Please can somebody explain to me the purpose of the vent pipe on bearing number 2 of the GE Frame 9E Gas Turbine. Also what could be the cause of the tell tale line from bearing 2 leaking air to the outside of the Turbine?
The purpose of the vent pipe on bearing number 2 of the GE Frame 9E Gas Turbine is to supply pressurized sealing air from either the 11th stage or 5th stage of the compressor to the #2 bearing area. It also provides a path for piping to provide vacuum from the mist eliminator to the #2 bearing area. Lastly it provides a path to exhaust excess bearing seal air.
Most likely if you are getting high pressure high temperature compressor air coming out of the tell tale drain line outside the turbine package then the tell tale tubing or fitting has fractured inside the turbine compressor casing area. This is a fairly common issue to this type of machine. This failure can typically be identified by a borescope technician who knows where to look in the lower CDC case area. In my experience this fracture most often occurs inside the CDC case where the tubing is secured with clamps, or at the Swagelok pass through fitting inside the CDC case.
If you are familiar with the GE drawings or if you have a contract with GE, your customer performance manager can help you find the drawings that will show the routing of the tell tale tubing and its associated hardware.
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>Please can somebody explain to me the purpose of the vent
>pipe on bearing number 2 of the GE Frame 9E Gas Turbine.
The #2 bearing of a GE-design Frame 9E heavy duty gas turbine is located between the axial compressor and the turbine sections of the shaft, and as such it is internal to (inside) the unit, and it is very hot in this area (axial compressor discharge temperatures are several hundred degrees F, and first stage turbine inlet temperatures are a couple thousand degrees F).
The vent pipe allows oil vapours from the #2 bearing enclosure to be evacuated by the L.O. Mist Eliminator, and I believe there is also a path for cooling and sealing air to enter the #2 bearing area (it's not a large flow, but necessary).
>Also what could be the cause of the tell tale line from
>bearing 2 leaking air to the outside of the Turbine?
I'm not 100% certain exactly what you're talking about, but if the air is hot and under pressure (more than 1 barg, for example) then there's likely a leak somewhere that's allowing cooling and sealing air to get out into the cavity surrounding the #2 bearing. I believe, if we're talking about the same "tell tale" line (there are a couple of "drains" referred to a "tell tale" lines on some GE-design Frame 9E heavy duty gas turbines depending on vintage and fuels and other circumstances), that line (if it is from the #2 bearing area and not some other location) is to be able to tell if there is an oil leak of the bearing "seal" system. A lot of people confuse the liquid fuel purge check valve tell tale leakoff with something coming out of the #2 bearing area because it's very difficult to see down there, especially when the unit is running. The Operations & Service (Maintenance) Manuals provided with the unit should have drawings of each system (usually called Piping Arrangement drawings) to detail where each line originates, which can be very helpful in discerning what each line does. (While some OEMs put numbers on valves or piping (such as leakoffs or tell tales) to help identify the system and the function, this particular hasn't seen fit to do that for many years--except on hydrogen-cooled generator piping systems....)
Hope this helps!