I have a so-called heavy duty cartridge gun like this
If you look at it again you'll see an annular recess and a locking lever on the front end. The back end of the tube itself fits into that and then clamps into place so no need for a skeleton holder for the front end of the tube. The bung is an airtight seal rather than just a piston so it can reverse action and pull the sealant back into the tube.
-- "I found this stone in the park yesterday. It's been worn to a perfect sphere by the elements and dimpled by time." "Harry, that's a golfball!" (3rd Rock From The Sun)
That's all well and good, but, if you remove a half used tube from this gun, won't this result in it sucking in loads of air!?
Sparks...
Why?
As you said
"The bung is an airtight seal rather than just a piston so it can reverse action and pull the sealant back into the tube."
So if you pull the bung out, as it is an air-tight seal, won't it pull air into the tube?
Sparks...
I'm still not really sure what you're trying to say. The back end of the tube has its own airtight(ish) cap anyway regardless of what type of gun you use. If that wasn't there all the sealant would run out on to the shelf in the shop!
At the front end of the tube and nozzle of course you'll pull air back in but that's the point. To empty the nozzle so you can put a sealed cap back on and not have a nozzle full of rock hard sealant next time you use the tube. I can't see me paying 15 squids for the privilege but I've spent plenty of time firkling around in tubes of silicone with little screwdrivers trying to clear the nozzle and front end of the tube of the stuff that's already set. Not an issue if you use a lot of the stuff and on a regular basis but handy if a single tube lasts you for months.
-- "I found this stone in the park yesterday. It's been worn to a perfect sphere by the elements and dimpled by time." "Harry, that's a golfball!" (3rd Rock From The Sun)
I looked at this at the SF trade counter, wasn't convinced and bought the pneumatic one instead. That certainly works.
Okay...
The tube holds (say) 500ml.
You use 300ml
When you pull the plunger out of the back, 300ml of air is pulled into the gun via the nozzle.
With a normal gun this does not happen.
Is this going to cause the remaining (or part thereof) sealent to set in the tube, now it has air mixed with it?
Sparks...
Is that the 40 quid one which needs a compressed air supply?
Ok, I see what you mean now. The solution is very simple. If you actually want to remove a part used tube you put the cap back on or your finger over the end before you remove the plunger.
But how does air get into the gap between the cartridge piston and the airtight piston on the gun to allow the air tight piston to be withdrawn from the cartridge body?
Yep.
Roger? I have such a device - bought off QVC - the tube is held by a circular latching ring at its rear end (it's the shiny part of the pistol-grip). Once the cartridge tube had been inserted it's very firmly held. The trigger mechanism is easy to use -an its plunger pushes the goo out the front just like the old-fashioned frame type- however the handle has the facility to withdraw the plunger ; practically this means that one can 'suck-back' the goo. No more blobs of goo dripping and oozing out of the nozzle . Effectively this means that one can swap different tubes easily and having re-capped a partially used tube, it can be used again. Apparently one can purchase 'sausages' of goo that can be inserted into an empty cartridge - but I haven't performed this 'trick' yet. This mechanism is easier to use than either of the frame-types I've used before, is indifferent to the length of the cartridge used - [You realise that cartridge come in different lengths? - and doesn't seem to pinch the web, of skin, between thumb and fingers! I heartily endorse it.
Three obvious benefits struck me with the first post and, further down the thread, the thickness of D-I-Y-ers that don't yet understand the concept of lids, struck me.
4 occurred to me writing 3: Any messed runs or glitches can be unlaid to a certain extent. If not salvageable, removable.
But of course it might be a Draw-Back.
Thanks for the detailed explanation Brian.
Like others, I'm still curious to know how you remove the plunger from a part-used cartridge without sucking a load of air in through the nozzle. Does the piston have a release valve or somesuch which can be opened when you want to withdraw it without bringing the cartridge's own own piston with it, or when you want to re-fit it to a part-used cartridge?
Very droll! But not such a big draw-back as an elephant's foreskin!
I've not tried the frameless one, but I can say if you've got any significant amount of cartridge use to do, I can really recommened a proper quality gun (=A320-25 iirc). The control and ease of use is just incomparable to the under =A35 stuff. A decent gun weighs a lot more, but still the 'difficulty' of using it is much less. I forget where I bought it though, so bit hard to recmomende the specific model :(
NT
I bought a new air cartridge gun from ebay for about a tenner and if you're doing of lot of sealing or using stiff stuff then I can't recommend them enough. Perfectly even application. Yes you need an air supply.
I have to say ~ "I don't work, nor receive any remuneration, from the manufacturer or distributor!" :) The principle seems to be thus ;- A cartridge of goo ( caulk, filler, pva ... whatever) consists of a plastic tube with a nozzle shape at the end. The tube is filled with the goo and closed with a movable 'piston' end. This piston is a dish-shaped circle that has backward pointing 'ends' ;
[_____]goo in tube
\ /
nozzle
Now, AIUI, the normal 'frame' type of device merely applies force to the piston cap and forces the goo forward. If pressure is relieved from the plunger ~ that's it: the no more pressure being applied but the piston cap still has a pressure and goo dribbles out of the nozzle. The type that we've been referring to is somewhat different; it's plunger end actually expands (two opposing dish 'washers' squeezing a rubber O-ring. This plunger end expansion actually grips the sides of the cartridge's 'piston cap'; thus when one relieves the pressure on the plunger it is possible to withdraw the cartridge's piston with the gripping plunger-end. The 'gripping' is achieved by rotating the plunger - using the ninety-degree bend part
[This is easy to demonstrate in two ticks, but seems to take yonks to describe] This rear-wards motion of the plunger cause a slight drop in pressure at the nozzle end and the goo is 'sucked back' a millimetre or two. Actually; this grip-the-piston's-sides facility is much more important than the frameless aspect of the device.The -normal- frame type only pushes the cartridge's piston cap and doesn't _pull_ it rearwards. When the cartridge is exhausted the piston cap is pushed right to the nozzle end of the cartridge - and you've now got to dispose of it - paying attention to the strictures about re-cycling ... but No! Not that ... !
As you've mentioned; when the cartridge's content has been exhausted with the frameless type ; you use the 'withdrawing mechanism' all the way to the end - plunger at full length: the piston will be seen to be gripped by the plunger-end. Unlocking the ring clamp mechanism enables one to pull off the nozzle-cum-tube (which as you've suggested is now 'full' of air - ready to accept a sausage of goo.
If one is using two types of goo - from two cartridges- then one 'leaves' the piston where it is and rotates the plunger bent-bit until one 'feels' it release its grip; then retract the plunger, swap cartridges, push forward the plunger until it touches the piston;rotate the end until you feel the grip action ~ then extrude goo to your heart's content. Once again [This is easy to demonstrate in two ticks, but seems to take yonks to describe]
I hope you my response has answered your questions.
Why not try QVC ; AIUI, thirty days to try it; if you don't like it send it back; you'll only lose the post&packing (both ways).
Sounds to me like a solution to a problem that doesn't exist
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