On the suction stroke, the roller of the supply pump follows the camshaft inward because of the force of the plunger spring . As the plunger is moved inward, a low-pressure area is created. Atmospheric pressure then pushes fuel through the preliminary filter, past the suction valve, and into the suction chamber. At the same time, the opposite side of the plunger pushes fuel from the pressure chamber into the outlet line. The pressure in this line, varying from 14 to 28 psi (1 to 2 kg/cm2 ), depending on engine application, will close the pressure valve.