What is Hysteresis and Why Does it Matter?

Sunday, October 1, 2017

At Senninger we talk a lot about hysteresis and our pressure regulators. Senninger pressure regulators have very low hysteresis, but sometimes it’s not clear why this is a benefit to irrigators. Which brings up the question, “What exactly is hysteresis?”. 

What Happens During Hysteresis?

When a pressure regulator has very low hysteresis, this means the pressure regulator is able to maintain a very similar performance while the system pressure increases versus when it decreases.

Let’s say we have an irrigation system that has just been turned on. This system has a 15 psi (1.03 bar) pressure regulator installed below a sprinkler.

As the system starts up and pressure builds, the inlet pressure will be below the regulator’s set pressure of 15 psi (1.03 bar). When the inlet pressure is below the set pressure, the pressure regulator does not regulate.

When the inlet pressure is 5 psi (0.35 bar) above the set pressure, the pressure regulator will function as designed and reduce the outlet pressure to the desired set point, which in this example is 15 psi (1.03 bar). It will maintain the outlet pressure at a constant 15 psi (1.03 bar) even if there is a variation in the inlet pressure.

As the inlet pressure of the system decreases below 15 psi (1.03 bar), the regulator will be able to maintain a similar behavior, but due to internal friction losses, the outlet pressure will be below the set point.  

This difference in the regulator performance while the inlet pressure is increasing versus decreasing is called hysteresis.

Some brands of pressure regulators are not as accurate as Senninger’s. When we talk about low hysteresis, we mean that the pressure difference when the inlet pressure is increasing or decreasing is minimal. 

Going in-depth into pressure regulator fundamentals

Learn the fundamentals of pressure regulation with Senninger's free on-demand Pressure Regulation course on Hunter University. Learn how to install pressure regulators in different irrigation systems, select a model, identify wear issues, causes of pressure fluctuations and more.

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