MHPS gas turbine M701F4 without jacking oil

Hello all,

I am new in MHPS gas turbine. Working in a CCPP. I want to know why in this gas turbine does not have jacking/ lifting oil. Even DC lube oil pump pressure is enough for turning the shaft. How is it possible? what is the mechanism. Previously I was working on GE 9FA GT. in that turbine we had jacking oil pump.

Please share your knowledge.

Thank you
Hi Niasz4,

I suggest you to make a research on the forum browser , there are some threads about GT OEM and jacking oil pump. That can be a good start for getting answer to these questions .

Also have a look on the world wide web see. I have seen some interesting threads on the subject.

Hi Niasz4,

I suggest you to make a research on the forum browser , there are some threads about GT OEM and jacking oil pump.

That's can be a good start for getting answer to these questions .

Also have a look on the world wide web see , I have see some interesting threads on the subject.

Remember if you look at pressure volume curves for a non positive displacement pump the head will be in meter WG (water gauge), if you now measure pressure with a presure gauge when you are pumping oil it will be LESS than that you which you would calculate using the wg head on the pumps curve - SG of oil will probably in in the region of 0,8 thus you would need to divide the pressure on the gauge by this figure .
okaaaayyy.... That was informative.

One MUST remember: Not all gas turbines are created (designed) equally. Not even those of the same designer/manufacturer (GE, for example, does NOT use lift oil (jacking oil) on MANY of their non F-class heavy duty gas turbines).

The desicion to use or not to use lift oil really comes down to two things: Cost and reliability. The cost issue has many factors, including the design and type of of bearings, the choice of oil pump, the speed of rotation while on turning gear (cooldown), the weight of the shafts involved and the distance between bearings, and so forth and so on. The reliability issue comes down to what risk is the designer/manufacturer willing to accept if oil pressure/flow at low shaft speeds is insufficient to prevent bearing damage if lift oil (jacking oil) is not used (which requires a separate pump and piping system and controls and logic (programming) and protection).

As you can see, there are many factors (the above, and more in some cases) about when lift oil (jacking oil) is to be used or not. It's not just the power output of the gas turbine (and generator), or the number of bearings, or the diamater of the shaft, or the number of combustors (all of which I have heard or been told--and none of which are 100% correct). There are many things which have to be taken into consideration when deciding lift oil (jacking oil) is required or not. Now, some of the early decisions when designing a new gas turbine or line of gas turbines can make the choice very simple (such as the area of the bearing surface supporting the shaft at low speed, or the type of bearing (journal versus tilting pad, for example). But, in general many things are considered in the design phase of a new gas turbine or line of gas turbines when it comes to things like whether or not lift oil (jacking oil) is desired or required.

One of the things many people (even engineering students, power plant managers and -owners) fail to recognize about engineering is: Engineering is a series of compromises. It is based on many choices which are made early on, and many economic factors, too--including acceptable level of risk (believe it or not--it's true). It's never been truer than it is today when fossil power generation is experiencing sluggish growth and even shrinkage in some sectors. But, it's also true in heavy duty gas turbines where the number of new units being sold and delivered and installed and commissioned is relatively low (compared to the early 2000's). The drive--some would say need--to cost-reduce designs and equipment is leading to all manner of new designs and changes in designs, and while a lot of it is for the better, not all of it is.

Anyway, sure, one can make all sorts of calculations based on all manner of different types of pumps and bearing area and flow-rates--but that's all done by the turbine designers/manufacturers who may have a big job when choosing such a seemingly important, or even necessary (some would say--especially those with little experience or who make lots of assumptions without much training, experience or personal consideration and analysis).

Just because one heavy duty gas turbine manufacturer chooses to use lift oil (jacking oil) on one line of their heavy duty gas turbines does not mean any other heavy duty gas turbine manufacturer must or should choose to use lift oil (jacking oil) in their similar design/size heavy duty gas turbines. Do all pick-up trucks use the same engine, or even the same transmission, or drive train, or brakes? (Granted, pick-up trucks are mass-produced, commodity items--but gas turbines are more and more like that every day (makes them cheaper to design and manufacture--and they can be sold for less money or have a higher profit margin for the same money, and profit is the product all companies really want to "make").

Hope this helps!