Expanding foam applicator gun

I’m in the process of insulating a room internally and so thinking of getting a gun for expanding foam. Is it possible to take the can off while there’s foam in the can? ie do the cans have valves, and can you expect to be able to use the foam again after a while? Obviously the gun would need cleaning. Part of the reason for the question is that I might want to have two cans of foam on the go (normal and low expansion).
I had a look in the wiki but didn’t see an answer.
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Jón Fairbairn snipped-for-privacy@cl.cam.ac.uk
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On Monday 25 March 2013 10:54 Jon Fairbairn wrote in uk.d-i-y:

Yes and yes - although older guns sometimes IME get a bit of dried foam in the ball valve where it attached to the can - this allows slow escape of foam and required blowing the gun through with cleaner if leaving off (or the foam is liable to harden in the gun).
The cans are OK left off if you squirt a bit of cleaner over the nozzle.

If you are just swapping from one to the other the gun does not need cleaning - just the can (above).

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Thanks, both. I’ve made mention on the wiki; I hope an accurate summary but you might want to check.
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Jón Fairbairn snipped-for-privacy@cl.cam.ac.uk
http://www.chaos.org.uk/~jf/Stuff-I-dont-want.html (updated 2012-10-07)
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On 25/03/2013 10:54, Jon Fairbairn wrote:

IME you are better not taking the can off the gun unless you need to. It will stay usable for quite some time by simply clearing any foam off the end of the nozzle prior to next use. (note however this may vary with gun quality and variability - others have not had the same success as me with this).
If you take the can off the gun, the can does have a valve (but probably no better than the one on a "normal" can - so don't expect a started can to last that long if left unused. You will also need a can of cleaner to flush the gun through.
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On Mon, 25 Mar 2013 13:47:02 +0000, John Rumm

I picked up and used a gun that hadn't squirted any foam out of the nozzle for six months, since I last used it in the back room walls/insulation. It was fine - just cleared off the end, turned the knob and pressed the trigger.
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On 25/03/2013 10:54, Jon Fairbairn wrote:

Yes .. if attaching to another can of foam no problem ... if not going to use for some months better to clean .... attach it to a foam cleaner car and spray until clean.
Be warned make any changes outside ... neighbour did this but ball valve had stuck so it sprayed everywhere, and the more he tried to reattach the gun the worse mess, in the end he just left in on the floor - it seemed to be expanding for Hrs. He hands arms & hair were hell of a mess ... and as you know it don't come off easily.
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On 25/03/13 10:54, Jon Fairbairn wrote:

I cut kingspan seconds with a wood saw and weld them together with pinkgrip, leaving the half used can attached to gun for days, Not using the yellow expanding stuff any more [g]
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On Tuesday, March 26, 2013 12:31:38 AM UTC, snipped-for-privacy@hotmail.com wrote:

I had a can of drywall fixing foam on a gun and used it for its intended purpose, but since I had some left, I am now using it for general expanding foam applications. It is low expansion and a bit stickier and more dense th an normal expanding foam, which is usually an advantage. Presumably it is more or less the same as the low expansion window fixing foam.
Simon.
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