Which filling practice is unique to one-pound refillable cylinders?

• A. Gravity fill method, special adapter attachment is needed for dispensing equipment or dead man valve must be held open by operator
• B. Pressure fill method with standard equipment
• C. Vacuum fill method
• D. Automatic top-off fill

Answer: (A)

Gravity filling is the method used for one-pound refillable propane cylinders. It fills the cylinder by letting liquid propane flow in under gravity rather than being forced in by pressure. Because these small cylinders require a vent path during filling, a special adapter is used to connect the fill line, or the operator must hold a dead-man valve open to keep that vent path available so displaced air and vapor can escape as the cylinder fills. This setup ensures the cylinder is filled safely to about 80% of its capacity, preventing overfill and reducing the risk of venting propane. The other methods—pressuring the cylinder with standard equipment, vacuum filling, or automatic top-off—are not typical for these small cylinders and do not provide the same safe venting control required during their filling.