Overfilling these cylinders can create a potential hazard. To prevent overfilling, recovery cylinders should not be filled to more than 80 percent of their internal volume. Most technicians accomplish this by placing the recovery cylinders on an electronic scale and monitoring the weight of the cylinder during the recovery process. When the cylinder reaches a weight equal to 80 percent of its total capacity, the technician stops the recovery process and changes cylinders if needed.
In order to use this method effectively, a technician must know the cylinder’s weight equal to 80 percent of its maximum capacity. This maximum weight will vary slightly as different refrigerants are used in recovery cylinders and different refrigerants have different liquid densities.
1. Find the recovery cylinder manufacturer’s published data for various refrigerants.
2. Calculate this value.
To determine this value, use the following procedure:
1. Calculate the internal volume of the recovery cylinder being used. This can be accomplished by dividing the water capacity of the cylinder by the density of water, which is 62.5 pounds/cubic foot. The water capacity of a recovery cylinder normally is stamped on the outside of the cylinder. For example, if a recovery cylinder has a water capacity of 47.17 pounds, then its internal volume will be 0.75 cubic feet (47.17 pounds ÷ 62.5 pounds/cubic foot = 0.75 cubic feet).
2. For the refrigerant to be recovered, determine its liquid density at a saturation temperature of 130°F. Refrigerant manufacturers publish the various saturation properties of their refrigerants, including liquid density at various saturation temperatures. For example, if R-134a were to be recovered, its liquid density at a 130° saturation temperature is 67.46 pounds/cubic foot.
3. Determine the tare weight of the recovery cylinder, which is the weight of the cylinder if it were empty. This is also stamped on the outside of the cylinder. For example, for a nominal 50-pound recovery cylinder, the tare weight would be 24 pounds.
4. Use the following formula to determine the maximum cylinder weight:
Maximum cylinder weight = (cylinder volume x liquid density of the refrigerant at 130°F x 0.80) + tare weight
For example, if the cylinder is holding R-134a, (with its liquid density of 67.46 pounds/cubic foot at 130° saturation temperature) had a water capacity of 47.17 pounds and a tare weight of 24 pounds, the maximum cylinder weight would be:
Cylinder volume = water capacity ÷ density of water (62.5 pounds/cubic foot)
Cylinder volume = 47.17 pounds ÷ 62.5 pounds/cubic foot = 0.75cubic feet
Maximum cylinder weight = (0.75 cubic feet x 67. pounds/cubic foot x 0.80) + 24 pounds = 64.48 pounds.
A technician should not continue to fill this recovery cylinder once its weight has exceeded 64.48 pounds. Again, overfilling a recovering cylinder can lead to very serious injury.
Publication Date: 12/03/2007