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Discovery Rifle's Air Tube & Valve Assemblies Tested to 11,000psi hydrostatically! LINK

June 23 2009 at 3:09 PM
  (Login Trojan1994)
Crosman Forum Member
from IP address 67.170.202.238

 
With all this discussion of the Discovery and safety concerns, I found out through our Discovery Forum that Jim Chapman, world renowned as the American Airgun Hunter reviewed the Benjamin Discovery.

Apparently Jim Chapman was contact directly on his personal cell phone by the Project Manager for the Discovery Air Rifle that he was selected as a candidate to test the new rifle given that it would have a "major impact on airgun hunting."

In the review, link attached, he specifically noted that "Though the recommended fill pressure is 2000 psi, the tube and valve assemblies have been hydrostatic tested to 11000 psi (the tube alone to 15000 psi). "

http://www.americanairgunhunter.com/benji_discovery.html

A very informative, professional and entertaining article to say the least.

Regards,

Tony

 
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AuthorReply


(Login pneuguy)
Crosman Forum Member
68.221.11.159

As true as it is meaningless.

June 23 2009, 3:24 PM 

Meaningless because we don't shoot with air tubes and valve assemblies. We shoot with complete airguns, and nothing in Jim's article says anything about about pressures the complete gun was tested to.

The "tube" being tested separately is mentioned, and the "valve assemblies" being tested separately is mentioned. (If you're curious what the "valve assembly" is, look at "item 18" in the parts diagram.)

But nowhere is there mentioned anything whatsoever about a pressure test of the entire gun.

That's why I did the simple exercise in engineering math posted yesterday (verified by Bomont's testing) to show that that's where the Owner's Manual maximum fill pressure number of 2000psi came from - the pressure limitations of the complete gun.


Steve

Air Conserving MSP 392
GTX Generation II 2-Stage Trigger
Benjamin SuperSear
Crosman Custom Parts
Big Ed Airguns


    
This message has been edited by pneuguy from IP address 68.221.11.159 on Jun 23, 2009 3:26 PM


 
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(Login Trojan1994)
Crosman Forum Member
67.170.202.238

So you find Jim Chapman's information MEANINGLESS?

June 23 2009, 3:34 PM 

Didn't look like Bomont tested an entire gun...

Given that Jim and others worked directly with Crosman and that YOU DO NOT(unless you would like to clarify that), I will take heed of his printed words and fear not of slight over fills, say 100psi, in my Discoveries.

Cheers Steve! happy.gif

Regards,

Tony

 
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(Login jebudite)
Crosman Forum Member
74.44.184.235

Thanks Tony for all your effort to set us straight on

June 23 2009, 3:42 PM 

The PSI, I know you spent your time to help us out on allot of things and I hope you continue to do so, you always have been a POSITIVE A+ to Air Gunning and Air Gunners, Crosman never put out a PCP with out a large safety factor built in, thanks again Tony. Joe

 
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(Login Trojan1994)
Crosman Forum Member
67.170.202.238

You're welcome Joe and Thanks, I try to follow the examples set by other

June 23 2009, 3:50 PM 

fine airgunners and help where I can, share what I know and ask when I don't know if safety is involved.

Regards,

Tony

 
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(Login pneuguy)
Crosman Forum Member
68.221.11.159

Correct. What Bomont tested was the strength of a #8 valve anchor screw.

June 23 2009, 4:22 PM 

And this is what Jim said in the same Disco article you linked to about how the Discovery valve is anchored: "The new valve is anchored in place with three screws rather than the single anchor point used with the 2260."

Therefore, according to Bomont's test (and incidently my math) and Jim's article, the valve can be expected to blow out the back end of the tube at a pressure of approximately 6000psi. Maybe 6600.

But certainly not 11000.



Steve

Air Conserving MSP 392
GTX Generation II 2-Stage Trigger
Benjamin SuperSear
Crosman Custom Parts
Big Ed Airguns


    
This message has been edited by pneuguy from IP address 68.221.11.159 on Jun 23, 2009 4:33 PM


 
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(Login Trojan1994)
Crosman Forum Member
67.170.202.238

Well if you think you know more than Crosman and the information they provided Jim...

June 23 2009, 4:25 PM 

have fun with it. happy.gif

Regards,

Tony

 
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(Login pneuguy)
Crosman Forum Member
68.221.11.159

Nope. I think when Crosman says: "DO NOT fill the airgun to more than 2000 psi." they...

