Simple question I can't figure the answer to...

[Harry P.]

So why do some (not all) brands/types of spray paints have a tiny pinhole on the top of the cap? What possible function does this tiny hole serve, especially since it's only on some cans of spray paint, but not all?

[Belugawrx]

The question may be simple, Harry,....

......but the answer, is ,... 

 

 

 

Have you taken your Meds ?

Probably something to do with the type of injection molding the company that makes the caps uses

 

[Greg K]

i remember grabbing a cap to spray some paint in to do some detail work, and that BLAH_BLAH_BLAH_BLAH cap had a pin hole in it and leaked all over the table!

[disabled modeler]

That is probably why it does have one in it...so it cant be used for other uses?...I have done the same thing before Greg but got paint everywhere.

[Harry P.]

  On 12/13/2015 at 11:10 PM, Greg K said:

i remember grabbing a cap to spray some paint in to do some detail work, and that BLAH_BLAH_BLAH_BLAH cap had a pin hole in it and leaked all over the table!

Yes, exactly! It's happened to me... so I got to wondering what the heck that little hole is there for anyway?

[Greg K]

  On 12/13/2015 at 11:23 PM, Harry P. said:

Yes, exactly! It's happened to me... so I got to wondering what the heck that little hole is there for anyway?

i had a feeling this was where you were headed Harry. put a piece of tape on both sides of that hole 

[Harry P.]

I actually noticed the little hole a long time ago, and now I always tilt the cap when I spray paint into it so that the hole is at the upper side of the cap and the paint collects on the lower side.

But after all this time I still can't figure out why the hole is there in the first place.

[angelo7]

To avoid building pressure inside the cap area?????

[Harry P.]

  On 12/13/2015 at 11:51 PM, angelo7 said:

To avoid building pressure inside the cap area?????

The only way pressure could build there is if there was a leak somewhere in the top of the can. And even then, the seal on the snap-on cap isn't airtight anyway, so that can't be the reason.

[62rebel]

possibly to keep the cap from popping back off after it's put on? there could be a circumstance where it could happen, I suppose

[vettecote]

Some engineer thought "lets put a hole in it and see if anyone notices"...Joe

[1930fordpickup]

If the cap does not have a pry slot to open, the air needs to be able to escape when the cap  is placed on the top in the factory and in your home. As Curt posted earlier.

It may also be placed in the cap so that it will come out of the mold easier because of vacuum and surface tension. 

[Harry P.]

  On 12/14/2015 at 12:10 AM, 1930fordpickup said:

If the cap does not have a pry slot to open, the air needs to be able to escape when the cap  is placed on the top in the factory and in your home.

Like I said, the snap-on cap's seal isn't airtight in the first place. Any pressure that needed to escape could easily escape where the cap meets the can.

And besides, a properly manufactured spray can doesn't leak.

I find it hard to believe that the little hole is a "safety valve" to let pressure escape. But hey, who knows? Maybe it actually is just that. But I need to hear it from someone who knows the real reason before I believe it.

[Rob Hall]

To release pressure when there are atmospheric changes due to altitude? 

[Harry P.]

  On 12/14/2015 at 12:21 AM, Rob Hall said:

To release pressure when there are atmospheric changes due to altitude? 

But the fact is that only some cans have the hole... some don't. But obviously all spray cans are under pressure, so that doesn't explain it.

[Rob Hall]

  On 12/14/2015 at 12:23 AM, Harry P. said:

But the fact is that only some cans have the hole... some don't. But obviously all spray cans are under pressure, so that doesn't explain it.

Maybe it's just one of those mysteries of life that can't be explained.   Maybe you have too much free time to ponder things like this...

[martinfan5]

Ive actually wonder this myself as well.

[Ace-Garageguy]

Here are two sites that agree about the venting to accommodate changes in atmospheric pressure idea...

https://www.scienceabc.com/pure-sciences/why-spray-can-lids-have-a-small-hole-on-top.html

http://science.howstuffworks.com/innovation/science-questions/question107.htm

...and a site that sells the caps with what they call "vent holes"...

http://mckernan.com/store/Aerosol-Caps

 

[XJ6]

Anytime Done spray painting with a Can tip Can up side down to Clear Nozzle that Pin hole helps keep the Nozzle Clear ??

[Harry P.]

Interesting... but since the seal between cap and can isn't airtight, I don't see the need. And even more puzzling, only some cans have the hole, not all.

[Ace-Garageguy]

  On 12/14/2015 at 12:50 AM, Harry P. said:

Interesting... but since the seal between cap and can isn't airtight, I don't see the need. And even more puzzling, only some cans have the hole, not all.

Apparently there are differences in design from manufacturer to manufacturer, some being airtight-enough to warrant the hole.

I've noticed lately that more caps seem to lack the hole, so maybe its real usefulness has been found to be nil.

[Harry P.]

Thanks, Bill. Another one of life's little mysteries solved..

[Skip]

Could be when the spray cap is placed onto the can during assembly that there is some expectation of pressure build up   underneath the cap which could cause it to pop off.  The possibility of the presence of liquid paint under the cap could cause enough hydraulic pressure to pop off the spray cap.  

Good question, but you can guess that either some mechanical engineer, manufacturing tooling person had it placed there for a reason.  It costs money for the tooling to place that hole there so the manufacturer of the cap isn't going to just put a hole in the cap  without a good reason.  Something like, indexing the cap so that the small round spray nozzle can be pressed in.  Even for a pin to eject the spray cap from the injection mold.  You could probably think up a bazillion such scenarios, until you break down the steps of the manufacturing process from beginning to end  all it would be is a guess.

[SfanGoch]

  On 12/14/2015 at 1:17 AM, Harry P. said:

Thanks, Bill. Another one of life's little mysteries solved..

This is worthy of discussion equal to, and even surpassing, the mystery of why suits are packed in garment bags and garments in suitcases. I'm sure Leonard Nimoy would've found the answer to this perplexing anomaly if only "In Search Of.."was renewed for one more stinkin' season.

[Harry P.]

  On 12/14/2015 at 1:55 AM, SfanGoch said:

This is worthy of discussion equal to, and even surpassing, the mystery of why suits are packed in garment bags and garments in suitcases.

Or why we drive on the parkway and park in the driveway?

Sorry to bother you with such a minor triviality. Feel free to ignore this thread...