Vacuum service presents special challenges for those who must specify valves for processes that require pressures less than the standard atmospheric pressure of 14.696 psi absolute. Creating and controlling a vacuum for your process will require valves with specialized design features to cope with the low absolute pressures that will be encountered, and special sizing considerations must be made to insure that the valve will have enough capacity to meet the flow demands of a vacuum system. Creating and regulating a process vacuum requires valves of special construction, particularly where self-operated regulators are to be used. Standard pressure regulators have a range spring that pushes down on the diaphragm to act as a force balance to the pressure being regulated, whether it is downstream pressure as with the common pressure regulating valve (PRV) or upstream as with a back pressure regulating valve (BPRV).