Looking back

Pressure regulators have changed a lot since they first came on the scene.
BY DIANN ILKENHONS
Editor’s note: This article was written by Diann Ilkenhons following an interview with Mark Healy, designer of the industry’s first in-line pressure regulator in 1966. 

Like many great ideas, the concept of using pressure regulators in an irrigation system started as just a scribble on a paper napkin. Mark Healy remembers sitting with his uncle, Joe Senninger, as Joe sketched his earliest prototype. He then handed the concept to Healy, asking him if he could design it to be made of plastic. 

In the mid-1960s, Joe Senninger was at the helm of Senninger Irrigation, a company in its infancy. Its main product was a plastic insect-proof sprinkler usually mounted above the orange trees on 21-foot riser pipes. Senninger noticed system flow issues in orange groves with undulating terrain where the lower areas received too much water while the higher areas received too little. He knew about using pressure regulation from other industries and thought it would make sense to bring the concept over to irrigation.

The average design pressure of most orange grove overhead irrigation systems at that time was 50 psi. “We first machined an aluminum model to determine the validity of the design and the relative size of the internal parts needed,” Healy explained. 

“With that knowledge,” Healy added, “we made single-cavity molds for most of the parts to see if the concept would work in plastic as we hoped. With our initial success, we made only a 50-psi pressure regulator.” 

(A) The prototype of the pressure regulator. (B) The first pressure regulator mold for the lower housing was chromed for display in the Senninger museum. (C) Regulator showing the upper and lower housing held together by stainless steel screws. (D) Early no-leak snap-together regulator.

Trial & error

Back in the ’60s and early ’70s, there were not nearly as many plastics and plastic alloys as there are today. Senninger and Healy molded several prototypes out of many of the different plastics available until they found a formula with the strength and chemical resistance needed. It was a tedious process. Each material change necessitated a mold change, but that offered an opportunity for product enhancement. The first models were produced using female ¾-inch NPT connections with 50 psi outlet pressure mainly for the overhead citrus irrigation. 

Because the regulators were set above the orange trees baking in the hot Florida sun, it was evident that more changes were needed in the plastic composition and the diaphragm makeup.  

Healy recalls, “During the early ’70s, we broadened our range of models by using different springs to achieve specific outlet pressures. We changed to a white upper housing and printed the pressure rating using a hot-stamp process. Then we increased our production capacity by making multi-cavity tooling.” They also started making pressure regulators with ¾- and 1-inch NPT connections. With all the additional models and enhancements, pressure regulators became attractive to other markets.


Because the regulators were set above the orange trees baking in the hot Florida sun, it was evident that more changes were needed in the plastic composition and the diaphragm makeup.


Expanding to pivots

Pressure regulators made their way onto center pivots during the 1970s. Healy went on to say, “At that time, all models were made up of an upper and lower housing held together by stainless steel screws. Around 1980, we were challenged by a very good customer to see if we could make a pressure regulator without screws holding it together. While the current models worked perfectly fine, if we could find a way to eliminate the need for screws, the product would be much easier to manufacture, and it would be tamper-proof.” 

Healy took the challenge and began working with engineer Bill McFadden, drafting out concepts and testing designs, much like he and Joe Senninger had done many years before. Eventually, they developed a design and assembly method using a specific plastic alloy. They were able to make a no-leak snap-together regulator. 

The materials used to manufacture pressure regulators changed over the years to better resin blends that would resist chemicals like liquid fertilizers and withstand extreme temperatures like those found in expanded global markets. 

“Initially, we molded unreinforced diaphragms. However, we soon changed to a reinforced material,” Healy added. “Spring suppliers can now produce more accurate springs. Additionally, we have tightened the tolerances of both our molded and purchased parts.”  

Early hysteresis chart illustrating the difference in pressure regulator performance, while the inlet pressure is increasing versus decreasing

Years ago, to measure the accuracy, Healy used “hysteresis,” an electrical term simulating what happens inside a motor. The word caught on in the irrigation industry. Hysteresis refers to the difference in pressure regulator performance, while the inlet pressure is increasing versus decreasing. If a pressure regulator has very low hysteresis, this means it can maintain a very similar performance while the system pressure increases versus when it decreases. The lower the hysteresis, the more accurate the pressure regulator will be.

No pressure regulator is perfect, but those with the highest accuracy are better at maintaining the desired outlet pressure.

With today’s low-pressure systems, pressure regulation is critical for maximum efficiency. Most irrigation systems will experience pressure fluctuations or flow deviations that could easily produce overwatering or underwatering resulting in uniformity issues. System pressure can change due to pressure loss through pipes and fittings, end guns cycling on/off on a center pivot, or zones shutting off in a nursery or open field. 


“They [pressure regulators] more than pay for themselves by reducing water loss while helping to maintain irrigation uniformity and crop yields.” – Mark Healy  


“Pressure regulators exist to maintain a system’s desired performance,” Healy said. “They more than pay for themselves by reducing water loss while helping to maintain irrigation uniformity and crop yields.  We appreciate the irrigation dealers who promote pressure regulation and the growers that use them.  We believe their use helps save water and energy — resources on which we must all focus.” 

Diann Ilkenhons is the marketing manager for Senninger Irrigation.
Mark Healy recently celebrated his 55th anniversary with Senninger Irrigation. A prolific engineer, Healy received the Irrigation Association’s Industry Achievement Award for “outstanding contributions to the development of the irrigation industry and its products” in 1994 along with his brother, Andy Healy. In addition to designing the industry’s first in-line pressure regulator in 1966, he is responsible for developing a long list of innovative products that have revolutionized how irrigation products are designed and manufactured.
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