Abstract: A dispensing apparatus for viscous substances includes a unitary plastic block housing provided with a vertical bore forming a dispensing cylinder and a horizontal three way spool valve operable for controlling a dispensing piston located in the aforementioned dispensing cylinder. The dispensing piston is attached to a shaft extending centrally upwardly of the dispensing cylinder and is adjustable for controlling the stroke of the dispensing piston and thereby the quantity of material dispensed. A common source of air pressure is applied to the minor area on the shaft side of the dispensing piston as well as to the material to be dispensed. The material under pressure is normally applied to the major side of the dispensing piston via the spool valve. When the spool valve is operated the supply of material is cut off and the dispensing cylinder is connected to an exit port, whereby the air pressure behind the dispensing piston is sufficient to force a predetermined quantity of material through the exit port.