What every technician should know about turbine fuel contamination Fuel contamination in jet fuel can lead to many problems. Most of the time, contamination is easy to control by changing filters and adhering to maintenance procedures which stress cleanliness. Unfortunately, most maintenance personnel aren't aware of the fact that fuel systems can be contaminated by microorganisms, and this contamination is difficult to control. It cannot be seen by the naked eye, and once it contaminates the aircraft's fuel system it will continue to exist unless it's controlled. The following Q & A, offered by Harnmonds Fuel Additives Inc., describes the effects of microorganism fuel system contamination in jet fuel and discusses methods for detecting and controlling it: Q. What are microorganhw or bugs? A microbe detection kit can help make a definite appraisal A. The scientific names for the types of organisms of whether or not fuel is contaminated. Above are two that live in petroleum produds are Cladosporium resinae detection kits currently available. and Pseudomonas aeruginosa. The organisms are either air- or waterborne and contaminate fuel systems by Q. Why do I need to control microbes in entering through vents, standing water in sump bottoms, fuel syatema? dissolved "free water," or trash incurred during trans- A. A sterile fuel system is one with lower mainte port or delivery. They grow at incredible rates with nance costs. That translates to reduced equipment some varieties having the ability to double in size every disruptions or downtime due to fuel system complica- 20 minutes. tions. The elimination of bugs in both storage and Q. What do these micmorganhnm do? equipment tanks will also reduce the chances of fuel A. These shybugs live and multiply in the fueY tank damage due to corrosion from the microorganisms' water interface. They actually exist in the water and acid waste products. feed off the hydrocarbons in the fuel. They are referred Q. Isn't good fuel management and 'proper to as "hydrocarbon utilizing microorganisms." As they housekeeping" enough to avoid problems? grow, they form mats that are dark in color and appear A. The highest standards of housekeeping will not gel-like. Their waste produces water, sludge, acids, and ensure the absence of microbial infestations and associ- other harmful byproducts. Microorganisms will also ated problems. Microbial spores can exist in a dormant consume rubber gaskets, O-rings, hoses, or tank linings stage for extended periods of time waiting for trace and coatings. amounts of water or improved growing conditions. Q. How do I know I have micloorganism Q. What should I do if I kdI have a problem? contamination? A. An additive is recommended (such as Hamrnonds A. The signs of microbial growth can vary. Some BiobormJF) to exterminate the infestation. The remains of the obvious signs are clogged fiiters, loss of engine might appear as coffee grounds in the bottom of the power due to fuel starvation, plugged lines, contamina- fuel tank. tion on tank bottoms, fuel with a sulphur smell and tank access lids with green or brown slimy formations. For more information on microorganism detection, A more defite appraisal may be made with the use of contact the following: a microbe detector kit. HRmmondn Fuel Additives Inc. P.O. Box 38114-407 Houston, TX 77238 Aviation Laboratories 5401 Mitcheldale #B6 Houston. TX 77092 The Best of Aircraft Maintenance Technology Magazine 29 The importance of cleanliness in hydraulic maintenance A little attention to a clean work environment can mean the difference between failure and success By Greg Napert ydraulic systems require relatively little mainte- nance on today's aircraft. For the most part, H hydraulic fluids are capable of withstandmg a wide range of operating temperatures, and the loads placed upon the systems are relatively light. So it's not in operation that these systems usually break down; instead, it's more often than not that foreign substances are unwittingly introduced during scheduled maintenance. And it's the introduction of these contaminants that work on the system and degrade it. "Ninety-nine percent of the key to hydraulic mainte- nance is cleanliness," says Paul Finefrock, president of Thunderbird Accessories Inc., in Bethany, OK. "When you work on a hydraulic component, line, or whatever, you've got to treat the area like a surgical operating room. "Cap all ends immediately, clean all your tools, and the surrounding area, and do your work in a clean environment. "And don't leave hydraulic fluid uncovered in an open container. Every bit of dust in the air will stick to the surface of the fluid, and the surface will begin to oxidize." Cleanliness is absolutely essential in a