Valve apparatus for controlling flow of particulate material, such as sand or other abrasive material, from a tank or hopper. The valve has a unitary plunger which is movable axially with respect to a lateral particulate material inlet between positions closing and opening the inlet, the plunger being moved by rotation of a threaded portion of the plunger through an internally threaded cap or bonnet opening. The valve body passage through which the plunger is disposed, and the plunger itself, are formed to have abrasion-resistant surfaces. A lateral air pipe nipple sealed to the valve body receives the abrasive material flowing through the valve for use in sand blasting operations.