Scott Davies from JAVAC recommends the push/pull method of refrigerant recovery.
We all know that the best method is to take the refrigerant out as vapour because this leaves the oil behind, but it’s very slow and works against itself by freezing the plant and heating (pressurising) the cylinder. The now famous “Push-Pull” method is the fastest way but believe me you may be surprised as to how little it is used. The first reason is that it’s not accessible on some plant if a liquid connection is not available. The other reason is many people have not grasped the “Push-Pull” technique.
This causes a pressure drop in the cylinder and a differential between the cylinder and the plant. The liquid has only one option, and that is to race into the cylinder as fast as the hose size will let it.
That’s the pull bit done – but what about the high-pressure discharge from the recovery unit?
So what we will see initially is a steady rise in the cylinder weight. It then accelerates as the recovery unit discharge increases the temperature and pressure in the plant. If we can swap the cylinders fast enough, 200-250kg/hour is achievable with any recovery unit.
It would be a very rare breakdown that would cause the compressor oil to deposit itself in the refrigerant. If a substantial amount of oil does end up in the recovery cylinder the recycling companies won’t like it. However it can be dealt with effectively.
It might be an idea to fit a sight glass, valve and tee piece between the recovery cylinder and plant. We can then let the cylinder settle (preferably in a warm area).
We then recover any vapour from the recovery cylinder with our recovery unit leaving the oil behind. Getting the oil out of the cylinder is simple – just pressurise the vapour side with OFN and run the oil off into a bucket via the liquid port.
How we recover refrigerant is up to us but push/pull has another great advantage; its saves wear and tear on our recovery units. It is a difficult task producing a reliable lightweight unit at a cost effective price. So if we look after them it saves us time and money.