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It is easy to find data about rocket engine propellant, but quite difficult to find information about other fluids used in rocket engine. For engine using a turbopump, this pump turns at quite high speed. Such a piece of mechanic should require lubrication in order to work for more than few seconds.

My question is: in engine using turbopumps (RD-107, RS-25, Vulcain,...) how are the turbopump and other moving parts lubricated? What kind of lubricant is used and how is it distributed to moving parts?

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    $\begingroup$ The fluid pumped may be used as lubricant too. A hyrdrocarbon lubricant could not be used for a liquid oxygen pump. $\endgroup$
    – Uwe
    Apr 11, 2019 at 19:59
  • $\begingroup$ Yep, using the working fluid as the lubricant is pretty common. $\endgroup$ Apr 11, 2019 at 20:58

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The bearings in the SSME (RS-25) had/have no conventional lubrication as such. They were cooled by minute flows of their respective propellants.

Knowing that the bearings have no lubrication except from a minute transfer film of the Polytetrafluoroethylene (PTFE) from the cages to the balls, several attempts at improving the lubrication and lowering the heat generation in the bearings was investigated.

Source: History of Space Shuttle Main Engine Turbopump Bearing Testing at the Marshall Space Flight Center

Also

HPOTP bearings deteriorate quickly for many reasons. The balls wear the fastest of all the bearing components and, in the process, lose their preload. Liquid oxygen is their only lubricant and a poor one at that.

From here

(HPOTP is High Pressure Oxidizer Turbopump)

You can see the coolant passage in this cutaway drawing of the Low Pressure Fuel Turbopump from here.

enter image description here

Also see here for more on the High Pressure Fuel Turbopump and here for the High Pressure Oxidizer Turbopump.

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  • $\begingroup$ Polytetrafluoroethylene is a plastic material, not a propellant. Unless they're burning plastic as fuel? $\endgroup$
    – user253751
    Apr 12, 2019 at 0:08
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    $\begingroup$ I am not sure what point you are trying to make. The quoted document is just saying that some of the PTFE is transferred from the bearing cages to the ball bearing and that this is the only substance actually acting as a lubricant. The bearings are cooled by propellant flow, oxygen for the oxygen pumps and hydrogen for the hydrogen pumps. $\endgroup$ Apr 12, 2019 at 0:08
  • $\begingroup$ Apparently, the Block I/IA SSME design improvements included the use of hydrogen also to cool the oxygen turbo pump bearings (p. 7 in the paper). Admittedly, cooling hot metals with liquid oxygen does sound just wrong but then what do I know. Apparently hydrogen isn't really good to metals either. $\endgroup$ Jan 23, 2022 at 14:09
  • $\begingroup$ Also, the first sentence sounds a bit too absolute: Whether solid lubrication is "conventional" is in the eye of the beholder, and it did have that (the Teflon), and it was important. $\endgroup$ Jan 23, 2022 at 14:14

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