Recovery Cylinder Beyond Its Fill Limit With Unknown Contents
It is Friday 17:40 and the workshop is closing. The only R134a recovery cylinder stands on the scales in the cylinder store, which is at 33 °C. The cylinder is stamped with a tare of 9.1 kg and a maximum fill of 10 kg. The scales read 19.9 kg gross, so it holds about 10.8 kg of recovered refrigerant. Its gauge shows 12.5 bar; saturated R134a at 33 °C is about 7.4 bar gauge. The contents were recovered that afternoon from a twelve-year-old imported vehicle with no service history, whose owner mentioned that a friend had 'topped it up a few times with whatever was in the shed'. A Saturday technician wants to use the cylinder to charge a 2015 van booked in tomorrow morning because the bulk R134a drum is nearly empty and a delivery is not due until Monday. There is no refrigerant identifier on site and laboratory analysis takes five working days. A spare empty recovery cylinder is available.
1. Diagnose the condition of the cylinder and the gas in it, and state what should be done tonight.
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Three separate problems, each sufficient on its own.
- Overfill. Gross 19.9 kg minus tare 9.1 kg gives 10.8 kg of liquid against a 10 kg maximum fill - 108 % of the limit. Recovery cylinders are limited to about 80 % of water capacity to leave an expansion space; overfilling means liquid, not vapour, reaches the pressure relief device, and a warm store can then hydraulic the cylinder or lift the relief valve.
- Pressure above saturation. At 33 °C, R134a sits at roughly 7.4 bar gauge; this cylinder shows 12.5 bar. About 5 bar of excess pressure points to non-condensable gas - almost certainly air drawn in during a poor recovery, or a different refrigerant entirely.
- Unknown and possibly mixed contents. 'Topped up with whatever was in the shed' raises the possibility of a hydrocarbon or an incompatible HFO blended in. Mixing means the gas cannot be recycled to any known specification.
Tonight: close and cap the valve, keep the cylinder upright, move it out of the warm store into the coolest secure area, label it clearly 'UNKNOWN - DO NOT USE - DO NOT VENT', inform the supervisor, and do not load it into a van. An overfilled or non-compliant cylinder must not be transported; it needs to be brought within limits by transferring liquid into the spare cylinder, weighed continuously, before any movement.
2. Explain why on-site recycling cannot make this gas usable, and what labelling, paperwork and transport arrangements must accompany it.
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Why recycling will not fix it A recovery machine's filter-drier and oil separator remove moisture, acid and particulates. They do not remove air, and they do not separate one refrigerant from another. Passing this gas through the machine would give clean-looking gas with the same 5 bar of non-condensables and the same unknown composition. Non-condensables raise discharge pressure and temperature, cost cooling performance and can trip high-pressure protection; a mixed or hydrocarbon-contaminated charge changes oil behaviour and creates a flammability question in a system never designed for it. The only routes are certified reclamation or destruction.
Labelling and paperwork
- Cylinder label: 'Waste / for analysis - contents unknown, suspected non-condensables', recovery date, workshop, approximate mass, and the vehicle it came from.
- Refrigerant log entry recording recovery, the transfer between cylinders, weights before and after, and the decision to send for analysis.
- A hazardous-waste transfer note and a reclamation contractor who will issue an analysis report, kept with the job records.
- Transport: this is dangerous goods in an overfilled, incorrectly labelled cylinder - the transfer must happen first, the cylinder must be within its fill limit, valve capped and the paperwork must match the actual contents before it leaves site.
The point to carry into the exam: recovery, recycling and reclamation are three different activities with three different limits, and a machine on the bench cannot upgrade a contaminated charge.
3. The owner of the Saturday van arrives and is told the workshop cannot charge it. How do you handle the workshop and the customer, and how should the remaining refrigerant be recovered from the van safely?
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Dealing with the situation Do not charge the van from the suspect cylinder. The van is an R134a system needing a known, correctly specified charge; using mixed or air-contaminated gas would transfer the fault to a vehicle that did not have one, and there is no paperwork trail that would protect the workshop. Options, in order of preference: offer the customer a later appointment when the bulk drum lands on Monday, or obtain reclaimed R134a from an approved supplier with a certificate of analysis today. If the van is not needed until next week, book it and hold the slot. Tell the customer plainly what happened, that it is not their fault, and what you are doing about it; do not blame the previous vehicle's owner in front of them.
Recovering from the van
- Weigh the recovery cylinder before starting and know its remaining capacity: at 10.8 kg it has none, so use the spare cylinder.
- Connect to both service ports, recover vapour first to avoid dragging liquid/oil slugging the machine, then liquid, and monitor the scale continuously.
- Stop at the cylinder's rated fill and swap cylinders if needed rather than 'just a bit more'.
- Pull the system down, check the machine has reached its usual vacuum, and record the recovered mass.
- Never vent the van's charge to atmosphere and never use the van's system to 'take' contaminated gas from elsewhere.
Finally, put the workshop procedure under review: a weekly cylinder weigh-in and a fill-limit card on every cylinder would have caught this before 17:40 on a Friday.