June 23 2009, 4:32 PM 

...know exactly what they're talking about. It's other "experts" who claim to know better than Crosman.

Steve

Air Conserving MSP 392
GTX Generation II 2-Stage Trigger
Benjamin SuperSear
Crosman Custom Parts
Big Ed Airguns

 
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(Login lhd)
Crosman Forum Member
75.104.109.8

Tony, I agree with you if you seem frustrated by what seems a deliberate attempt

June 23 2009, 4:41 PM 

At denigrating a fine writer's words and a good guy, devoted to airgunning. Chapman doesnt deserve that, juat as Josh didnt deserve some of the jibes thrown at him from the same source recently about a new entry.
As to the crack about "meaningless test", I'd like to point out that I disagree ... Crosman did right to select and test components separately first, then together, as a part of the design and evaluation segments of their project.


    
This message has been edited by lhd from IP address 75.104.109.8 on Jun 23, 2009 4:43 PM


 
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(Login Trojan1994)
Crosman Forum Member
67.170.202.238

Yes sir, I believe we are on the same page. Demeaning Jim's

June 23 2009, 5:06 PM 

work as a Professional Writer, Respected Airgunner and Hunter is truly sad and pathetic.

It is particularly disturbing that it is done with the sole intent to boost one's fragile ego, let alone as part of and indirect(cowardly) attempt to discredit and cause commercial frustration with an established business that has provided airguns and services for generations.

I wonder how long this will be tolerated. I presented fact from an independent 3rd Party that worked with Crosman, spoke with Crosman, and its ok to call this source and information meaningless? How much leeway is given?

Regards,

Tony

 
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Doug Owen
(Login DKOwen)
Crosman Forum Member
24.130.132.149

I gotta agree....cold shot.

June 23 2009, 5:52 PM 

I can't see accusing Jim of being deceptive in his writing. To what end? Why would he?

From the context he's clearly talking about the new pressure system. He didn't say 'the valve assemblies were tested to 11,000 psi and the tube to 15,000'. I read it as the assembly went to 11,000 and the tube alone was taken to 15,000. I think most folks do as well, I'm confident that's the impression Jim wanted to convey...and he's a top notch communicator.

I guess it's yet another example of not liking the message and going after the messenger?

In the end it's no big deal to me, the gun is VERY safe at 2000. Or 2100. Jim rightly called it "Though the recommended fill pressure is 2000 psi,...". 2000 psi is a compromise fill (to favor CO2 use on a gun without user hammer adjustments like the Marauder) and is a "recommended fill" not a "maximum" or "limit". If the burst strength of the system is 6000 psi (by calculation) or over 11,000 (by test) the pressures we're using these fine guns under seem safe enough to me. I'd have no problem charging my Discovery to 2100, but in my case the MV is already down about 10 fps from peak (around 1600 psi).

But then what do I know? Only what I read, see and am told I guess.

Doug Owen

 
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Ron
(Login oo7fuzz)
Crosman Forum Member
65.31.184.65

Three 8-32 would fail at 11000 psi test

June 23 2009, 5:40 PM 

Steve, I'm using your collective tensile strength for (3) 8-32 screws at 2700 pounds. Using that number, and allowing 75% of tensile strength rating to determine shear strength, which is generous, the collective shear strength of the three screws would be 2025 pounds.

Reservoir pressure on the valve with a 2000psi fill would be 833 pounds. So that factor of safety would be 2.43, No?

If so,Factors of safety are law and for pressure vessels that number is usually 3.5-4. But that may not hold for airguns.

So If one was to fill with a scuba tank which factor of safety is governed by strict code, then why would one fill a gun with less protection and hold it next to his good looks?

Is my math fuzzy? Check it out.

LD, on the other form stated that there are additional defences in case the screws would fail. Such as end plug, sear and bolt stud. But those should not be considered in factoring safety. But it is good that they are there.

 
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(Login pneuguy)
Crosman Forum Member
68.221.11.159

Of course your math, my math, and Bomont's test all predict failure long before 11,000psi.

June 23 2009, 5:54 PM 

But hasn't it become obvious that none of this is about airguns, engineering, physics, nor even reality?

