It is important to calculate the burst pressure of capillary burst valve used in a microfluidc system. When the passive valve is limited by a glass flat cover with good hydrophilicity

the experimental results shows that some liquid contact line will pass through the entrance of expansion section on the case of a glass cover

but the valve still have a capability of stopping a liquid flow. The current simulations of capillary burst valve are not exact for the above condition. The Surface Evolver (SE) was successfully used to simulate the burst pressure of the microvalve composed of the glass cover and PDMS microchannels by posing the properly boundary condition and monitoring the variation of the contact angle at the entrance of expansion section. For the microvalves with 25μm depth and the aspect of 2

4

8 and 16

the capillary pressures are 0.77

0.45

0.33 and 0.24KPa

respectively. The obtained simulate data have agreement with experiment data. The effect of the contact angle is discussed and the simulations show the valve do work until the sum of the contact angle on both the flat cover and the channel wall is greater than 90°.