Reducer
Reducer turns up in 2 fields: valves, mechanical. Here is what it means to the people in each one.
Reducer in valves
A fitting that joins a larger pipe to a smaller one, either on a common centerline or with one side flat.
Concentric reducers taper evenly, keeping both pipes on the same centerline. Eccentric reducers keep one side straight: at a pump suction they go in flat on top so no air or vapor pocket forms, and on pipe racks they often go flat on bottom so the pipe keeps its support elevation. Control valves are commonly installed between a pair of reducers because they are smaller than the line.
"Eccentric reducer at the pump suction goes flat on top, if you flip it you'll trap an air pocket and air-bind the pump."
Reducer in mechanical
A mechanical or hydraulic device that decreases input speed or pressure to increase output torque or displacement.
A transmission component or hydraulic mechanism designed to step down the input from a prime mover. In mechanical systems, a gear reducer lowers rotational speed to multiply torque. In fluid power and testing machines, a hydraulic reducer steps down pressure over a larger area to produce a larger, more controlled movement for heavy load applications.
"Check the oil level in the main reducer before we fire up the conveyor."