Semi Auto fail!!

Gun Freak · Sat Aug 13, 2011 1:20 pm

The volume of the cylinder is small though, the restriction is not enough to keep it from retracting, the restriction could only slow down retraction not prevent it.

django · Sat Aug 13, 2011 10:09 pm

Gun Freak wrote:The volume of the cylinder is small though, the restriction is not enough to keep it from retracting, the restriction could only slow down retraction not prevent it.

If thats the case then Im beaten as I have no other idea's or how to get it to work?, could the fact Im using my 20 oz co2 bottle to power it have anything to do with it ie denser than Air.

Crna Legija · Sun Aug 14, 2011 3:05 am

I don't think the restriction is the problem because i have a bigger air cylinder on my gun and its connected by 1mm id push to connect fittings.

if you can get a cheap slide valve off eBay to test if the 3way's at fault.

django · Fri Aug 19, 2011 5:05 am

Im now even more pissed of!!!, I got impatient and bought a new MVJO-3 Poppet Valve at $34.00 Australian

I screwed it onto the Cylinder and it does the same thing again!?.

I connect the air,rod extends out and hold's outwards with plenty of force,push the button on the Poppet then the rod retracts inwards and stays there,I then let go of the button and the rod extends out again?.

I asked at the Pnuematic shop and they were baffled too and suggested that there must be something wrong with the poppet Valve? so I buy a new one and its still the same. It MUST be something to do with that cylinder so I dont know what to do now.

That Aluminium block was a real damn pain in the ass to get all drilled threaded precisely and is dimensioned to that 40mm throw on the cylinder,cylinder's length and threaded ends, what a piss off....

Fri Aug 19, 2011 5:20 am

I connect the air,rod extends out and hold's outwards with plenty of force,push the button on the Poppet then the rod retracts inwards and stays there,I then let go of the button and the rod extends out again?.

Maybe i'm missing something but...

You connect the air and because the valve is normally open the rod extends out as the chamber fills. You close the valve, which vents the QEV, empties the chamber and the rod retracts. You let go of the poppet which opens the valve and fills the chamber with air and extends the rod.

That's how a 3-way valve should work. Maybe there's a misunderstanding or I didn't read something right...

django · Fri Aug 19, 2011 6:35 am

Well from my understanding and going by other members guns using the same/similar set up what should be happening is this=

1)Connect the air.
2)The Cylinder Rod extends outwards.
3)you push the button on the poppet Valve.
4)The Qev Valve Fires and Cylinder rod now retracts back quickly then flies forwards super fast and stays forwards until you push the button again.

Note: The Qev Fires and the cylinder's rod cycles once at the very same time,they work simutaniously

This was my understanding of it all anyways, POLAND WHERE ART THOU!

Whats happening with me is the Qev fires when the Rod is extended so the BB cant drop into the camber thus is doesnt fire it out

Labtecpower · Fri Aug 19, 2011 7:30 am

isn't that how it should work?

Connect air, rod pushes BB into the barrel.

You pull the "trigger", QEV pilots, firing the BB. Piston rod retracts, drops new BB into the barrel, you let go of the trigger, rod pushes BB into the barrel, etc.

Not to scale! forgive my poor paint skills.

Fri Aug 19, 2011 7:37 am

4)The Qev Valve Fires and Cylinder rod now retracts back quickly then flies forwards super fast and stays forwards until you push the button again.

Okay to be clear on this, which of these following two sentences best describes step 4 above?

a) The QEV fires and cylinder rod retracts when push button is depressed. Push button is released, air flows in to the chamber and the cylinder rod flies forward.

b) The QEV fires and cylinder rod retracts when push button is depressed but flies forward again while the button is still depressed.

As labtecpower has stated, it should work like sentence a. A video would really help

django · Fri Aug 19, 2011 8:22 am

Well it works as per stated in sentence A.

I thought it was supose to work per sentence B, seems I am wrong in how this design works!

.

I now have another problem,I made the Aluiminium block so that when the cylinder is pressurised the Cylinders Rod ends where the Qev inlet hole into the block starts.

