Gas/water valve with backflow prevention for medical devices

A gas/water valve assembly for a medical device, the gas/water valve assembly comprising:

• a valve well having a gas outlet;
• a shaft positioned in the valve well, the shaft having an outer surface, the shaft comprising:
• a first opening;
• a second opening;
• a third opening configured to align with the gas outlet;
• and
• a bore extending from the first opening to the second opening, the bore being in fluid communication with the third opening;
• and
• a seal assembly extending less than an entirety of a circumference around the shaft, the seal assembly configured to selectively block fluid from traveling between the third opening and the gas outlet.