PT6 Fuel Nozzel Maintenance

PT6 Fuel Nozzle Maintenance By Peter Boissonneault September 1999 The Pratt & Whitney PT6 engine has proven itself to be one of most reliable and cost efficient engines ever developed. Operators, and those of us in the repair and overhaul...


PT6 Fuel Nozzle Maintenance




The Pratt & Whitney PT6 engine has proven itself to be one of most reliable and cost efficient engines ever developed. Operators, and those of us in the repair and overhaul business, have become keenly aware that the ever-reliable PT6 is not immune to increasing maintenance costs. The challenge of maintaining high levels of quality while holding the line on costs is always present. Maintenance and repair organizations, which are capable of meeting the ever-increasing quality demands of its customers, and at the same time controlling costs, will surely be in demand.

This article will address one aspect of hot section maintenance, those dealing with fuel nozzles and their proper servicing.

Design and Installation
The fuel nozzle design and installation in the PT6 engine is simple and efficient. The installation consists of 14 adapter assemblies consisting of, primary, secondary, and inlet adapters of either simplex or duplex design. Unfortunately there exists some misunderstanding regarding the ongoing maintenance, recertification, and required overhaul of the fuel nozzles. We will make every effort to clear up some of the confusion on this topic and outline some of the choices available to you.

The Pratt & Whitney maintenance manual addresses recommended and approved fuel nozzle servicing procedures. The manual outlines recommended time intervals, inspection tasks, fits and clearances, cleaning procedures, leak testing, and flow checks.

Time intervals between fuel nozzle servicing should initially follow the Pratt & Whitney maintenance manual recommendations. Once an operator gains a history or trend on the condition of their fuel nozzles, adjustments such as time extensions or contractions might be warranted.

Inspection
The initial incoming inspection for damage to the tip, adapter, and sheath should be completed first.

It's very important to carefully check each nozzle tip for the correct part number. Fuel nozzle sets with incorrect part numbers installed can not only be dangerous but cause extensive hot section damage.

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The installation of an incorrect tip on an adapter is possible since a variety of part numbers have the same physical and outward appearance. This problem is more prevalent with fleet operators using various engine models. The ultrasonic cleaning procedures for fuel nozzles are outlined in the P&W maintenance manual. The use of a smaller, dedicated ultrasonic cleaner, works best. Cleaning one set of nozzles at a time avoids the possibility of co-mingling customer or engine sets. The proper cleaning of fuel nozzles takes time and is a procedure that should not be rushed. Improper cleaning procedures often result in unnecessary nozzle tip replacements.

Repeat cleaning
The P&W maintenance manual outlines that if nozzles fail to clean up, the procedure may be repeated. The repeat cleaning is an important consideration when it comes to holding the line on fuel nozzle expenditures. In fact, the second cleaning often results in the return of a normal flow pattern. Replacement nozzle tips are expensive and should only be required when multiple efforts to clean them fail.

The next step in the process is leak testing. The leak test reveals any problem between the nozzle tip, lock tab, and adapter assembly at the sealing areas. Also important to note at this time is external leakage at welds, and areas between primary and secondary ports.

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