Effect of combination vacuum relief and air release valve on hydraulic transients during pipeline filling process

Abstract

Combination vacuum relief and air release valve is an air valve with considerably unbalanced admission and release capacity, which could suppress the column separation and rejoinder water hammer. In order to investigate the effect of combination vacuum relief and air release valve on hydraulic transients during filling process in a pipeline system, different diameter sizes and discharge coefficients of combination vacuum relief and air release valve are selected to prevent the column separation and rejoinder water hammer. The results show that both the air admission duration and air release duration are shorter and the air volume in the valve is larger with increasing in diameter sizes of combination vacuum relief and air release valve. Moreover, although the combination vacuum relief and air release valve with bigger diameter size could admit air fastly to prevent negative pressure, the air may also be released fastly which could result in secondary column rejoinder water hammer. The results also show that the air release discharge coefficient has a more obvious role in the water hammer protection than the air admission discharge coefficient. With increasing in air release discharge coefficient of combination vacuum relief and air release valve, the air release duration shortens and the column rejoinder water hammer becomes more serious. Therefore, the combination vacuum relief and air release valve with smaller diameter size and air release discharge is benefit for the water hammer protection during pipeline filling process.