The best method of prevention is simply to never overfill reusable cylinders.
To assist the technician when recovering refrigerant into reusable cylinders, two types of shutoff devices have been developed and approved:
External independent protection
In-cylinder integral protection
Eternal Independent Protection
External independent protection systems are weight and scale-type systems.
There are two types of scales:
One is calibrated to visually indicate to the technician that the cylinder is 80% full
Another shuts down the system when the cylinder is 80% full by weight
External Independent Protection
External independent protection systems have one major disadvantage.
The scales used are generally calibrated to the weight of virgin refrigerant.
When refrigerant is recovered, it is usually from an operating system which contains oil.
The weight of oil is usually between 15% to 20% less than the weight of virgin refrigerant.
The result is the scale calibrated to weigh virgin refrigerant may read 80% full when in fact the cylinder could be 100% full by a blend of refrigerant and oil.
In-Cylinder Integral Protection
The in-cylinder integral protection system has an 80% shutoff device (overfill protection device) that physically measures the volume of liquid refrigerant in a cylinder to 80%, whether it is a virgin refrigerant or blended with refrigerant oil.
Since these systems are highly reliable, shutoff devices have been incorporated by a majority of refrigerant recovery equipment manufacturers.
It must also be noted that this equipment is designed to operate only with reusable cylinders equipped with integral overfill sensors.
The integrated sensor most commonly used is the float-type liquid level switch.
In addition to providing positive volumetric overfill protection, this device has the advantage of being integral to the reusable recovery cylinder.
Cylinders equipped with this device are recognizable by a quick disconnect electrical terminal located near the valve.
Operation of Integral Overfill Switch
Integral overfill switches on recovery units generally operate as follows:
The overfill level switch, which is mounted within the empty cylinder, is connected to the recovery equipment with a quick disconnect cord set
The overfill level switch, which is a normally closed switch, completes an electrical circuit to the recovery/recycle equipment, allowing it to operate
When the refrigerant level in the cylinder reaches 80%, the float (which is an integral part of the overfill level switch and has been rising with the level of the recovered liquid refrigerant) opens the overfill level switch, automatically de-energizing the recovery/recycling unit until the 80% full cylinder is replaced.
Cylinder Handling Tips
Whenever possible, use only cylinders equipped with overfill protection
When exchanging a cylinder with an overfill protection device, insist on receiving another exchange cylinder equipped with the same protection device
Non-refillable cylinders are equipped with a one-way valve
They must never be used to recover refrigerant or used as a storage cylinder for pressurized air
Non-refillable cylinders are constructed of light gauge steel and are not approved for reclaiming refrigerants or storing air under pressure
Empty cylinders must have the heel recovered for safety and environmental reasons
A cylinder containing a small amount of refrigerant is as dangerous as a full cylinder
Empty cylinders must be evacuated prior to refilling
Proper identification of cylinders is essential
Those containing a mixture of refrigerant gases or foreign material cannot have the refrigerant reclaimed
A cylinder that has lost its identification markings must be immediately tagged with an approved WHMIS label
Cylinder valves must be leak-free when in the closed position
If a refrigerant valve is suspected of leaking, leak test the valve using a soap solution
Refrigerant Cylinder Safety
Use appropriate cylinders (refillable)
Never drop refrigerant cylinders
Never apply live steam or a direct flame to a cylinder
Do not attempt to repair cylinder valves
Never refill old-style disposable cylinders
Always open cylinder valve slowly
Always close cylinder valve after each use and replace protective cap on the valve outlet
Never by-pass the overfill safety protection provided on recovery or recycling equipment
Keep protective hood on the cylinder when not in use
Never use a rusted or deteriorating cylinder (Return to the wholesaler for disposal)
Always recover refrigerant immediately from an overfilled or leaking cylinder
Do not remove or alter cylinder markings
Do not tamper with safety devices on cylinders
Do not fill refrigerant cylinders containing a virgin refrigerant more than 80% of its capacity by weight
Caution should be exercised when recovering contaminated refrigerant into a cylinder as it weighs less by volume than virgin refrigerant
A good rule to follow is to fill a cylinder that does not have overfill protection to 70% of its capacity when the refrigerant contains a lubricant or a refrigerant of an unknown quality
Always keep refrigerant cylinder secured in an upright position