Complex sentence: This instrument could not have been developed without the improvement of piston valves by Heinrich Stölzel and Friedrich Blühmel In the early 19th century these two instrument makers almost simultaneously invented valves.
Split into simpler sentences: This instrument could not have been developed without the improvement of piston valves by Heinrich Stölzel and Friedrich Blühmel in the early 19th century. These two instrument makers almost simultaneously invented valves.