A line strainer for screening fluid flow in a small diameter conduit is constructed with an integral housing of clear or transparent thermoplastic polymer. A fluid flow channel through the housing center is terminated at opposite ends by sonically welded end fittings. Internally of the housing, a screen chamber is separated from a flow meter chamber by a screen support hub with flow diversion passages. The screen chamber confines a conically formed screen mesh for passing substantially all flow through the housing. The flow meter chamber has conically tapered walls that support radial fins projecting from the walls inwardly to a cylindrical void that confines the metering ball to displacement along the housing axis. A spring bearing against the metering ball resiliently biases the ball toward the flow restriction passage and against the fluid flow direction. The spring bias and conically tapered meter walls cooperate with the flow stream and metering ball to stabilize at a position along the housing axis that is proportional to the flow rate through the screen. As the screen mesh fills to increase flow stream resistance, the metering ball approaches the flow restriction passage signaling a reduced flow rate. The degree of plugging or filling of the screen mesh is therefore indicated by the relative position of the metering ball for a substantially constant pressure source. Additionally, pump performance or system blockage could also be detected by the ball position in the flow meter chamber.