qev proplems ! ANSWER FOUND

[bravootome]

i am working on another qev fully machined so i avoid all those problems i had before, i mean a perfect piston in a perfect body. it is a multishoot.
this time the problem is that when i press to shoot that bang is not there, is only a fsssss, the bang comes at higher pressures over 10 bar( but still not that clear bang ). this fssss makes the gun very low power and performance. slower i press the pilot, bigger the fssss is. i made the piston area pretty large for the 6 mm gun, in order to decompress really easy. on previos tests i just had to touch a little the pilot's trigger and the piston responded prompt---- bang !
if you had this problem how you fixed it ? i use as a pilot the pilot from another working gun........
ANSWER : all those troubles comes from the wrong idea that bigger the diameter of the piston, faster and easier it would open, well not. Is a matter of physics. smaller it is, faster and easier it opens(since it press against 6mm pipe with lowerr power), with only few air piloted. So today i made a 10.5 mm piston(and housing) ( the previous piston had 21 mm.)for a sealing surface of 7-8 mm and i was right, now, it opens extremely easy and fast, but i will have to decreases pilot's volume( or to remake the piston larger, like 12-13 mm). but also the problem is that it pretty hard for this piston to seal the surface, no matter what i tried( only a hard spring does it).
i forgot to mention that the piston must open few mm by restricting him to travel more.

[wyz2285]

photos? I'm not sure if your piston is too tight (so only high pressure moves the piston).
Obviously slower you open the pilot, slower the piston opening (on a non-airtight piston)

[jackssmirkingrevenge]

http://www.ebay.com/itm/CHLED-1-2-Inlet ... 27d9da6bab

[bravootome]

photos? I'm not sure if your piston is too tight (so only high pressure moves the piston).
Obviously slower you open the pilot, slower the piston opening (on a non-airtight piston)

no, it not tight. at my other gun, doesnt matter how fast i push the pilot, it works the same,a good bang.
i notice the too much air is loosed from pilot just for a small decompresion of the piston. if i correct the semiauto spring like it should be( softer) the piston doesn't open at all. i tried i tighter/smaller piston but i got same thing.
instead of 30 shoots per one fill i got 15 very low power shoots.

[bravootome]

http://www.ebay.com/itm/CHLED-1-2-Inlet ... 27d9da6bab

i got same thing back here but without o-rings. machined.

[bravootome]

photos? I'm not sure if your piston is too tight (so only high pressure moves the piston).
Obviously slower you open the pilot, slower the piston opening (on a non-airtight piston)

[s0ka]

Hi, you should use a qev with check valve in it, like that:

[jackssmirkingrevenge]

How is the piston sealing face attached?

Also, you don't need the spring.

[dart guy]

soka, a floated and noched o ring would be just as good

[bravootome]

How is the piston sealing face attached?

Also, you don't need the spring.

I USED SUPERGLUE, the spring is needed when you inflate with air, or the piston is pushed back an air exits the barrel.

soka, a floated and noched o ring would be just as good

if i use o-ring i wouldn't get semiauto with what i have already made.

Hi, you should use a qev with check valve in it, like that:

and what for is the check valve for? i suspect when piston gets back the valve allow semiauto. but you wont get equal fires on different pressure this way ! cuz it allows semiauto only when the piston has travelled a distance back. different pressures = different piston speeds and distance to move.

[s0ka]

Hi the check valve is just to prevent any leack of the chamber to the pilot, and it could be as effective as an industrial QEV. When you whrited a perfect QEV i see that design!

[bravootome]

When you whrited a perfect QEV i see that design!

i meant, that will work perfect.

[oneocim]

I’m not quite sure with your multi shoots gun design but I assume since it need a spring behind its piston, it is a chamber filled or at least all the air for the second and next shoot is kept in the chamber and not the pilot filled that usualy use two way or sliding valve for piloting (if this is a wrong assumption you can just ignore my post). All my guns are in this design (except mine are pvc and use lower pressure). Based on my experience, when I got fssss, most cases were caused by my pilot valve. The pilot valve is not big or quick enough to decompress the pilot area. I solve the problem by making the valve bigger or the hammer stronger (I use hammer valve for piloting). I know that you use a pilot valve from other gun that is working but is it the gun with the same piston size or pilot area or spring strength?
The other causes are that the piston is to lose and let too many air flowing from the chamber to the pilot area or/and the spring is to strong. However, for these causes I have my own consideration, that when the piston is too tight or/and the spring is too weak, it let the piston open too long (and sometime just keep open until all the air in the chamber gone) so I chose to have too lose piston and to strong spring then the opposite.
I do have some question for you. What do you use for piloting the valve? Is it pop up valve that pressed manually? If so how you control the consistency of each shoot, since it should be different for long or short press. And the last one, for multi shoots with 6 mm barrel, why you choose piston valve rather than just a hammer valve?

[bravootome]

AS a pilot, i made a sort of a push of a buton valve, i control the consistency but not for eachshoot,, cuz it self regulated by a 3rd valve that makes this auto regulation. i control only the power of shoots by a spring inside the 3rd valve. there is a diagram of my pilot in my previos post.
i choose qev cuz i is a lot more powerfull( i also got a 6 mm hammervalve) and most of the shoots have same consistency and you dont have to load a hammer for each shoot, you just fire. i also made 2 years ago a 8 mm multishoot qev that works perfectly even today after at least 20-30.000 shoots. But damn if i know how i made it that good. i made this 6 mm one with almost same parts.

[bravootome]

how do you see the piston diameter in relation with the sealing surface diameter in order to a good decompresion.