The ornamental design for flow detector, as shown and described.
1. Flow detector
1.1: Front
1.2: Back
1.3: Left
1.4: Right
1.5: Top
1.6: Bottom
1.7: Perspective
1.8: Perspective
1.9: Perspective
1:10 Referential cross-sectional view
The parts shown by means of broken lines in the reproduction are not part of the claimed design; the article of the design is a flow detector which detects flow of lubricant such as grease or oil in a lubrication system installed in industrial machines such as injection molding machines or working machines; a lubricant flow channel is formed in the article, and it detects lubricant flow by electrically detecting a movement of a valve provided in the channel; 1.10 shows a referential cross-sectional view sectioned vertically at the center of the front view 1.1.
The broken line showing is included for the purpose of illustrating portions of the “article” and forms no part of the claimed design.