- Diagnosing PT6 Borescope Articulation problems
- JT8D engine Flexible Borescope Kit Problems
- Videoscope Maintenance and Repair
- Borescopes Tip for Garrett 731.s Engine Inspections
- PT6 Guidetubes Maintenance Tip with Flexible Articulating Borescopes
- CF34 Bleed Air System
Flexible fiber optic articulating borescopes have certain common, characteristic problems when used in conjunction with rigid guide tubes.
The most common problem is a loss of travel in the distal tip or articulating section. While held in a straight and level position the tip may articulate 120/120 degrees in the up/down directions. However, when in use with a guide tube while accessing the “burner can” (or hot section) as little as 45/45 degree rotation may only be possible.
The reason is drag on the articulation cables.
This is caused by friction against the inner walls of the cable guides, normally elongated springs, particularly if they are fabricated from flat wire. While some lubrication can alleviate the problem it does not address the real cause.
While inserted in the guide tube (and the guide tube into the burner can thru the fuel nozzle) all the stress and drag is at the very front of the flexible probe of the borescope. This is caused by the twisting of the guide tube that is necessary to properly position the scope to perform the hot section inspection. This drag is conductive to stretched cables, frayed cables, broken or dislodged cables from their anchors.
Damage to the articulation cables can be reduced by not forcing extended movement of the articulating section while inserted in the guide tube. Stress can be measured by “feel” at the thumb when scanning. It will feel mushy and have some give. Trying for that extra few degrees of scan rather than repositioning the guide tube and scope, may result in the costly repair of a broken cable loose inside the probe, if not total destruction of the fiber optic components.
8mm diameter borescopes commonly used in articulating flexible guide tubes for inspecting #13 burner cans, are susceptible to fraying and damage to the probe helicoil body at the insertion point. This may be due to forcible entry and misalignment of the scope probe in the internal channel of the guide tube. This is a common frailty of the Olympus JT8 Kit and similar kits that require a “shove” tube to push the 8mm borescope probe thru the articulating section of the guide tube.
Of particular concern is the Olympus model because the probe must drop inside the guide tube housing to find the flexible section entry point, causing an “S” deviation of the flexible scope probe.
This damage occurs about 4 to 6 inches down the length of the probe from the housing and is the result of the helicoil body of the fiberscope “bird caging” or the coils overlapping.
The damage is eventually evident by loss of articulation, loss of light and loss of view due to damaged cables, damaged fiber optic light guides and damaged image guide fiber optics.
Newer technology has given us “workaround” solutions to this recurring problem.
The options are to use high resolution fiber bundles in smaller diameter fiber optic borescopes. This option is used in the Sirius 6mm diameter, four way articulating, flexible fiberscope and the EASY600 model 6mm diameter video scope and can easily fit through the restricted areas of the guide tubes.
Most video scope models require little maintenance that is different from what is common to flexible fiberscope and in some ways a lot less.
Handle and store carefully, don’t abuse by pushing, pulling, probing and over articulating in an unnecessary way and you will have an instrument that will give you years of satisfactory service.
Video scopes provide a degree of durability and low cost maintenance advantage over fiber optic flexible borescopes by the elimination of expensive fiber optics. Replacing delicate fiber optic imaging systems with wiring throughout the flexible probe section eliminates a significant cost factor in repair and maintenance work.
On the other hand, the cost of video chips and display panels remains a significant replacement problem as few, if any are available as “off the shelf” components. Yet the fact that they are far more durable than a fiber optics imaging system is a substantial cost savings advantage.
Some models are more problematic than others. For instance, the power actuated articulation systems have a tendency to fool the operator. Without a manual “feel” for the stress on the articulation cables it is easy to stretch, fray and break the cables. Sometimes the actuators will fry from the stress of over articulating, jamming against walls or too tight a fit in cavities and chambers.
Common sense approaches for prolonging the life of your
- Do not overreach! Don’t try for that extra degree of articulation if there is doubt as to how much room you have. Reposition the probe if necessary, it will save you time and money in the long run.
- Do not operate articulation unless the probe is as fully extended as possible.
- Store carefully in case. A large number of crushed or damaged probes result from improperly storing the probe in its case. Watch what you are doing, especially when closing the lid to the case.
- When cleaning you can use a “Windex” type cleaning solution. USE SPARINGLY and DRY THOROUGHLY. To dry you can use a soft cloth, cotton balls or Qtips.
Following these simple pointers can extend the life of your system significantly and reduce your maintenance costs during the lifetime of your system.
The inspection requirements of the Garrett 731 engine are very demanding for a 5mm diameter borescope because of the resolution drop-off in the fiber optic image guide or bundle.
The best size borescope to use is the 6mm diameter that contains about 10,000 pixels. This size provides the resolution necessary to avoid overextending the borescope articulation to reach closer to the base of the turbine wheel.
Trying to do the fuel nozzle section inspection with the 5mm diameter scope will result in a poor inspection. The larger scope with better resolution is needed, but too large a diameter has caused many stuck scopes requiring complete overhauls.
It is better to use a 4mm diameter as a second scope for the latter inspection.
It may seem expensive at first to stock two different size borescopes but the cost of frequent overhauls of the one 5mm diameter scope is more expensive than the cost of two scopes over the long run.
The PT6 rigid guide tubes for flexible articulating borescopes have a tendency to snag the articulating section of flexible borescopes unless the insertion end is kept free of dents that can “catch” the articulating section and/or the base ring of the borescope when being retracted.
A simple occasional reaming out of the insertion end with a flare tool will extend borescope life. You can also file off the sharp edges with a slight convex finish that will not impede insertion.
Using an 8mm video scope manufactured and sold by Borescopes R Us, Inc. simplifies the internal inspection of the bleed air tubes used for heating the leading edge cowling of the CF34 turbine engine.
Insertion access at easily accessible locations simplifies the inspection, allowing video scope recording of the inspection throughout its process. This capability reveals needed corrective actions while eliminating the complete disassembly of the front engine components and removal of the tubes and sections of the system.