How do we maintain the RPM of turbo pumps in liquid rocket engines?

[RocketAstro]

How do we maintain the RPM of turbo pumps in liquid rocket engine ? and how do we control it ? and in the case of electric pump fed engine (like rocket labs's rutherford engine) is easy but how we do it for other liquid propellant engines ?

 

[Dullard]

I'm not sure if there is a 'global' answer to your question. For the RS-25 (Space Shuttle Main Engine), exhaust gas drives the pumps. The flow of exhaust gas is throttled with a valve.

 

[hutchphd]

I think the closest to a global answer is that one controls the amount of fuel (in an oxygen-rich system) or oxidizer (in a fuel-rich system) or both (in an open system) . The possibility of bad positive feedback in this dynamic makes the production of throttleable turbine fed systems nontrivial, particularly for the staged combustion motors.