Experimental study of the flow in the gap of needle valve

Needle valves widely used for flow control in industry may be blocked often when they are used for a long time. The quantitative relations were deduced to relate the discharge reduction to the particle size and concentration. The gap in a needle valve is less than 100 μm, which makes it difficult to observe the flow in the gap. The particle movement in the narrow slit was analyzed theoretically and visualized through an optical glass model with a 50 μm wide gap. The results show that the particles in the oil were the main reason for the discharge reduction. Experimental results were used to relate the discharge reduction to the particle size. A suitable microporous filter membrane was then selected to eliminate the discharge reduction in a new high precision lubricator.