Figure 992 - Combination Vacuum Breaking and Air Release Valve - Datasheet

COMBINATION AIR VALVESPage 59 A Product of GA IndustriesCOMBINATION VACUUM RELIEF& AIR RELEASE VALVESizes 2-1/2” through 12” Flanged Inlet - For Clean Fluids Only FIG. 992COMBINATION APPLICATION DATAFIG. 992 FOR PARTS LIST SEE PGS. 9 & 32SIZES 2-1/2” - 12”GENERAL DIMENSIONSSIZE 2-1/2” 3” 4” 6” 8” 10” 12”A 18” 18” 20” 22” 24” 28” 30”B 14-3/4” 15” 15-3/4” 17” 18-1/2” 23-1/4” 23”C 8” 8” 10” 12” 14” 18” 20”WGT. 62 68 86 115 175 245 380(LBS.)ENGINEERING SPECIFICATIONThe Combination Vacuum Breaking and Air Release Valve shall open toadmit large amounts of air when the pressure in the pipeline or vessel fallsbelow atmospheric, reclose upon restoration of positive pressure and releasesmall amounts of accumulated air while pressurized. The Combination Valveshall consist of two independent valves; a Vacuum Breaking Valve and an AirRelease Valve, piped together and tested as a unit. Rapid entry of air into thevalve shall be accomplished by having 10% more inflow area than the equiva-lent size of the valve.The Vacuum Relief Valve shall be normally closed and open only when the pressure in the pipeline or vessel falls to approximately 1/4 psi below atmos-pheric pressure. The body of the valve shall be constructed of cast iron con-forming to ASTM A126, Class B. The disc and seat ring shall be made ofbronze conforming to ASTM B62. Tight shut-off shall be provided by a metalseat with a resilient seal. Internal spring shall be stainless steel. The air inletshall be protected by a stainless steel screen and steel hood to prevent theentry of foreign materials.The Air Release Valve shall be of adequate size to release small amounts of accumulated air at up to the maximum working pressure of the system. It shallhave a cast iron body and cover conforming to ASTM A126, Class B, all stain-less steel internal trim and float and a rubber seat for tight shutoff.The Combination Vacuum Breaking and Air Release Valve shall be as manufactured by GA Industries, Inc., their Figure 992.Why Use Vacuum Relief Valves?Most often, pressure containing systems, such as pipelines,filter canisters or tanks, are designed to withstand many timesthe normal pressure without damage. However, certainpipelines and pressure vessels are easily damaged when sub-jected to an internal vacuum caused by the closed system. Inparticular, thin wall large diameter pipe and vessels are sus-ceptible to damage caused by vacuum conditions beyond theirdesign. It is extremely important that these systems be protect-ed by “relieving” the vacuum before it reached a critical point.What Do They Do?Vacuum Relief Valves automatically open and admit air intoa pipeline, vessel or system, when the internal pressure dropsto a predetermined level below atmospheric, thereby “making-up” the vacuum and limiting the vacuum pressure to within thedesign of the system.How Do They Work?Vacuum Relief Valves are installed at points where a vacu-um would first tend to form if the system would drain, either bydesign or in an emergency, such as line break or power out-age. They are normally held closed by a spring or weight anddo not open unless the internal pressure drops below atmos-pheric. When the pressure inside the pipeline or vessel dropsto a point where the external atmospheric pressure overcomesthe spring or weight, the valve opens and rapidly admits air.The valve will re-close upon restoration of pressure higher thanthe setting of the valve. Vacuum Relief Valves can be com-bined with Air Release Valves to allow residual air to escapeafter the Vacuum Relief valve has re-closed.Where Are They Used?Figure 993 Vacuum Relief Valves are used on water sys-tems where it is necessary to prevent critical vacuum forma-tion. They are sometimes used in conjunction with Air/VacuumValves to supplement the Air/Vacuum Valve's inflow. This isparticularly critical when there is a wide difference in the fillingand draining flow rates, such as on a steep pipeline gradient,or when thin-wall, large diameter steel pipe is used.What Is The Difference Between VacuumRelief Valves and Air/Vacuum Valves?Vacuum Relief Valves are NORMALLY CLOSED and areONE-WAY valves. They open only upon excessive vacuum toadmit large amounts of air into the system to prevent a criticalvacuum condition. Once internal pressure returns to the settingof the valve, it closes and air in the system cannot escapethrough it. Air that had been drawn in through the VacuumRelief Valves must be exhausted by other means.Kinetic Air/Vacuum Valves are NORMALLY OPEN and areTWO-WAY valves. They exhaust air from AND admit air into apipeline or system. The valve is always open when it is notfilled with liquid and held shut by positive pressure in the system. When system pressure drops to near atmospheric(impending vacuum) it opens and admits air. However, as liquidrefills the system, air that had been drawn in can also beexhausted through the Air/Vacuum Valve.NOTE: This valve has been effective in installations where water col-umn separations occur following a pump trip, minimizing subsequenthigh shock pressures when the columns rejoin. It freely admits air,but vents it slowly through the Air Release Valve, thereby providing acushion of air to reduce the impact of the rejoining water columns,thus lessening the surge potential of the system. However, it is notsuitable to vent air when filling pipeline.