Pure and simple

Dec 12, 2019

Airline profits are at near-record levels, but keeping them that way in the face of rising competition requires a relentless focus on costs. The most successful operators have already addressed big-ticket items like aircraft choice and staffing levels, but there are still a host of smaller optimizations that add up to big savings.

One performance inhibitor is hydraulic fluid contamination, which left unchecked can lead to premature wear and even failure of expensive hydraulic system components such as hydraulic pumps, servo-valves and actuators. When system flushing is necessary per the MPD hydraulic fluid sampling program, the process is time-consuming and costly – at up to $15,000 per event.

Hydraulic systems are vulnerable to four contaminants – water, air, residual cleaning solvents and solid particles – each of which pose different risks: Particulate contamination causes premature component wear and hydraulic system malfunction or failure; water causes corrosion and accelerates the formation of acids in hydraulic fluid; air drives up fluid temperatures and can result in sluggish response of the hydraulic system; and solvents can cause corrosion and attack seals.

The above contaminants enter the hydraulic system through a variety of channels, including built-in debris and break-in wear debris from new or overhauled hydraulic systems; from the environment through worn or faulty seals, or failure to replace FOD caps; and from maintenance, contaminated hydraulic fluid top-off and component replacement.

When contaminated hydraulic fluid is identified during routine sampling programs, common responses include a partial or complete system flush. However, the former is a short-term solution that only dilutes the contaminated fluid, while the latter can take up to 18 hours. Moreover, a complete flush may not fully restore system purity if the hydraulic cart is itself contaminated from previous operations.

An optimal method for decontaminating hydraulic fluid systems as part of routine maintenance is fluid purification. Not only is this process at least four times quicker than a full flush, it also avoids the procurement and waste disposal costs associated with a flush that uses roughly 100 gallons of hydraulic fluid.

Pall purifiers decontaminate hydraulic fluid in several stages. First, a three-micron-rated filter removes particulate contamination. In some purifiers the fluid then passes through a coalescer to remove any free water. Next, it’s sent to a vacuum chamber, where the fluid’s surface area is increased to allow maximum exposure to clean, dry air. Because it’s a partial vacuum, relative humidity is low, which allows gasses, volatile solvents and free and dissolved water to be extracted from the oil and exhausted out of the vacuum chamber.

The entire process is accomplished in an acceptable time frame and fluid can be cleaned up to ‘as new’ condition or better. Vacuum dehydration technology ensures negligible fluid performance degradation compared with other purification methods such as flash distillation.

Some models of Pall purifiers connect to hydraulic power units, or mules, which then connect to the aircraft hydraulic system. Airlines can also connect Pall’s HSPA purifiers directly to aircraft, since the purifier can operate at aircraft hydraulic system pressure (3000 psi). Best results are attained by using the system during a heavy check, and Pall estimates the system will pay for itself after just eight uses, or less than a year for many airline fleets.

Fluid purifiers are used in most branches of the US military. In one case an F-16 base reported that faulty filters were behind most of its ground aborts. In fact, Pall found their filters were clogged and in bypass mode. After connecting a NATO-codified Pall purifier to its hydraulic mules, the hydraulic fluid became 1,000 times cleaner, and after 2,000 flight hours the base had suffered no additional filter-related aborts. Furthermore, hydraulic system labor costs had halved, while hydraulic discrepancies were down 38%.   

Commercial airlines are now also exploring the technology, while maintenance providers and OEMs are using purifiers for their production and testing equipment.

Compared with traditional hydraulic fluid decontamination methods, the benefits of using a fluid purifier include better reliability, quicker maintenance, and lower costs.