Understanding pressure builders and how to use them: A Q&A with Middlesex Gases

Jan 02, 2024

Guest Blog by the Middlesex Gases Team

“How do I operate a liquid dewar pressure builder?” is one of the most frequently asked questions from gas customers. In this article, we provide a better understanding of what a pressure builder is, how it works, and how to safely and properly use it.  

What is the purpose of the pressure builder?  

Without a pressure builder, a tank’s pressure might take several hours or days to build up to the level needed for a specific application. Using the pressure builder means the tank’s pressure will reach the desired level much more quickly, typically in 10 to 20 minutes. Some of the applications for which you might use the pressure builder include supplying nitrogen to a mass spectrometer or high-pressure manifold.  

How does the pressure builder work?  

When the pressure builder valve is opened, it allows liquid nitrogen to be introduced into the tank’s evaporation coil, which wraps around the inner and outer wall of the tank. This creates heat and builds pressure in the tank.  

How do I locate the pressure builder valve?  

There are several different valves on top of a liquid dewar, each with a tag that identifies what that specific valve is used for. Depending on the manufacturer, the pressure builder valve might look slightly different. It’s critical to read the tags to make sure you identify the correct valve that you are adjusting. If you’re looking for the pressure builder valve, search for the tag labeled “PB.” 

How do I set the tank pressure?  

Some pressure builders are designed so that the end user can adjust the pressure themselves. There are several steps that you should follow to ensure you do this properly and safely.  

  1. Wear appropriate protective clothing. At a minimum, this should include a protective face shield or goggles and gloves. If possible, wear boots and a long-sleeve shirt and pants.   
  1. Review the safety data sheet (SDS) for liquid nitrogen. This will give you a good understanding of the safety precautions and the emergency response guidelines associated with this product.  
  1. Identify the pressure builder valve. There will be several valves on top of the tank, so look for the valve with the tag labeled “PB.”   
  1. Check the pressure gauge on the tank to see if it’s at the level needed for the specific process. If it’s below the pressure required, turn on the pressure builder valve. Typically, it will take 10 to 20 minutes for pressure to build to the desired level. As pressure builds, it is normal to see frosting on the valves and base of the tank.  
  1. The pressure builder may need to be left on throughout the entire run of the equipment if the process requires a high flow rate. However, you must check the tank regularly to ensure it is maintaining the desired pressure level.  
  1. After the equipment completes a run, the pressure builder can be turned off. If you forget to do this, the liquid dewar will continue to freeze up around the valves on the tank as well as around the base of the tank. Typically, you will also hear the safeties blowing off aggressively.  

If I hear a loud hissing or popping noise coming from the safeties, is there an issue?  

This noise is normal and occurs when the tank’s pressure has built up to the maximum pressure setting. If this noise is bothersome, you may want to consider getting a whisper valve. This device can reduce the hissing noise as well as limit the amount of product lost from the safeties on the tank.  

What do I do if I find any leaks?  

Do not under any circumstances attempt to block or remove any of the safety devices on the tank to stop the leak. Immediately set the cylinder aside, mark the defective item with tape or a note, and call customer service at your gas distributor. 

Have additional questions or need more help with your liquid dewar pressure builder? The Middlesex team is happy to be of service, so feel free to contact us.  

Middlesex Gases is a preferred partner through MassBioEdge.


About Middlesex Gases 

Middlesex Gases is a family-owned, third-generation supplier of specialty, medical, and industrial gases and a variety of gas systems, including Bulk, MicroBulk, and Cryopreservation. The company was founded in 1949 by welder Joseph Martin Sr. as Middlesex Welding Supply, in Everett, Massachusetts. Today, Middlesex still offers expertise in industrial and welding gases and products but has evolved to focus more resources on serving the ever-increasing gas requirements of businesses in life sciences, biotech, and health care. Middlesex is now the preferred vendor for the Massachusetts Biotechnology Council (MassBio), the Massachusetts Medical Device Industry Council (MassMEDIC), and BioCT, Connecticut’s biotechnology community. With three fill plants, five supply stores, a state-of-the-art specialty gas lab and new medical CO2 lab, and a large fleet of trucks and trailers, Middlesex Gases delivers superior gas products and solutions wherever and whenever its customers need them. 

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