Engineers use a variety of terminology to describe vacuum, which can cause some confusion. Determine whether the units are in absolute pressure or gauge pressure (0 psi gauge (0 bar gauge) is atmospheric pressure).

Vacuum Control Devices

Just like there are pressure reducing regulators and pressure relief valves for positive pressure service, there are also two basic types of valves for vacuum service. The terms used for each are sometimes confusing. Therefore, it is sometimes necessary to ask further questions to determine the required function of the valve. Emerson Process Management Regulator Technologies uses the terms vacuum regulator and vacuum breaker to differentiate between the two types.

Vacuum Regulators

Vacuum regulators maintain a constant vacuum at the regulator inlet. A decrease in this vacuum (increase in absolute pressure) beyond setpoint registers on the diaphragm and opens the disk. It depends on the valve as to which side of the diaphragm control pressure is measured. Opening the valve plug permits a downstream vacuum of lower absolute pressure than the upstream vacuum to restore the upstream vacuum to its original setting.

Besides the typical vacuum regulator, a conventional regulator can be suitable if applied correctly. Any pressure reducing regulator (spring to open device) that has an external control line connection and an O-ring stem seal can be used as a vacuum regulator. Installation requires a control line to connect the vacuum being controlled and the spring case. The regulator spring range is now a negative pressure range and the body flow direction is the same as in conventional pressure reducing service.

Vacuum Breakers (Relief Valves)

Vacuum breakers are used in applications where an increase in vacuum must be limited. An increase in vacuum (decrease in absolute pressure) beyond a certain value causes the diaphragm to move and open the disk. This permits atmospheric pressure, positive pressure, or an upstream vacuum that has higher absolute pressure than the downstream vacuum, to enter the system and restore the controlled vacuum to its original pressure setting.

A vacuum regulator is a spring-to-close device, meaning that if there is no pressure on the valve the spring will push the valve plug into its seat. Emerson Process Management Regulator Technologies has various products to handle this application. Some valves are designed as vacuum breakers. Emerson Process Management Regulator Technologies relief valves can also be used as vacuum breakers.

A conventional relief valve can be used as a vacuum breaker, as long as it has a threaded spring case vent so a control line can be attached. If inlet pressure is atmospheric air, then the internal pressure registration from body inlet to lower casing admits atmospheric pressure to the lower casing. If inlet pressure is not atmospheric, a relief valve in which the lower casing can be vented to atmosphere when the body inlet is pressurized must be chosen. In this case, Emerson Process Management Regulator Technologies uses the terminology "blocked throat" or "external registration with O-ring stem seal."

A spring that normally has a range of 6 to 11-inches w.c. (15 to 27 mbar) positive pressure will now have a range of 6 to 11-inches w.c. (15 to 27 mbar) vacuum (negative pressure). It may be expedient to benchset the vacuum breaker if the type chosen uses a spring case closing cap. Removing the closing cap to gain access to the adjusting screw will admit air into the spring case when in vacuum service.

Vacuum Regulator Installation Examples