PCP building blog

[Gun Freak]

Alright thanks for the advice I'll try a 60 psi feed for filling up my scuba tank

[wyz2285]

Just finished the hammer and trigger
Here are some photos of the trigger
(Have next month full of tests and exams, so I won´t be able to do more progress until april )

[Cosmic Muffin]

What have you made the trigger and sear from?

[jackssmirkingrevenge]

What have you made the trigger and sear from?

Judging by the colour and consistency, this is my theory:

[youtube][/youtube]

[wyz2285]

nylon. They are strong enough and easy to work with.

[Cosmic Muffin]

Hahaha that's so bizarre Jack. Which show is that from? I'm familiar with him in Peepshow. That's such a great show. I'm thinking of making a trigger and sear from Perspex. Is that anywhere near as strong as nylon?

[wyz2285]

Only whatched the video now... :puke:
I don´t know much about Perspex, but the nylon I use is pretty strong.

[wyz2285]

Sorry for double post.
I made this counter-balanced hammer valve design, with parts I can make/find.
The seal/counter piston has the same OD, witch means there is no area for the pressure to working on, only the spring to keep the valve closed(witch means I need a weak hammer, and possibility for semi/full).
But, will it "dump"? I think no because there is the spring to push the stem.
The seal/counter piston has a OD of 10mm, at 50 bar it would be very powerful .
I don´t see any problem about this design, but before I start making it I´d like to hear your guys opinion.

[the unit]

Once it opens it will drain all the pressure in the firing and reserve chambers until it is equal to the force of the spring.

[wyz2285]

You sure? There is still area of the sealing, with a weak hammer it shouldn´t let all the air out, but it is a problem, as the valve doesn´t work as a regulator anymore witch means huge power at high pressure and low power at low pressure, as the valve opening time is the same...I will need a ajustable striker.

[Goats spudz]

a piece of metal got inside my fridgy a piece of file snapped while i was filing the edge it got in the secondary input where the oil goes, its not going to explode and kill me if i try fill my pcp is it? (ran it for 5 Mins no problem)

[Crna Legija]

what in gods name made you post that here?

[Gippeto]

Going to agree with the unit...as drawn it'll dump.

Wouldn't use an o-ring to seal on the striker side of the spool either...the pressure will get under it at the instant it is free to do so, and blow it right out of it's groove. Could cage the o-ring (see techs qdv for an example of caged o-rings), but that won't stop it from "puffing" up and rubbing/slicing on the opening/cage...o-ring life will be affected.

Would be better to use a partially balanced spool, and use the larger end of the spool to seal. This'll take care of the dumping problem and the o-ring issue. Look up BTB's "push button valve" if you're unsure what a partially balanced spool is.

You actually WANT the valve to close sharply to get a short blast of air behind the projectile...too much dwell time, and the valve is still open after the projectile has left the barrel. YES...maximum power will be achieved, but at the cost of using WAY more air than needed.


I see you're also planning to use screws in shear, so....here's a little bonus reading material for ya. Shear strength is typically 60% of Tensile strength (I use Yield)...if you cannot find compressive strength of a material, use the yield strength when calculating bearing stress. I use a minimum safety factor of 3 at yield.


http://courses.washington.edu/mengr356/ ... -joint.pdf

[wyz2285]

Thanks Gippeto
Ok I will try to fix the valve... But I don't know if I can find a new seal.
No I won't use screws in shear, not strong enough, they will have to deal with 200kg.

[Gippeto]

Screws in shear is an EASY design to calculate...used by many folks...myself included. I posted that link for a reason.

Plenty strong if done "right".