Springs are at the heart of airguns. The drive the hammer in gas guns, they drive the piston in springers. Lets ignore springers for a while and focus on gas guns.

Gary's post elsewhere talks about the concepts of Pneumatics. hammer spring knocks open the valve, gas escapes, reservoiur pressure pushes it shut. Every gas gun valve Ive erver seen or seen pics of has a return spring. Why?

If the reserviour pressure is great enough, it will eventually push the valve shut. But now it seems you are stuck with the latency inherent in the design. Maybe thats good, or good enough. What happens though when you change pellet weights? or you need to get consistant velocity or more consistent gas usage (oh no, the dreaded "shots per fill" )

Gary has said on many occasions, that the airgun is a system. Change one aspect of it, the other try to adapt to the change. I can attest, first hand that he is absolutly correct.So can this change be managed or harnessed?

If you have a heavier hammer spring, and a stock valve return spring, is that a better setup than a stock hammer spring and lighter (than stock) VRS? Ah, now we are entering the land of Vood doo....

What performance changes would a heavy hammer and heavy VRS give? or both springs lighter?

Other than extensive experimentation, do you think its possible to apply some generalities to making changes to spring power? (other than reading the ground in the bottom of the coffee cup). Or are the various implementations too varied to make that kind of general prediction?

The valve return spring, holds the valve shut (when the reservoir is empty) in order for you to start your fill. In a "knock open valve system" (which are 95% of the PCP guns you will ever see) .... it does nothing else.

In antique guns, which often used valves that "flipped" a valve lever, and then disengaged (meaning the hammer and hammer spring did not continue to lay against the valve stem) .... in those "flip open": systems, the valve spring "MIGHT" have had a "MINOR" role in closing the valve. It's there, in modern designs, to hold the valve head closed during filling of an empty gun.

The residual pressure inside the reservoir, is what closes the valve. That's a huge force. It acts to try to "expel" the cork like "valve head" from the reservoir chamber. But; the valve head is too big to get out thru the valve port ... and thus - it sticks in the valve seat (sealing the reservoir).

In our guns, there's no reason to change out a valve return spring. It won't do a thing for you - other than waste your time.

Gary

Whoa! years of airgun theory right out the window in a couple of sentences.... hehe

Ok, I'll admit to be a little set back..... so really any performance change will come from changing the hammer spring? Knock it open longer, or not as long.

Assuming we get consistent dwell time on the hammer and valve, we would be better off looking else where for gains or consistentcy?

It occurs to me that we may be creeping up on how self regulation works....

I'd say you're more "stomping" up on valve regulation, hammer system tuning, and a few rooms full of things behind doors 5-9. hehe.

Gary

"Assuming we get a consistent dwell time on the hammer and valve" ..... ????? That's what you are working to achieve AFTER about a week of tuning.

Wanted to clarify my thought, to all readers.

Bringing your rifle, to the best of it's engineered performance, is the best you can do. And, it's going to be small things that you can do better than the engineers which designed the product to begin with, or the craftsmen who built it. Recall my many discussions about "hot rodding" guns. Just because you can get into an area ... doesn't mean that you have the background, or skill set, to change things ... that just might happen to make the gun unsafe.

PCP guns are quite complex. A small change, can raise breech pressure far above what the gun was designed to handle. Of course, never overfill a gun. One of the things I always saw and read about, was somebody overfilling the gun, and then finding a way to make it fire at the higher psi. Dangerous, and foolish.

A powerful PCP gun, is "engineered" to be powerful. It's not made from altering a low power gun. That's a sure way get hurt.

Best,

Gary

Soooo.....

now we are down to hammer weight and hammer spring strength? And that gets us into laws of inertia, and outside my comfort zone....

Very interesting discussion Gary!

Hello Dan,

There are quite a few more things that go into "tuning" (without hot rodding): A few examples are ...

1. Friction (fit of hammer to hammer tube, hammer to trigger sear, hammer to main spring)
2. Friction (lube on hammer, hammer tube, main spring, and spring guides)
3. Friction (finish on hammer and hammer tube, guides, cavities)
4. Friction (spring guides ... design type, material, fit and finish)
5. Trigger design (overall design, sear type, sear release, sear angles, spring loads)
6. Sear drag (on trigger components, on hammer body)
7. Hammer travel (total travel, free travel)
8. Recoil of hammer (pre-loads, balance between valve and hammer system)
9. Spring composition (size, material, design)
10. Wear and tear on components (compatible hardness of moving parts)
11. Adjustable components (balance)
12. Mounting methods of components (pinching, galling, protruding machine screws, burrs, tightness, stripped taps)
13. Pivot pins (size, material, fit, wear)

And many more ....

Gary

So Dan,

Have you figured out that everything is a compromise yet?

There are a couple rifles out there that might possibly respond to return spring changes but that is only because they are tuned to a power level that matches what the ports can handle or they have a "pre-chamber" and closing the valve a bit faster can save some air. The point I'd like to make is that some questions might be particular to a particular design and the answers will only be accurate in that context. I don't think it would be a fair question to ask about some specific geometry or configuration in a "101" post if you were looking to unveil a tuning secret for a particular gun....

