Let's say we have a monopropellant, pressure-fed rocket engine. We don't want the combustion in the chamber to propagate back up the fuel line and into the fuel tank or we will have a big kaboom.
(Blow-back is always theoretically possible with monopropellants, because they burn on their own. It's not like bipropellant kerosene and oxygen; in this case, combustion can't propagate back up either one because a given propellant line has only the fuel or oxidizer, not both.)
So how is this prevented in monopropellant pressure-fed engines? Do we have to install a bunch of super-strong check valves everywhere in the fuel lines? Especially right before injection into the combustion chamber? And if so, wouldn't that imply that the engine can only fire in pulse mode (non-continuous)?
The only thing I can think of is that the pressure is so much greater than the pressure in the combustion chamber, such that the liquid (or vaporized liquid after injection) flows through the chamber so fast (speed of sound maybe, which might prevent some thermodynamic things from flowing backwards). Is this right?