Triple Evacuation with Nitrogen

[Quality]

nitrogen or OFN is free of oxygen which is a content of water / moisture
In lay mans terms think of swiping a dry sponge through a bath of water
it ends up wet and its easier to remove wet OFN which is moist than is is to remove pure water as the OFN carries the water

[DTLarca]

nitrogen or OFN is free of oxygen which is a content of water / moisture
In lay mans terms think of swiping a dry sponge through a bath of water
it ends up wet and its easier to remove wet OFN which is moist than is is to remove pure water as the OFN carries the water

So the nitrogen being free of oxygen has some imortance because oxygen is a component of the water molecule? I wonder how this has importance?

Does the OFN operate as a sponge or as a broom?

Why did we use, say, R22 on R22 plant, back a few decades ago, to perform a tripple vac - why did we not use OFN back then already?

[Quality]

I can not comment as I have never used R22 as purge gas

[james10]

So the nitrogen being free of oxygen has some imortance because oxygen is a component of the water molecule? I wonder how this has importance?

Does the OFN operate as a sponge or as a broom?

Why did we use, say, R22 on R22 plant, back a few decades ago, to perform a tripple vac - why did we not use OFN back then already?

The importance of N2 being oxygen free is that oxygen can react violently with oil and cause explosion

[DTLarca]

The importance of N2 being oxygen free is that oxygen can react violently with oil and cause explosion

Sure - but that statement seems to come from a position that assumes there is a real purpose and even a real need for tripple evacuation. I'm sort of asking why do so many people assume that tripple evacuation with nitrogen is even necessary.

[monkey spanners]

I'm sort of asking why do so many people assume that tripple evacuation with nitrogen is even necessary.

Sure, but what proof do you have that so many people belive this to be necessary?

I think it is left over from when single stage vac pumps were more common

Jon

[DTLarca]

Sure, but what proof do you have that so many people belive this to be necessary?

I think it is left over from when single stage vac pumps were more common

Jon

You're right - I don't have inductive evidence but rather only abductive evidence - the sort Sherlocke Holmes used as opposed to the sort an election exit pollster would use

But that seems a good point regarding single stage pumps.

But then why would they rely of triple-vac when using single stage pumps?

[monkey spanners]

But that seems a good point regarding single stage pumps.

But then why would they rely of triple-vac when using single stage pumps?

I think they used to break the vacuum with refrigerant. That way if the pump only gets out 98% on each vac by the third one there is very little air left in. I think the moisture thing is a bit of a red herring.

People also tend to think if one of something is good then more must be better.

There may be a case of people not wanting to appear lax in their working practices so they claim to do what they think or have heard is best practice. I for example never ever braze without ofn...


I have found on systems that are taking a long time to vacuuming that putting a few bar of ofn in and starting again helps speed things along, i suspect the slowness is due to refrigerant disolved in the oil and the ofn going in stirs the oil up a bit (often movement can be seen in the comp sight glass for example)

Jon

[B G Scott]

So the nitrogen being free of oxygen has some imortance because oxygen is a component of the water molecule? I wonder how this has importance?

Does the OFN operate as a sponge or as a broom?

Why did we use, say, R22 on R22 plant, back a few decades ago, to perform a tripple vac - why did we not use OFN back then already?

A long time ago all the refrigerants were Cheap in todays terms.
Also the triple evacuation was also described as a dilution method for large systems.
You must appreciate that Vac pump are so much better than they were years ago.
You might not appreciate this but when most commercial plant was open drive we did not have vac pumps, we used the system compressor to evacuate the system.
On large systems it was not possible to reduce moisture to the level we now consider acceptable and the triple or dilution method was the industry norm.
It meant reducing the system to the lowest vacuum you could achieve and adding refrigerant to absorb non condensible and then evacuate again the dilute the residual non condensible constituents.
Don't forget we did not know then that we were environment criminals, it was we all did.
It was the norm to vent service cylinders to reduce the pressure so you could recharge them.

How time change.