How much nitrogen is too much?

[NormChris]

If you were to over pressurize a system 90% of the time it would be the low pressure control bellows that would blow first. Or, the bellows would be damaged to the point that it would no longer operate correctly.

[will 2]

Leak test w/ vacuum pump and micron gauge.

Find the leak w/ nitrogen.

With the right tools, 100-150 PSI is plenty.

[hvacbear]

Originally posted by lmtd

Originally posted by NormChris


Those of you who are thinking that the maximum test pressures listed on the unit are somehow related to some burst pressures of the coils and piping are thinking incorrectly.

No, not thinking incorrectly at all. It is CLEARLY stated in my post the ASTM maximum WORKING pressures and I fully understand the difference and there was a time I could quote the multipliar used to develop it from the burst pressure of the weakest component, but that was a few years ago when ASME and FM codes were on the cuff.

The expansion rate and smaller molecule are key to leak testing with nitro and IMHO and training of others, I state that section above 120 psig is labeled "retard" for a reason and that reason is that only retards test above it.

How come we don’t have more coils burst then?
I have been in several buildings where the temperature was well over 110 degrees (R-22 is at 226 PSI) and the system to include the coils had equalized. I have never had a coil burst due to over pressure. The reason for using less nitrogen pressure than R-22 is nitrogen is seven times less dense than R-22 so it leaks “easier”. The retard section on a manifold gage is there simply to protect the gage not equipment.

[sparks]

I was taught that the reason you didn't pressurize a system with over 100-125psig was the possibility of bending or breaking the suction valves in the recips. I also want to see the drop, so I never let it go off of my low side scale. The 5psig increments on the high side don’t cut it for really small leaks. IMHO

[hvacbear]

Originally posted by sparks
I was taught that the reason you didn't pressurize a system with over 100-125psig was the possibility of bending or breaking the suction valves in the recips. I also want to see the drop, so I never let it go off of my low side scale. The 5psig increments on the high side don’t cut it for really small leaks. IMHO

How? if the entire system is at a uniform pressure then there should be no pressure diffrental across the valves.
Even if there is think of the diffrence between suction pressure and discharge.

[sparks]

Originally posted by hvacbear

Originally posted by sparks
I was taught that the reason you didn't pressurize a system with over 100-125psig was the possibility of bending or breaking the suction valves in the recips. I also want to see the drop, so I never let it go off of my low side scale. The 5psig increments on the high side don’t cut it for really small leaks. IMHO

How? if the entire system is at a uniform pressure then there should be no pressure diffrental across the valves.
Even if there is think of the diffrence between suction pressure and discharge.

The high (say300psig) pressure initially entering the suction side would hold open possibly breaking or bending it. The discharge valve is made to handle those pressures, but not the suction side. Ever seen them, they are made differently, lighter steel and springs.

[Edited by sparks on 08-28-2005 at 09:19 PM]

[sparks]

I’m, not trying to be a smart-ass, just trying to illustrate my point.

[hvacbear]

True but if the pressure is equal on both sides how could it hurt? I charge nitro hi and lo side and no problems. I usually use 100-150 psi but 350 hasn’t hurt so far.

Also for those of you with reservations about flare fittings. A properly made flare fitting can hold much more pressure than encountered in most HVAC systems. I replace them too because of leaks but they have their place.

[sparks]

Originally posted by hvacbear

I charge nitro hi and lo side and no problems. I usually use 100-150 psi but 350 hasn’t hurt so far.

Well, I guess I just have my own quirks then, but I also don't add nitrogen on both sides with all of the components in the loop.

I always add on the high side, my reason behind this is because I want to see the gas going through the system. This way I know there are no restrictions (bad powerhead, blocked screen or flow-rater, check valve on a heat pump).

What ever works for you is fine, as long as the end result is the same right.

[hvacbear]

I guess so.

[Timpco]

Thank's for the input,I use 100 most of the time but when
I can't find a leak increase pressure 200PSi and create one.
good point!
we can alway's learn something new if we have the right
aditude.

[cwjwh]

Never go over 150 psig. The danger is blowing the fustite on the compressor.

[luvcldair]

I go to about 140-150 psi and if i cant find a leak at that pressure i wouldnt think one is there....

Just my openion