Need info.............

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DoctorFrankengun · #1 Post by **DoctorFrankengun** » Fri Jan 20, 2006 6:26 pm

I have just read an artical in Aigun Hobby magazine about the Theoben "Evolution" air rifle. The Evolution apparently has a "gas ram" system instead of a "spring ram".

Does anyone know how the "gas ram" works? Or, does anyone have an exploded diagram that shows the parts that make up the "gas ram"?

350mag1 · #2 Post by **350mag1** » Fri Jan 20, 2006 6:42 pm

The operation is like that of a strut that you would see hold a rear door of a van or such. The rod compresses the gas in the unit. When the trigger is pulled, the rod shoots forward. I like the advantage of being able to pre-set the power level of the unit and that you can keep it cocked and it will not affect it. The only thing that makes me wonder is if it would leak after a while and the cost of replacement. I remember Russ Best mentioning this before.

#3 Post by **sniper** » Fri Jan 20, 2006 6:49 pm

The way I see it, it's like break barrel cocking using power like pcp.
pump it from behind.
one example is the HW90:
Schematic diagram:
http://www.twcguns.co.uk/Weihrauch%20pl ... 20plan.htm

Tailgunner · #4 Post by **Tailgunner** » Fri Jan 20, 2006 7:07 pm

Then really, all that is taking place is that a mechanical (spring) stored power source is being replaced by compressed air. Makes sense to me and apparentely works quite well (from the little I've read on Theobens). The concept of pushing a piston back into an enclosed chamber will compress the air in the chamber.........then, when the piston is released, it will cause a compression of air IN FRONT of the piston........thus driving compressed air into the chamber of the barrel.

Problem here is that there is no way to 'MOD' this system without introducing high pressure air into the compression chamber from a remote source (HPA). So, why not just use HPA in the first place through a valving system and forget about the initail compression system.

OR......I haven't really grasped the concept.

VOLTAR........are you out there???? Can you help us out on this????

Cheers - Gus

350mag1 · #5 Post by **350mag1** » Fri Jan 20, 2006 8:14 pm

A picture of the Theoben gas strut
http://www.airgun.org/vulcan/types.htm# ... 0Gas%20Ram
PCP's are different altogether.

ustilago · #6 Post by **ustilago** » Fri Jan 20, 2006 8:41 pm

rennugliat, you've answered your own question. It's not a modable system. It's for people that don't want to get their hands dirty.

Drop in a gas ram and forget about it. No more spring recoil, no more tearing down and relubing springs, no more replacing springs.

Just break barrel, load and shoot. Repeat as necessary.

Although, for the price of a gas ram (just the ram) I could buy several crosman pellet guns. (115.50 british pounds + shipping that's what? $200-250 CDN)
available as 12 or 18-21 ftlb units

*edit* I checked the prices on some of the other models. 66.95 British pounds, still a little pricey for an upgrade if you ask me (like that ever happens). */edit*

Mulby · #7 Post by **Mulby** » Fri Jan 20, 2006 8:46 pm

The gas strut system works on the exact same principal as a regular spring powered piston gun. The strut always has pressure in it just like the preload on a mainspring, and can be charged to different levels depending on how much power you need. When you cock the rifle it simply further compresses the air in the strut. A full charge on the HW90 ram is max 26 bar, and out of the box and after a few hundred rounds mine was doing high 800's with 10.6gr Baracudas. I let pressure out of the ram until the rifle averaged 905fps with 8.44gr JSB Exacts 4.52mm, I find the rifle the most efficient at this power level with a reasonalble cocking effort and best accuracy from my unscientific testing.
One benifet to the ram system is the snappy, vibration and torque free shot cycle which helps with shooting the gun accurately. Another and my personal favorite is the ability to change energy levels by letting air out of the strut or pumping more in to bring it back up.
I havn't taken my 90 apart yet, but I'm assuming that changing seals throughout the gun is as simple as discharging the air from the strut and removing the ram and piston from the reciever then reassembling and recharging with new seals installed.
If I ever have to do any repair to my HW90 I'll know for sure how it goes, but until then I ain't fixin' what ain't broke. It shoots great at 15.4fpe, very accurate & consistent with the JSB pellets. HTH

Mulby

DoctorFrankengun · Fri Jan 20, 2006 10:32 pm

Thanks for all the info fellows. In the schematic that sniper posted it looks just like a regular air cylinder.

Mulby, how do you add air to the cylinder? What kind of fitting is used?

Mulby · #9 Post by **Mulby** » Fri Jan 20, 2006 11:18 pm

For the HW90 there is a specific hand pump, hose, and gauge for the strut. The end of the hose that attaches to the strut has a male type brass fitting that threads into the valve at the rear of the reciever(behind a screw that must be removed), then the opposite end of the hose is threaded onto the male brass fitting on the pump. When you pump, the pressure built up forces the valve open allowing air in, letting air out is as simple as depressing the valve stem which opens the valve.

In a sense, gasram airguns are like "pneumatic" piston guns.

Mulby

DoctorFrankengun · Sat Jan 21, 2006 9:22 am

Mulby wrote:For the HW90 there is a specific hand pump, hose, and gauge for the strut. The end of the hose that attaches to the strut has a male type brass fitting that threads into the valve at the rear of the reciever(behind a screw that must be removed), then the opposite end of the hose is threaded onto the male brass fitting on the pump. When you pump, the pressure built up forces the valve open allowing air in, letting air out is as simple as depressing the valve stem which opens the valve.

In a sense, gasram airguns are like "pneumatic" piston guns.

Mulby

Thanks, I think I get the idea.