A fluid flow sampling device comprises an elongate housing and a sleeve disposed in the housing having openings corresponding to an inlet and an outlet of the housing. The sleeve is movable relative to the housing to an open position and a closed position. The open position aligns the openings of the sleeve with the inlet and the outlet to allow fluid to flow into the inlet, through the sleeve, and out of the outlet. The closed position blocks the inlet and/or the outlet with a portion of the sleeve such that fluid is prevented from flowing through the sleeve. Additionally, a coalescent filter is disposed in the sleeve between the inlet and the outlet to allow some fluid to pass through the filter for sampling and to allow another portion of fluid to flow past the filter and out of the outlet to carry away coalescent material on the filter.