Steve

Air Conserving MSP 392
GTX Generation II 2-Stage Trigger
Benjamin SuperSear
Crosman Custom Parts
Big Ed Airguns

 
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(Login arathol1)
Crosman Forum Member
205.188.116.144

funny how when you take words

June 23 2009, 5:44 PM 

out of context you can twist them to say just about anything.

"we don't shoot with air tubes and valve assemblies. We shoot with complete airguns"
Really? Every modular gun (2240, 2250, 2260 etc) sold by Crosman is just that, a base powerplant assembly design consisting of a tube and a valve, with various peripherals such as grips, stocks, barrels, breeches etc added to make different models. Since the Disco is an extension of the 2260, its no different. The peripherals have little effect on the operation of the powerplant whether its a pressure vessel or
CO2 cart tube, they are mostly cosmetic.


"The "tube" being tested separately is mentioned, and the "valve assemblies" being tested separately is mentioned"

Actually, here is the text you are referring to -

Though the recommended fill pressure is 2000 psi, the tube and valve assemblies have been hydrostatic tested to 11000 psi (the tube alone to 15000 psi).


Notice how it says that the assembly is tested separately from the tube itself to 11000 rather than the 15000 for the tube alone. This would indicate that the "tube and valve assemblies" tested are just that, assemblies consisting of a pressure tube and valve as found on a working gun.

[linked image]
[linked image]

 
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Ron
(Login oo7fuzz)
Crosman Forum Member
65.31.184.65

The challenge

June 23 2009, 5:55 PM 

Lets take the assembly you speak of. But instead of pressuring it up to 11000psi, lets only do 8000psi and even add a couple more 8-32's.

Would you hold your hands over either end durring the process?

Lets put your money where your mouth is ....or your hands were.

 
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(Login Trojan1994)
Crosman Forum Member
67.170.202.238

Considering few airgunners have the fill equipment to go past 4500psi

June 23 2009, 6:11 PM 

I think that would be a better test as a practical matter, i.e. someone cracks open the fill valve on their 4500psi tank and accidentally as a Disco to filled...

Regards,

Tony

 
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(Login richwoods)
Crosman Forum Member
68.7.204.116

I've been wondering...

June 23 2009, 9:15 PM 

..how much pressure the Walnut stock would take before it cracked....

 
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Ron
(Login oo7fuzz)
Crosman Forum Member
65.31.184.65

I can eat 50 eggs

June 23 2009, 10:12 PM 


 
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(Login randyfb)
Crosman Forum Member
216.252.78.1

as read, I don't see anything definative.

June 23 2009, 5:24 PM 

the ultimate answer is to destructively test a discovery reservoir.

install an aluminum endcap and a valve assembly and see exactly where the rubber hits the road. I have a feeling the endcap will be the failure point. the question will be what is burst pressure on the assembly, IMO, Bomont's shear test is pretty indicative of where burst will be.

we've been down this road so many times and we're still too cheap to do destructive testing and get a definative answer. I mean, how many threads have been started on the strengths of the 22xx tube? plenty, how many destructive tests? none that I've seen, some rumours but nobody has gone as far as Bomont in actually breaking pieces.

JMO,

fireball.gif

 
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Doug Owen
(Login DKOwen)
Crosman Forum Member
24.130.132.149

And a good opinion it is

June 23 2009, 6:04 PM 

There's lots of theory and lots of arm waving going on, few hard facts to deal with. I like the load the screw idea, but it too has some issues.

It's really too bad we can't take half the effort we waste here on the topic, convert it somehow to cash and just buy a Discovery and see. Hey, it's a $200 gun, even if we can't get just the parts we need cheaper. For myself I'd like to put a modest side bet on the pressure gauge. Maybe it fails first?

For myself I'm comfortable the maker did proper design and testing (whatever the details) to make a safe product, same as AF, AA, Theoben and the rest. I feel quite safe at 2000 psi or even 2100. In fact 3000 since that's what Hans and Ray are doing with the same gun action makes me feel the factory thinks 3000 is safe as well. If they were worried about guys pumping the gun up to the dangerous level I suspect they would have told us so in no uncertain terms. Something like "Caution, pumping to more than XXXX psi could damage your gun and cause serious injury". That sort of 'lawyer talk'. I think LD has it here, they don't see how your going to pump it high enough to get hurt.

Still I agree, it would be nice to stress test one to failure for the education....or at least the fun of doing it.

Doug Owen

 
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(Login pneuguy)
Crosman Forum Member
68.221.11.159

I think that's a pessimistic conclusion, Trevor. My take is: It's not so hard.

