Top Answers
1. Tire (Almost everyone has a car, and everyone knows tires have valves!)
2. Water Pipe (Common in homes and easy to picture)
3. Heart (Less obvious, but it's technically a pump with valves)
Other Possible Answers
* Toilet Tank
* Fire Hydrant
* Canned Goods (Pressure valves)
* Balloon
* Gas Tank
Remember, the key is to pick things that are familiar and easily understood by a broad audience.