So the Rod does not cover the air in hole at all,I did this to maximise flow but the damn bbs are dopping in the air inlet so causing problems so I have to fix this somehow?.Im hopeless sometimes

Labtecpower · Fri Aug 19, 2011 8:42 am

Maybe you can put a small piece of thin steel wire over the inlet, so the BB's don't drop in it.
I would put a small piece of iron on the piston rod, just long enough to push the BB over the air inlet.

Crna Legija · Fri Aug 19, 2011 8:55 am

django wrote:Well it works as per stated in sentence A.

I thought it was supose to work per sentence B, seems I am wrong in how this design works! .

I now have another problem,I made the Aluiminium block so that when the cylinder is pressurised the Cylinders Rod ends where the Qev inlet hole into the block starts.

So the Rod does not cover the air in hole at all,I did this to maximise flow but the damn bbs are dopping in the air inlet so causing problems so I have to fix this somehow?.Im hopeless sometimes

If you can fill the hole with melted lead or epoxy then re-drill and tap it a bit smaller than the bb

django · Sat Aug 20, 2011 3:04 am

I got the gun working but not 100%

I put two rare earth magnets upfront of the Aluminium block to stop bbs rolling into the air inlet and to stop them rolling out the barrel.

But sometimes it doesnt feed/fire the round out?,I havent made a mag yet either so holding a rag over the bb inlet hole,..LOL!.

Because I dont have a small seal/piston on the end of the cylinder rod the air is being wasted by flowing backwards up the BB Inlet,I cant put a seal on the rod cause its a bit out of alignment with the central hole in the aluminium block( Block's thread must be crooked )so will have to live with it I guess?.

Bit more tweeking hopefully it will feed right?,I wanted to make a bent mag so it lies horizontal but will be difficult as I'll need stronger tube than thin brass hobby tube because it'll be getting full psi through it due to the no piston on cylinder rod.

POLAND_SPUD · Sat Aug 20, 2011 4:16 am

This was my understanding of it all anyways, POLAND WHERE ART THOU!

Well it works as per stated in sentence A.

ohh so it was acctually OK but you got it in the wrong way? Damn

Because I dont have a small seal/piston on the end of the cylinder rod the air is being wasted by flowing backwards up the BB Inlet,I cant put a seal on the rod cause its a bit out of alignment with the central hole in the aluminium block( Block's thread must be crooked )so will have to live with it I guess?.

that's a waste
Can't you put a rubber washer sandwiched between two washers on the theaded rod of the cylinder ?

it doesn't have to seal perfectly as the pressure drops in a split second just stop 99% of air

or you can machine a new block

django · Sat Aug 20, 2011 5:13 am

I really dont want to make another block, it pissed me off trying to get it all right on this one,I want to put a seal on the rod but I think its too far out of whack mate.

I dont think the rod will retract if I try put a seal on it because it will touch on the side of the central hole material,if the spring in the cylinder was stronger I could get away with it. I'm still going to have a fiddle though and see if I can get something on there to help stop the blowback of air.

django · Sun Aug 21, 2011 4:30 am

ive spent all day working on this again,Ive=
1)Filled the Air Inlet with Steel Putty and re-drilled it at 5.5mm.

2)Made a Rubber Piston for the Cylinder rod,this has taken hours to file down the nut/ washer/rod/rubber so it doesnt jam. best I could do was the central block hole is 7.30mm or so,the piston at 6.5mm any more and it jams even with silicon oil ,still loses air rearwards but nowhere near as much!.

3)Smoothed the Chamber with steel putty and Crowned the barrel's inlet for a smoother transition for the bb 8) .

Test firing later today....

EDIT: I swear Im cursed

I was tightening it all back up again and that small brass fitting that screws into the back of the Cylinder broke off inside it,the broken threaded part is really small dia and no idea how im going to get it out!?.It loctited in with the weaker Blue Loctite,that fitting was for an airbrush and will have to be ordered in again ,the cylinder cost me $40.00 sohoping a tiny Easy Out or such will remove the broken part?