8-39 
 
 
8.4.1.3 Precautions for Use of Negative Pressure Ball 
Besides the seal cover, the front end of the negative pressure ball also has two check valves, as 
shown in the following figure. The embedded check valve is connected to the inlet port of the 
negative pressure ball and is used only for gas suction. The external check valve is used only for 
scavenging. If the pre-seal cover is removed or loose, the sealing performance of the negative 
pressure ball is degraded. In this case, fasten the seal cover.   
 
 
If the negative pressure ball is connected to a tested component, the negative pressure ball is used 
only for gas inlet. However, if the negative pressure ball is squeezed, the air is exhausted.   
 
In contact after fixing in the 
corresponding position 
Seal cove
 
External check valve (gas outlet) 
Fastenin
 the seal cove
 
Gas inlet