hydraulic pump due Joe Lundquist of Pall Corp., a manufacturer of to very tight clearances of the pump mechanism. hydraulic filtration systems, agrees. "We've conducted tests and have found that with hyperfine filtration and you don't stress it by shearing it or subjecting it to (below 1 micron) bearings just don't wear out. This ties high temperatures, the fluid will not oxidize and wdl in the need for better filtration. And it's more important remain stabile." especially with engines that they are trying to get more Lundquist says Pall likes to recommend that mainte and more horsepower out of. We also find that better name facilities beginning a program like this use a com- filtration can extend the life of the oil itself, the change pany that does spectrometric oil analysis. He suggests intervals. We have been doing some work in this area monitoring the oil closely until they are comfortable with on helicopters and have found our programs to be how long they should use hydraulic fluid and how often very successful. they should filter it. "If we can improve the cleanliness of the hydraulic Finefrock says that hydraulic components have system, you're looking at such things as improved become outrageously expensive; you're talking between component life and a savings on hydraulic fluid where $14,000 and $15,000 for a new Skydrolmtype pump. instead of having to change it occasionally, you can get The criticality of proper cleanliness and proper indefinite life out of the fluid. clearances in a pump are exemplified by the fad that "We're finding also that if you properly maintain a if you install gears in a pump that produce a clearance fluid by removing water (with vacuum distillation of over one and onehalf thousandths, the pump won't purification units), filtering particulate contamination, pump fluid. 30 The Best of Aircraft Maintenance Technology Magazine In fact, the mule is a good way to 'lter the hydraulic system occasionally if it has a good filter on it. We've also seen some of the rubber hoses in hydrau- lic systems break down after a period of time and begin contaminating the system. Solid lines aren't a problem. But rubber/synthetic hoses become brittle after a while and small chunks of the liner break off and contaminate the system. That's why it's important to change the hoses out at the slightest sign of them becoming brittle or damaged. There are too many aircraft flying around with 20-year-old rubber hoses that have never been changed. Inadequate filtration systems Finefrock says that, "one of the major problems with aircraft hydraulic systems is that there is no real good filter or fiation system on them. Basically, one reservoir services the entire aircraft. And the only filter Serrations in the surface of the pump body indicate on the system is a strainer that is on the inlet side of excessive contamination of the hydraulic fluid in this pump. the pump This is a fairly coarse mesh strainer, and I swear to God that coffee grounds will go through. All it Source of contarninatlon will take out is some large particle, like two microns. Finefrock says that you need to be aware of contami- "A really good idea for protecting your hydraulic nation from sources like rubber gaskets and seals. A system is to install a suction side filter on the aircraft that can filter particles down to 1 micron. a matter piece of rubber, although the reservoir strainer will take As of fact, I've installed one on mine. All you need to do is it out most of the time, can take out the hydraulic pump install a filter housing that's equipped with a bypass, and very quickly. &cause there's only between .001 to .002 a flow gauge to monitor the condition of the fdter (you'll clearance in the pump, a piece of rubber can jam need this so that you don't cause cavitation of the between the gears and seize the pump, which will shear pump), and a filter, and you'll protect the pump from the shaft. We've also seen where rubber works its way ever receiving any kind of contamination. We highly between the flat face of the gear and the housing and recommend putting this on the suction side of the pump builds until it pushes the opposite side against the hous- ing and causes metal to metal contact. And this results between the reservoir and the pump. You could put it in the gear seizing. on the return side before the fluid returns to the tank, Most contamination is primarily metal as a result of but then you wouldn't prevent contamination that's into normal wear and tear of components in the hydraulic introduced the reservoir from getting to the pump. system, however, and this slowly wears away at the Basically, you're installing the fiter to protect the pump, gears and bearings in the hydraulic pump.