisture before introducing the refrigerant. Most gauges designed for anhydrous ammonia refrigerants cover ranges from 30 inches of mercury vacuum to 150 psi or 30 inches of mercury vacuum to 300 psi.

Essential factors to consider in an ammonia process for refrigerant applications.

• Ensuring compatibility of wetted parts
• Identifying the Ammonia dial
• Displaying the temperature and pressure relationship on the dial
• Incorporating vacuum and positive pressure scales

How ammonia is used in fertilizer applications.

Ammonia is an ideal fertilizer because it delivers a high concentration of nitrogen to promote plant growth. Traditionally, nitrogen was delivered to the soil in the form of solid particulate ammonium nitrate. While this chemical served its purpose, it also created potential environmental hazards due to nitrogen and phosphorus runoff that could contaminate rivers and lakes and cause toxic algae blooms.

To prevent these ill effects, a delivery system using hollow blades or spikes has been developed to inject pressurized liquid anhydrous ammonia 10 to 20 centimeters beneath the surface of the soil. Upon release, the liquid immediately vaporizes, permeating the surrounding soil and reacting with ground moisture keeping it from evaporating back into the atmosphere.

What you need in an anhydrous ammonia fertilizer pressure gauge

Similar to refrigerant applications, you will want to use 316 stainless steel wetted material to prevent the instrument from damage due to corrosion.

Unlike refrigerant applications, there is no specific dial associated with fertilizer applications. However, customers often imprint their company logo on the dial and sometimes include an additional “Ammonia” designation. If required, specify the custom dial option and provide specifications and logo artwork.

As for pressure ranges, the majority of the gauges produced for anhydrous ammonia fertilization systems are ranged as:

• 0-60 psi
• 0-100 psi
• 0-150 psi
• 0-160 psi
• 0-400 psi

Essential factors to consider in an ammonia process for fertilizer applications:

• Ensuring compatibility of wetted parts
• Identifying the ammonia dial

Ashcroft provides a diverse range of gauge models equipped with 316 stainless steel wetted parts and the ammonia dial option, such as the Ashcroft® 1009, 8008S and 8009S Pressure Gauges. Feel free to use our online gauge selector tool or reach out to us for personalized assistance in selecting the perfect gauge for your specific needs.

Go beyond the basics.

Now that you know a little more about anhydrous ammonia and considerations for selecting pressure gauges for refrigerant and fertilizing applications, here are a few related articles for your reference:

• What is a Pressure Gauge?
• The Best Pressure Gauges for Ammonia Plant Applications
• 4 Factors to Consider When Selecting a Pressure Transducer for Ammonia Refrigerant Applications
• What are the Advantages of Ashcroft Pressure Gauges?

Feel free to reach out to our product specialists here at Ashcroft to answer all of your pressure and temperature measurement questions. In the meantime, feel free to download our guide.