The flow indicator has a highly visible red nylon ball that rotates in a circular channel during flow. Continuity and relative flow rate are indicated by the speed of the ball's rotation. The minimum flow rate to actuate the ball with water is 50mL per minute in a horizontal position and 140mL per minute in a vertical position. With air, the minimum flow rate is 3 liters per minute in a horizontal position and 8 liters per minute in a vertical position. Maximum working pressure is 10 psig. (69 kN/m2). The polystyrene indicator measures 39mm x 57mm (8 3/4" x 2 1/5") with two 23mm (.09") long tube extensions to accept 6.4mm (1/4") to 9.5mm (3/8") I.D. tubing. An arrow shows direction of flow.