June 23 2009, 6:52 PM 

If you adopt a model of the pressure capacity of an airgun that's like the proverbial chain that's no weaker than its weakest link, then pressure capacity can be estimated by...

1. Looking for a weakest link.
2. Estimating its strength.

At the very worst, even if you don't find the weakest link, this method will set an upper bound on safe pressure based on the weakest one you do find.

Bomont, Ron, and I have independently applied this model using very different methods to the Disco, and agree that the strength of the Disco valve anchorage screws sets an ultimate failure pressure no higher than 4862psi (Ron), to 6600psi (Bomont) with me in the middle at 6000. I'd say that spread comprises usefully close agreement.

Certainly better than simply shrugging our collective shoulders until somebody wants to sacrifice a perfectly good gun.



Steve

Air Conserving MSP 392
GTX Generation II 2-Stage Trigger
Benjamin SuperSear
Crosman Custom Parts
Big Ed Airguns

 
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(Login randyfb)
Crosman Forum Member
96.51.23.134

I don't disagree,

June 23 2009, 7:31 PM 

but doing a couple of actual destructive tests will be the ultimate yeah or neah on the whole issue. how could anyone deny or refute real world evidence?

regards,

fireball.gif

 
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(Login pneuguy)
Crosman Forum Member
68.221.11.159

How? Easy. Exactly the same way they're now denying Bomont's. nt

June 23 2009, 7:33 PM 


 
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(Login randyfb)
Crosman Forum Member
96.51.23.134

properly documented?

June 23 2009, 9:04 PM 

I suppose there'll always be a conspiracy nut or two but IMO, it would still be the final say for the open minded.

regards,

fireball.gif

 
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(Login pneuguy)
Crosman Forum Member
68.221.11.159

The only folks who aren't already convinced are those who pretend to believe...

June 23 2009, 9:13 PM 

...that Bomont's test was faked and those three #8 screws in the Disco can somehow withstand 4900 lbs (i.e., 11000psi) of shear force. That's 1633lbs each!

I don't know if the polite term for such folks is "closed minded," or "absent minded." happy.gif

Steve

Air Conserving MSP 392
GTX Generation II 2-Stage Trigger
Benjamin SuperSear
Crosman Custom Parts
Big Ed Airguns

 
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(Login randyfb)
Crosman Forum Member
96.51.23.134

I'm in the 6000psi camp,

June 23 2009, 9:18 PM 

and I suspect most people who have worked with pressure vessels of some kind are, but there are those who don't have that background and won't make the leap without being shown in fine detail.

JMO,

fireball.gif

 
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(Login pneuguy)
Crosman Forum Member
68.221.11.159

I'd venture to say that anyone with even the slightest interest in the question...

June 23 2009, 9:35 PM 

...of safe fill pressures is in the 6000psi (or thereabouts) camp.

All the others are only interested in defending an advertisement of a power tune based on overfilling the Disco.

And the advertiser.

Steve


    
This message has been edited by pneuguy from IP address 68.221.11.159 on Jun 23, 2009 9:36 PM


 
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(Login Voltar1)
Crosman Forum Member
72.25.192.4

Got 5000psi on it now see above test

June 23 2009, 10:03 PM 

holding fine with 5,000psi on a 2240 tube, three 8-32 low profile SHCS of 200,000psi strength threaded into an aluminum fake valve body.

Walter....

 
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Ron
(Login oo7fuzz)
Crosman Forum Member
65.31.184.65

Walter, do you have the screw head in shear position?nt

June 23 2009, 10:33 PM 


 
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(Login Voltar1)
Crosman Forum Member
72.25.192.4

6500 psi all is well

June 23 2009, 10:19 PM 

tube has grown 0.001" in diameter
no fastener issues nor fill plug threads.

Walter....

 
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(Login Trojan1994)
Crosman Forum Member
67.170.202.238

So if a C02 Based 2240 tube can handle 10,000 psi without failing...

June 24 2009, 12:08 AM 

is the Crosman information of 11,000psi that far off? Does 2,001 psi or 2,050 psi or 2,100 psi appear hazardous? More so that adding aftermarket trigger sears? happy.gif

Regards,

Tony

 
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Current Topic - Discovery Rifle's Air Tube & Valve Assemblies Tested to 11,000psi hydrostatically! LINK
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