Pressure testing and evacuation?

[itsiceman]

I try and dig up the tire info

[jayguy]

The Additel 680 is reasonable just under $500. Not like we don’t already pay $375 for a micron gauge.

I just think there’s more to the pressure test that we’re not exploring. For instance when a system is pressurized we need to purge out all of the standard air inside due to a potential greater change than N2 alone. Also, when pressurizing we create heat of compression on the gas inside the system. The process begins and transfers heat to the surrounding surfaces. So, is a pipe temp clamp going to give us the results we’re looking for or do we need a temperature sensor built in? I guess we can wait several minutes for the heat of compression to balance with the tubing, but who has time to wait?
I find it odd that we’ve gone off the deep end with vacuums, but yet still use a standard gauge to pressure test with marginal results. So, before I drop $500 on another gauge, I want to explore the art of pressure testing just like we have with the art of vacuums.

True but how accurate do you want to get? Time is your friend and is never considered in most formulas. You can get all temperature-compensated you want but if you aren’t going to wait for the ambient temperature to change, what’s the point Even with time, temperature accuracy is just as important and have you considered the change in system volume with a change in temperature? With a more accurate sensor, you will probably see MORE things change and it may seem less stable. Aren’t we just trying to get to a point where we feel reasonably comfortable with the system being leak free?

[itsiceman]

Not me. I don't install leaks

[mgenius33]

The pressure in the system will always be lower than when you started you wouldn't be adding heat.

You are adding heat because you are adding pressure to a vessel. The N2 initially transfers heat of compression to the vessel. As the ambient air draws that heat, it reduces both the vessel and N2 temperature. This reduction in turn slightly reduces pressure. This is why the pressure change is greater initially and then decays.
The opposite is true for the tank that is reducing pressure. The vessel warms the N2, then the ambient air warms the vessel. This will slightly increase the pressure of the tank. The tank doesn’t get cold because of evaporative cooling, it’s due to pressure change.

I don't think there would be a way to keep track of temperature that close especially on a split system.

The issue we have is the vessel can be in several different ambient conditions, so yeah that throws a wrench into the program.

True but how accurate do you want to get? Time is your friend and is never considered in most formulas. You can get all temperature-compensated you want but if you aren’t going to wait for the ambient temperature to change, what’s the point Even with time, temperature accuracy is just as important and have you considered the change in system volume with a change in temperature? With a more accurate sensor, you will probably see MORE things change and it may seem less stable. Aren’t we just trying to get to a point where we feel reasonably comfortable with the system being leak free?

The temperature compensation should always be used on a pressure test for accuracy. Having a gas temp sensor instead of a vessel temp sensor should offer more accuracy, but yeah cost goes along with that.

Like I said, there’s a lot more to this pressure test stuff. I’m just wondering why we’re overboard with vacuums, but do little with pressure tests. We could hold vacuums over night too, but we don’t have that kind of time typically. So, we buy a BluVac and watch the decay to help estimate that the final vacuum will be good.

[itsiceman]

I guessed it would be a net loss. I'll have to set up a little test and maybe learn something.

[mgenius33]

Energy is always conserved.

[mgenius33]

I guess I will have to be more patient and simply wait the 15 min for stabilization before starting a compensated test.
Then use Charles law to solve. Since volume isn’t changing we insert pressure. P1psia/T1°K=P2psia/T2°K

Or make it easy on myself and just use Measurequick.

I think most if not all of the temp compensated gauges I’m looking at are ambient temperature not internal gas temperature.

[SoFlaDave]

My typical method is, if its a brand new install, N2 pressure test my 550's in the morning and change hose o-rings (treated with nylog) if there's more than than .5 PSI drop within 5 min. Once on the system ignore any variance less than .5 psi per minute until 20 min passed and reset the pressure test. If it drops by more than the initial pressure test on the gauge set alone within 5 min that's probably a leak. Alternatively I will use my smart probe alone to eliminate as many connections as I can.

