Recovery Cylinder Overfill During a Chiller Decommission
A technician is decommissioning a small air-cooled chiller that holds 18 kg of R-134a. The only recovery cylinder on site is a 25 kg water-capacity cylinder with a tare weight of 14 kg and a marked gross weight that the technician cannot read because the stamp is corroded. The technician plans to recover the full charge into this one cylinder, then transport it to the depot. Ambient temperature is 28 C and rising. The recovery machine has a cut-out at 38 bar. The technician has a scale but no spare cylinder, and the depot is a 40-minute drive away.
1. Assess whether the single cylinder can safely hold the full 18 kg charge and explain the reasoning.
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The cylinder cannot be assumed to hold 18 kg safely. Recovery cylinders are rated by water capacity, and the safe fill limit is a fraction of that water capacity, commonly around 80 percent by mass of water for the refrigerant in question, adjusted for the refrigerant's density. With a 25 kg water capacity, the nominal fill limit is roughly 20 kg of water-equivalent, but the actual mass limit for R-134a depends on its liquid density at the reference temperature, and the marked gross weight is the authoritative figure. Because the stamp is corroded, the technician cannot verify the limit and must not guess.
The conservative approach is to treat the cylinder as unverified. Recovering 18 kg into a cylinder whose limit cannot be read risks overfilling, and an overfilled cylinder with no vapour space can become hydraulically full as it warms, with rapid pressure rise. The 38 bar cut-out on the recovery machine is a pressure safeguard, not a fill-limit safeguard, so it does not make the plan safe. The technician needs either a readable gross weight or a second cylinder before starting.
2. Describe how the technician should manage the recovery to avoid overfill, given no spare cylinder.
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With no spare cylinder, the technician should recover in stages and use the scale continuously. The first stage fills the cylinder to a mass the technician can justify from the legible tare and any available documentation, stopping well short of any estimated limit. The cylinder is then weighed, the recovered mass recorded, and the cylinder set aside to stabilise while the technician works on the remainder of the circuit. If the circuit still holds refrigerant and the cylinder is approaching a defensible limit, recovery must stop and the remaining refrigerant left in the system until a second cylinder arrives.
The technician should also keep the cylinder out of direct sun and monitor pressure, because a warming cylinder with a high fill fraction will show a rising pressure that signals the margin is shrinking. The recovery machine's cut-out is a backstop. The controlling measurement is mass on the scale against a limit the technician can actually read, and where that limit is unknown, the technician must err on the low side and accept a second trip rather than risk an overfill.
3. The technician decides to transport the partially filled cylinder to the depot and return for the rest. What checks and documentation should accompany that decision?
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Before transport, the technician should confirm the cylinder valve is closed, the cylinder is secured upright, and the mass is recorded and within the limit the technician has adopted. The cylinder should be labelled with the refrigerant identity and the recovered mass, and the corroded stamp should be noted as a defect so the cylinder is not returned to service without inspection. Transport rules for pressurised refrigerant cylinders, including ventilation and securing, should be followed.
Documentation should record the system, the refrigerant, the mass recovered, the mass remaining in the system, and the reason the job was left incomplete. The technician should also flag the unreadable gross weight to the depot so the cylinder is either re-stamped, recertified, or retired. Leaving refrigerant in the system is acceptable only if it is contained and the return visit is scheduled; venting the remainder to save a trip is not. The decision to split the recovery is sound only if the records make the remaining charge and the cylinder condition traceable.