Help with piston in coaxial QEV (never encountered this b4)

[DaxSF]

Hi,

Apparently I have a problem with my QEV. The piston I tried making out of epoxy didn't work out too well for some reason, so I stuck to my good old pal, the hot glue. I had a coax QEV on one of my airguns before, but because I haven't used it for a long time it got messed up so I decided to make a new one.

The problem is the following: Sometimes all the air will go through the pistol valve (the trigger), and sometimes the piston will go back only after the pressure has dropped down to about 20 PSI (after about 80 PSI went through the trigger *facepalm*). About 25% of the times, the piston will go back VERY slowly, while making a wiggly sound (like the piston is wiggling inside), after the pressure had dropped down to 30~40 PSI (from 100).

The piston itself has been tested without any slotting (didn't work almost at all), so I slotted it once (got better, but still almost no functionality), then slotted it twice (at least now it's going back lol). I'm afraid to slot it again.

See pictures below please!

P.S: I have been trying WD-40, Vaseline and olive oil as lubricant, same results with each one.

**Note: It is ugly because I haven't down any finishing to it yet.

Pictures:





Thanks in advance! [/u]

[jackssmirkingrevenge]

Could you draw a rough diagram of exactly how the parts come together internally? I have a feeling it's not the piston that's your problem, rather the configuration.

[DaxSF]

This is an exact copy of a previous configuration I had which worked amazingly. Here is the diagram:



URL: http://i50.tinypic.com/2e51jcw.gif

Thank you very much for the reply

[jackssmirkingrevenge]

You have a bit of extra pilot space but it shouldn't cause the problems you're reporting. What about the tube the piston rides in, is it smooth and perfectly cylindrical? Also, how much can the piston move?

[DaxSF]

I have 3 different pistons, an epoxy one which slides really smoothly but also isn't snug enough to stay in place, 2 hot glue ones (one I showed) which has medium place to move and another one which barely has any space to move back and forth. The tube itself is extremely smooth and lubed.

Thank you once again!

P.S: If you use Skype I'd be happy to show you via webcam anything you like.
Thank you very much.

[mattyzip77]

Try lubing the piston..... Otherwise to me it sounds like that trigger is defective....

[jackssmirkingrevenge]

Tell you what, if you can give me the exact diameter of the piston tube I'll machine a delrin piston for $5 posted.

[DaxSF]

Tell you what, if you can give me the exact diameter of the piston tube I'll machine a delrin piston for $5 posted.

That'd be AWESOME!
The inner diameter of the tube is 1.5cm (150mm), let me know how much that'd cost
Thanks!

[jackssmirkingrevenge]

As I said, $5 including postage. You need to give me an exact diameter though, measured with one of these, otherwise I cannot guarantee a good fit which is all-important for pistons.

[MRR]

So you lubricated the hot glue piston with WD40? I had bad experiences with it, over time the piston became sticky and soft, to a point that I had to remove it with a dowel and a hammer.

[DaxSF]

So you lubricated the hot glue piston with WD40? I had bad experiences with it, over time the piston became sticky and soft, to a point that I had to remove it with a dowel and a hammer.

It's a mixture of oils inside right now, lol.
Do you have any suggestions? For the time being, it works fine-

I know I am going to have problems in the future because that's how my previous gun broke. I didn't make the piston serviceable.

[Zeus]

Can I add, WD40 isn't a lubricant, it's a water dispersing oenetrant. Silicone/moly grease is some of the best lubricants for pistons, as is Vaseline. I use a fairly thin bearing grease with moly, so I have great results.

As MRR said, WD40 can dissolve hot glue, and it ends up quite tacky after a day or so. It can swell too, but I haven't seen it before.

Jack, I might employ your services soon. I'll get a sketch together.

[jackssmirkingrevenge]

Here you go

Jack, I might employ your services soon. I'll get a sketch together.

Will be away from my tools for February so if you need something urgent let me know asap.

[DaxSF]

Here you go

Jack, I might employ your services soon. I'll get a sketch together.

Will be away from my tools for February so if you need something urgent let me know asap.

If that's mine, looks really good! I'll PM you my address.

[jsefcik]

Hes has two of my valves making pistons for em:)