A partnership between Hallite Seals Americas Inc., Wixom, Mich., and The Milwaukee School of Engineering’s Fluid Power Institute (MSOE) has resulted in the development of a new test procedure for assessing the amount of dirt and dust that enters a typical hydraulic system through the rod wiper.
According to Hallite, the test for rod wipers sets a new industry standard for contaminant exclusion. The test uses a novel approach for measuring dry particles that are a major cause of hydraulic system inefficiency, degradation and failure. It fills a critical need within the cylinder manufacturing industry by helping to increase cylinder life.
In the past, said Chuck White, business development director for Hallite, wiper seals have been somewhat overlooked in the American industry. “The push now is to take what we’ve learned with our sister companies in Europe, and promote as to why a wiper is important. And why cylinder manufacturers should put more thought into these sorts of things,” White said. “The wiper of yesterday that was an afterthought is not where we’re at. It’s part of the sealing system, and we want to make that more prevalent.”
Ryan Webster, director of engineering for Hallite, said that the best way to increase cylinder, pump and valve life is to prevent contaminants from being injected into the system. “When we talk with customers, one of the single-biggest sources of contamination is, of course, down the rod seal,” Webster said.
Most hydraulic systems employ numerous cylinders that function like a syringe, drawing in contaminants. The rod wiper located in the sealing configuration of a hydraulic cylinder is designed to limit the ingression of dirt, dust and grit, making it one of the most critical system components. However, there is no specific ISO method for testing a rod wiper’s ability to prevent >4, >6 and >14 µm particles from entering the hydraulic system. These microscopic particle sizes are most damaging to hydraulic systems as referenced in ISO 4406 for coding contamination levels in hydraulic fluids.
“Valves and pumps and motors in today’s hydraulic systems are highly technical, and very, very sensitive to contamination,” added White. “If you get a little bit of contamination, it can cause total system failure, or loss of control.”
Better than the traditional test
Traditionally, gravimetric measurement was used to determine how many particle counts were in a system. But this method was nowhere near as accurate as the new system, said White.
“The MSOE rod wiper test uses an online particle counting method instead of traditional gravimetric measurement where particles are weighed,” said White. “The particle count approach provides a more complete and accurate assessment of contaminants than weight because two samples can have the same gravimetric weight in oil, but one may contain many more dirt particles than the other indicating much greater potential for damage to precision components. This new method raises the bar on keeping solid contaminants out of the system now to avoid problems later.”
In gravimetric weight measurements, an oil sample is taken before and after the test, and the weight of the oil helps determine how much particulate has gotten past the wiper into the fluid, said White. This doesn’t take into consideration what type or size of contamination the system is seeing.
Webster added that not all contamination is necessarily going to hurt the system downstream, so gravimetic measurement could sometimes spur you to replace components sooner than necessary.
How it works
MSOE used the SAE J1195 standard combined with best practices to establish a baseline for developing the rod wiper test procedure. A rig was built in the MSOE test lab and parameters such as duration, cycle rate, pressure and temperature were set using input from hydraulic cylinder manufacturers to best simulate the rigor of actual field conditions. It took eight months of development, verification, trials and adjustments to establish a repeatable test procedure. Once the new procedure was completed and proven, MSOE tested the Hallite 520 and 820 wipers against two competitors.
The test procedure involved installing the rod wiper into the specified test fixture, heating the hydraulic circulation fluid to 150˚F, pumping the oil over the top of the rod and letting it drain down into the reservoir while circulating high-velocity particles (ISO 12103-1-A4 Course Test Dust) of contamination in the chamber. The objective was to count how much dirt and grit got past the wiper. An animation of how the test works is below. In this animation, the oil is heated (1). Oil is pumped and fed beneath the rod wiper (2). Oil drains back to the reservoir (3). Dust moves at a high velocity inside the chamber as air is forced in (4). The rod wiper cleans the rod (5). The particle counter detects dust particles (6).
Based on the conditions and method used, data suggests that the Hallite 520 and 820 wipers allowed less than one half the amount of contaminant from entering into the test system compared to competitive wipers that were tested.
“Hallite has a reputation as a trusted brand for wiper technology, but we needed competitive third-party validation for the integrity of our material and design,” says White. “We are very excited about the performance results because they demonstrate how our products work in some of the most aggressive field environments. Also, working together with MSOE and key customers to develop and conduct a test of this quality is invaluable as it forged a three-way partnership that emphasizes the importance of rod wipers and gives Hallite an opportunity to demonstrate our continued commitment to understanding and developing technologies to improve the effectiveness of hydraulics systems.”
Although developed by Hallite and MSOE, the test could be used on other rod wiper seals. It gives the industry a baseline, repeatable rod wiper test. “By establishing a baseline and understanding how we measure to competitors, and how competitors measure to us, it gives us the ability to improve. And even if we are better than our competitors, we can even do better, if we see the option in design,” White said.
White said that Hallite is continuing to work with MSOE on more research partnerships to ensure reliable third-party testing.
“By cooperating with one of the leading academic fluid power research laboratories in the nation where students are building and managing the mechanical functions for test fixtures, Hallite is providing real-world interaction to help the next generation of hydraulics engineers learn more about seals and how they interact,” White said. “This paves the path for innovative future testing methods.”
And both Webster and White said that because MSOE is one of the few dedicated fluid power schools in the United States, Hallite benefits from the students and experts there.
“They’re educating us, and we’re educating them,” White concluded. “It’s just building up the fluid power industry in terms of connecting the dots because you can’t make a fluid power system work without a seal.”
Hallite Seals Americas Inc.
MSOE Fluid Power Institute