For repairs, I will pressure test and bubble check my joints and if they pass start the vacuum and keep fingers crossed. If the vacuum plateaus at above 500 I will make a note of it and recommend a leak search but start the system. If it plateaus above 2000 microns I will let the customer know there is a leak in the system, note it on the ticket and let them decide whether they want it operational.

[mgenius33]

I guess I will have to be more patient and simply wait the 15 min for stabilization before starting a compensated test.
Then use Gay-Lussacs law to solve. Since volume isn’t changing we insert pressure. P1psia/T1°K=P2psia/T2°K

Or make it easy on myself and just use Measurequick.


I think most if not all of the temp compensated gauges I’m looking at are ambient temperature not internal gas temperature.

Correction

[mgenius33]

My typical method is, if its a brand new install, N2 pressure test my 550's in the morning and change hose o-rings (treated with nylog) if there's more than than .5 PSI drop within 5 min. Once on the system ignore any variance less than .5 psi per minute until 20 min passed and reset the pressure test. If it drops by more than the initial pressure test on the gauge set alone within 5 min that's probably a leak. Alternatively I will use my smart probe alone to eliminate as many connections as I can.

For repairs, I will pressure test and bubble check my joints and if they pass start the vacuum and keep fingers crossed. If the vacuum plateaus at above 500 I will make a note of it and recommend a leak search but start the system. If it plateaus above 2000 microns I will let the customer know there is a leak in the system, note it on the ticket and let them decide whether they want it operational.

Vacuum plateaus at 2000 could just mean there’s refrigerant under the compressor oil or accumulator, or a lot of moisture. While it can also indicate a leak, it’s a simple guess. The whole point of this post is, we’ve exhausted vacuum tests and have a very reliable way to help ensure a dry system, but we don’t have a reliable gauge to pressure test. A gauge that will allow us to calculate out the variables. Instead we rely on the secondary form of leak testing by using a vacuum gauge that isn’t really designed to perform this task.

[m singer]

You are adding heat because you are adding pressure to a vessel. The N2 initially transfers heat of compression to the vessel. As the ambient air draws that heat, it reduces both the vessel and N2 temperature. This reduction in turn slightly reduces pressure. This is why the pressure change is greater initially and then decays.

I think you just explained why I have been seeing slow pressure decays on short time standing pressure tests.

[SoFlaDave]

Honestly if manufacturers could manage to make equipment that isn't almost certain to leak in less than 5 years it might be worth the kind of R&D and initial cost for the high precision pressure testing that we're talking about, but those days are over and never coming back.

[mgenius33]

Honestly if manufacturers could manage to make equipment that isn't almost certain to leak in less than 5 years it might be worth the kind of R&D and initial cost for the high precision pressure testing that we're talking about, but those days are over and never coming back.

Yeah, that’s no lie right there!

[jayguy]

Honestly if manufacturers could manage to make equipment that isn't almost certain to leak in less than 5 years it might be worth the kind of R&D and initial cost for the high precision pressure testing that we're talking about, but those days are over and never coming back.

If they did that, would we really need high precision pressure testing tools?

[TruTech-Bill]

"Three ways to view via new larger backlit LCD screen, easier to read and the dot-matrix display shows more info including:

bar graph
rate
rate meter"[/I]

I'm not sure what that means. I'll have to look into it. I'm thinking 'rate' doesn't refer to Leak Rate, but microns per second and a graph for easier determination of where you're at micron-wise.[/QUOTE]

@vin lashon

I looked it up and added detail to the listing on the TruTechTools site just now:

bar graph - graphical illustration of the measurement. uses a non-linear scale for better resolution at deeper vacuum (Full bars are atmospheric pressure.)

rate - the running 10 sec average of the measurement change per minute. (Negative rate indicates deeper vacuum.)

rate meter - graphical illustration of the measurement's real-time change (The scale is dynamic, that is not the actual value)


Sent from my iPhone using Tapatalk

[mgenius33]

So, I used the 10 min wait, and temperature compensated test today. Of course pressure didn’t move @309.6psig, not even 1/10°.