Jerry Wrote:
-------------------------------------------------------

> Have you figured out that everything is a
> compromise yet?
>

Oh yea, have known that for a long time, and get reminded in some not so subtle ways sometimes... like whacking a barrel down to 8 inches and wondering why the gun gets harsh.....

Gary's list above contains a lot of stuff that applicable to all airguns. Efficiencies can be gain across the entire "system", but each by themselves is an incremental improvement. Taken together though, they can change a good gun into a great one. What I think needs to be kept in mind, is that you cant push or pull the gun's design too far. Sure, adding a slightly heavier hammer spring will gain you something, but if you go overboard on it, you will have some adverse reaction elsewhere in the "system".

I think my lesson here is to not push too far past what the original designers had in mind. Back to Jerry's compromise, the designers and manufacturers of the guns also must make compromises to build and sell these things in a profitable way. So the things they cant do in a mass production environment, we can finish on the work bench. Is that fair?

That makes sense to me. I think a lot of guys get pleasure out of tinkering with their guns getting them to shoot smoother or be a bit more efficient or a little more powerful. It's all a nice hobby. Just so long as one doesn't go too far and do something dangerous.

Speaking of dangerous; I saw a post on another forum where a guy asked if anyone had tried pure oxygen in their PCP! Thank God he asked! I wonder how many times that has been done. I also wonder how anyone could make it through high school and even consider using oxygen. Do they teach chemistry these days?

Now helium might be a fun experiment....

Lol, helium would be funny! After a few shots from inside the battle wagon, you'd start to sound like a smurf!!!

THAT I would like to see on a 'Jerry Video'

Better finish the "why" of the warning. Oxygen is flammable. As in "BANG ... BIG FIRE". Airguns, working with very high psi, can cause combustion due to compression. Don't do it.

My understanding of Helium is that it's a very small molecule, therefore; it's much harder to seal. My understanding is that a gun that works fine with High Pressure Air (HPA), might leak like a screen door with Helium. Also ... PSI is PSI ... so don't every use anything flammable, and don't ever exceed the recommended manufacturer's psi.

Gary

Also; don't get the idea I'm militant about anyone tuning their guns. If you have the skill set, I'm not on a campaign to ruin your fun. My warnings are about trying to "beat the system" and "hot rod" some simple artifact into a dangerous mess. Nothing else.

I hope it's also obvious that I'm not the most unbiased person to speak to about "tuning". I've always committed myself to selling a complete, and refined product. That's why they take awhile, and cost a bit.

You know, in reality ... that bites me in the buttstock, quite often. Ya see; I've always thought that people would enjoy "shooting" the guns. Figuring out reactive targets, doing neat photography, refining bench shooting technique, exploring the optimum ammo, sharing their shooting outings. Rarely happens though. Seems as thought the accuracy of my rifles, their consistency, the fine triggers, and quality .... just ruins all the fun, and there's nothing left to do.

Gary

barnespneumatic Wrote:

> just ruins all the
> fun, and there's nothing left to do.

Um, except SHOOT IT!

Jerry Wrote:
-------------------------------------------------------
I don't think it would
> be a fair question to ask about some specific
> geometry or configuration in a "101" post if you
> were looking to unveil a tuning secret for a
> particular gun....

nothing in particular. Just trying to understand the (now non-existent) relationship between the hammer spring and valve return spring..and how that can be exploited to get either more shots (just dont say that around Gary hehe) or more power.

Having said that, here and other posts, that maybe its not about spring stoutness or valves, but of duration and the path the gas takes--how you open the valve is not as important as how long it is open and where it goes..... (hey, need a light bulb smiley...)

Yes, helium (never oxygen)... it's a light gas. You know those light gas guns....? [en.wikipedia.org]

Speed of sound is much higher in helium, and thus it should be possible to reach enormous speeds with helium. There was some people who planned to use or apply helium to their PCP's. I haven't heard did they try anything after all.

I wouldn't put helium in my airgun though (and especially don't want that anybody else would put helium in their guns), because I don't know enough about it. Helium is inert noble gas I know, but how it acts under pressure, and how it affects the gun in high pressure... ?

Experiment should be done after full knowledge of the topic is acquired, carefully and cautiously in each case. Interesting thought experiment though that helium using...

I think its because helium expands alot faster than air, and therefore gives you more power per psi. Have heard of people doing it, though never heard any results. In theory it should be ok to do. Maybe because its expensive that its not more widely tried/used?
And yeah, compressing oxygen its a REALLY bad idea. I used to wear clean gloves when dealing with high pressure oxy units. Even grease from your hands getting onto an oring in high pressure oxygen equipment can make it go bang. You dont mess about with it.

I have a story about liquid oxygen.

This guy I knew was in the miltary long time ago, and they used LOX for some airplane oxygen supply. He told me this story.

