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If you have ever been confused about the term negative pressure, you are not alone. One reason the concept is so confusing is that negative pressure is not really negative at all. It is actually positive pressure, but it is negative in relation to atmospheric pressure. Let me explain. Early in my career (while working for an Ashcroft distributor) I had a difficult time with the term ‘negative pressure’. The only thing that I knew about pressure was filling up a balloon, a ball or a tire. How could pressure be negative? It didn’t make sense! I asked anyone and everyone to explain but never received a satisfactory answer. Today, as a Territory Sales Manager for Ashcroft, a recognized leader in pressure and temperature instrumentation - and 16 years of experience under my belt - I now have a clear understanding of negative pressure, and I am in a position to share my insight. In this article, you will not only learn how to answer the question, "What is Negative Pressure?", you will also understand how it relates to other types of pressure. At the end of the article, you will also see links to additional resources that may be beneficial to you.

This article was originally published on January 31, 2022 by John Varkonda and was updated on May 8, 2024, by Todd Thomas. Keeping pressure measurement instruments from becoming damaged in harsh environments is a challenge in many industries, including water/wastewater. Diaphragm seals play a vital role in these applications by creating a leak-tight and corrosion-resistant barrier between a pressure instrument and your process. For many, a flanged diaphragm seal connection is a great choice because it provides a convenient way to attach instrumentation directly onto flanged process piping without having to use threaded connections. But proper installation of these seals is the key to getting the most protection. Ashcroft is a recognized global leader in pressure and temperature instrumentation and uses our decades of experience to educate and guide customers to the solutions that best meet the challenge at hand. In this article, you will learn a bit about flanged diaphragm seals, the basic principles of torque and best practices for installing a flanged diaphragm seal in your process. When you are done reading, we will also share additional resources that may be beneficial to you.