College of Construction Engineering��Jilin University��Changchun 130026��China

The existing foam breaking device usually can not properly achieve the requirements of defoaming in the process of foam drilling�� The indoor test-bed of foam breaking device was established to do influence test of defoaming pressure to defoaming ability�� The relationship between defoaming pressure and defoaming rate was determined based on testing different pressures and pump revolution speeds��and FLUENT software was used to make numerical simulation and analysis to the pressure distribution inside diffusion and defoaming pipes of foam breaking device�� According to analysis results��the foaming breaking device was optimally designed by increasing the length of defoaming pipe from 15 cm to 65 cm�� The indoor test results indicate that the defoaming rate of modified foam breaking device reached to about 80 %��