They were always messing around with the stuff, freezing things in the over flow pans. One day they caught a rat int the tire shop and they threw it in the pan of LOX and froze it instantly. And then they picked it up by it's tail and flung against wall expecting it to fly into tiny little pieces. You probably guess what happened. It blew a big hole in the wall. Apparently it had been eating a lot of grease and stuff around the shop. And on impact it combined with LOX saturated rat. It was a lot funnier when he told it. Dory

So .. the moral of the story is ... the military NEEDS pneumatic cannons to shoot LOX rats!!!

It's sooooo obvious ....

Gary

C'mon now Gary, don't go giving them any ideas.

On a slightly more serious note, a couple of jobs ago I flew a civilian EMS helicopter that used a liquid oxygen dewar instead of high pressure bottled gas to supply medical O2. From a pilots perspective it was the cats meow, you only had to change it every three or four days instead of topping off the tanks every flight or two like you have to with bottled gas. The dewar was about basketball sized, held about eight litres liquid oxygen when it was full up. The expansion ratio for liquid to gas is about 860 to 1 with LOX so those eight-ish liters made a LOT of gaseous O2, you would never run it dry even on a busy day. Since it slowly boils off even with the excellent insulation provided by the vacuum layer, you'd have to change out tanks twice a week or so even if you didn't use it in flight so we always kept a spare one filled up near the helipad.

The upshot was that we saw the LOX supplier guy around quite regularly. He topped off the spare tank once a week and if we were low on the primary we'd switch so that we could get them both full, just in case we got busy. I used to go watch him fill the dewars at first but it soon gave me the creeps so I quit watching and just waited for the "boom'', which fortunately never came. I was always taught that too much oxygen was a dangerous thing, and to never get it near grease or oil...but...he always filled the dewars in the back of his panel truck, with a hose that had several pinhole leaks, right next to the greasy lift gate. Part of the filling process is to cool off the dewar as much as possible by venting a considerable amount of LOX through the overflow filling with a special fixture. It would fill half the ambulance bay with white fog, it just rolled out of his truck and poured over the greasy asphault parking lot. His hose leaked like a sieve, it would piss streams of LOX out right onto the truck box floor the whole time he was working, which would also evaporate into yet more white fog. The whole back of that truck had to be a highly concentrated oxygen environment, yet it was full of greasy machinery like the lift gate. His leather gloves looked like they'd been dipped in grease, his uniform was always greasy looking, and to top it off he was a chain-smoker. Somehow, he never went up like the torch that I always half expected, and I watched him do it the exact same way every week for five years...go figure. Was he just preternaturally lucky, or do you need a lot more concentrated O2 than we were seeing in those circumstances?

BTW, it's one of grim ironies of the medical business that every hospital of any size always has a sizable population of smokers, and a shockingly high percentage of them will always be respiratory techs. You know, the gals and guys that see lung cancer patients all-day every-day. And for whatever reason, the other group that always seems to have a lit cigarette in their hand is the fuel truck drivers. Nothing like a steady diet of hundred-octane and jet fuel on the uniform to make a man want to light up every chance he gets.

Hopefully that delivery man has not torched himself yet! There is of course the danger of a more intense fire in an oxygen rich environment but that danger is not as high as what is likely when you put the pure oxygen under high pressure. Under high pressure small amounts of flammable material can autoignite and then you've got a real mess on your hands. NASA has developed some standards that define how much contamination is safe in oxygen systems and it's not a lot! I read a study online that examined this in depth. They were able to verify the NASA standards and also show some other interesting stuff. One of the neat things they observed were flow induced pressure peaks where the piping had a constriction or change of direction there would be momentary surges in pressure in small spots.

Yeah, high pressure oxygen changes things a LOT. If you've ever seen an oxygen lance at work it's sorta scary. I don't think there's anything one of those won't cut through, and usually like the proverbial hot knife through butter. The concept is stone simple, just a hollow steel tube that's consumed by the high pressure O2 blasting through it, which when you think of it sounds a whole lot like someone trying to run an PCP airgun using an O2 tank!

Given my experience with aircraft, I'd much prefer to fly one that uses LOX instead of high pressure oxygen tanks. The conveinence factor is a big part of it, but I've actually seen a King Air turboprop totally destroyed by a ramp guy that was using improper technique to refill the O2 tanks. He tried to speed things up by just cranking open the fill cart to full pressure instead of gradually topping off the tanks. When one of the supply lines in the aircraft melted through due to the heat of sudden compression, the entire supply let loose through a 1/4" hole. The result was a ten-foot long jet of white-hot flame that cut through the aircraft fuselage like it was tissure paper, narrowly missing the wing fuel tanks and nearly burning down the entire hangar. The airport fire department only took about two minutes to get there and although the oxygen fire was long since out, they filled the smouldering interior with hundreds of gallons of foam anyway. That stuff is pretty corrosive, so they effectively finished off the aircraft fuselage and ruined all the avionics as well.

In comparison, the LOX system would vent at only about 200 PSI, so we never had to deal with the high-pressure issues. Of course, if the integrity of the LOX dewar had ever been breached it would have been pretty ugly, but those things are pretty tough.