Testing Beeman Chief Valve Screws to Failure- SECOND VIDEO added reply #42

[lloyd-ss]

I am working on getting the test piece apart so that at least the tube can be re-used for testing the screws that Ribbonstone is sending me.
Here is a pic of the aluminum plug pushed partially back out of the tube. The way the screws sheared off, it is not coming out without a fight. The head that popped off is laying on the tube for reference.

[Rob M]

yea, that cant be good.

[rsterne]

Left-hand drill bit?....

Bob

[lloyd-ss]

Left-hand drill bit?....

Bob

Yup, I should to get a few of those.  The need has come up more than once. Seems like one of those things you struggle with for years, and then after you deal with it, you're wondering, "what took me so long?" LH drill bits added to the shopping wish list.

[PeterL]

Thanks for sharing the test results. Very informational.

Have this test been done for the Mrod valve screws?

Peter

[lloyd-ss]

Thanks for sharing the test results. Very informational.

Have this test been done for the Mrod valve screws?

Peter

I did a test of the Marauder type screws in the new lightweight weight M-Rod air tube made by JSA. Even though this wasn't a test of the OEM M-Rod screws, indications are that the screws are more than up to the task.  Here is that thread.
https://www.gatewaytoairguns.org/GTA/index.php?topic=138623.0
 
I also did some testing of the OEM Disco screws and the upgraded alloy low profile SHCS that a lot of folks install in the Disco. rsterne referenced that particular thread earlier in this thread.
Lloyd

[PeterL]

Thanks for sharing the test results. Very informational.

Have this test been done for the Mrod valve screws?

Peter

I did a test of the Marauder type screws in the new lightweight weight M-Rod air tube made by JSA. Even though this wasn't a test of the OEM M-Rod screws, indications are that the screws are more than up to the task.  Here is that thread.
https://www.gatewaytoairguns.org/GTA/index.php?topic=138623.0
 
I also did some testing of the OEM Disco screws and the upgraded alloy low profile SHCS that a lot of folks install in the Disco. rsterne referenced that particular thread earlier in this thread.
Lloyd

Thanks Lloyd. I did see that test that you performed. It showed the tube failing but the screws were still intact. I'm curious about there strength with this current test you did for the screws specifically. The reason for my asking is seeing what the max fill pressure these screws can withstand repeatedly.

Peter

[lloyd-ss]

Thanks for sharing the test results. Very informational.

Have this test been done for the Mrod valve screws?

Peter

I did a test of the Marauder type screws in the new lightweight weight M-Rod air tube made by JSA. Even though this wasn't a test of the OEM M-Rod screws, indications are that the screws are more than up to the task.  Here is that thread.
https://www.gatewaytoairguns.org/GTA/index.php?topic=138623.0
 
I also did some testing of the OEM Disco screws and the upgraded alloy low profile SHCS that a lot of folks install in the Disco. rsterne referenced that particular thread earlier in this thread.
Lloyd

Thanks Lloyd. I did see that test that you performed. It showed the tube failing but the screws were still intact. I'm curious about there strength with this current test you did for the screws specifically. The reason for my asking is seeing what the max fill pressure these screws can withstand repeatedly.

Peter

The Marauder rifle is rated for a 3,000 psi max fill pressure by Crosman, and that should be observed.  The screws will handle a lot more force than that before FAILING, but you should never operate any equipment close to its failure point.  Allowing at least a 3.5 to one safety factor is a recommendation made by some engineering organizations.  So, if the screws fail at a fill pressure of 10,500psi, they a safe maximum operating pressure is 3,000 psi.

I have never tested the Marauder screws to failure, and honestly, I do not know if they are the weak link in the pressure system of the Marauder. Something else might very well fail before the screws do.
Lloyd

[Kinetic45^]

Hummm...
Another situation where to get 3 screws you have to buy 100.
Wish we could get a group effort going to share with each other

for example, I have 90 (kept 10) 1/8 BSPP bonded seal washers used in our HPA fittings sitting on the shelf looking for good homes.  Paid $14 for them at a hydraulics supply company.
H, I would even pay the $1 shipping to put 5ea into an envelope so other guys don't have to pay $5 ea ripoff price charged by the AG outfits.

I have a Chief and have no plans to hotrod it but would change the screws for 'peace of mind' but it irks me to buy n waste most of a box of screws

[lloyd-ss]

Hummm...
Another situation where to get 3 screws you have to buy 100.
Wish we could get a group effort going to share with each other

for example, I have 90 (kept 10) 1/8 BSPP bonded seal washers used in our HPA fittings sitting on the shelf looking for good homes.  Paid $14 for them.
H, I would even pay the $1 shipping to put 5ea into an envelope so other guys don't have to pay $5 ea ripoff price charged by the AG outfits.

I have a Chief and have no plans to hotrod it but would change the screws for 'peace of mind' but it irks me to buy n waste most of a box of screws

Carl, Yes, I agree. It is so easy to exchange ideas back and forth on the forum and the internet, wouldn't it be great if we could do the same with little odds and ends of special hardware. Somebody might volunteer on the Chief screws. We could have a hardware swap at the Funshoot.   

[rsterne]

There is a reason for the large safety margins used on pressure vessels, Peter, and you hit the nail on the head with your question....

The reason for my asking is seeing what the max fill pressure these screws can withstand repeatedly.

I highlighted the word REPEATEDLY because there is a big difference between the test Lloyd performed on the screws (a single load to failure) and what happens with cycling a pressure vessel hundreds or thousands of times, where the repeated stress may fatigue the material.... With steel, if you keep the stress applied to less than half the tensile strength, the cycle life is almost infinite.... Titanium is similar.... Aluminum has no such fatigue stress threshold, it continues to fatigue even if the applied stress is low, but at a much reduced rate.... In practical terms, if you keep the stress in most aluminum alloys below half the tensile strength, the cycle life is so great you can ignore it (perhaps millions of cycles)....

When a company designs a pressure vessel, and state a Maximum Safe Working Pressure (MSWP), they usually take into account a generous cycle life, and maybe even the possibility of some corrosion.... If you fill to a higher pressure, you are reducing the number of cycles to possible failiure, and that is the primary reason it is a bad idea.... You might get away with it once.... a hundred times.... or a thousand times.... but simply by using more pressure than the specified MSWP you are pushing it.... or at least shortening the safe lifespan....

Bob

[lloyd-ss]

x2 on what Bob just said in Reply # 30.
Lloyd

[PeterL]

There is a reason for the large safety margins used on pressure vessels, Peter, and you hit the nail on the head with your question....

The reason for my asking is seeing what the max fill pressure these screws can withstand repeatedly.

I highlighted the word REPEATEDLY because there is a big difference between the test Lloyd performed on the screws (a single load to failure) and what happens with cycling a pressure vessel hundreds or thousands of times, where the repeated stress may fatigue the material.... With steel, if you keep the stress applied to less than half the tensile strength, the cycle life is almost infinite.... Titanium is similar.... Aluminum has no such fatigue stress threshold, it continues to fatigue even if the applied stress is low, but at a much reduced rate.... In practical terms, if you keep the stress in most aluminum alloys below half the tensile strength, the cycle life is so great you can ignore it (perhaps millions of cycles)....

When a company designs a pressure vessel, and state a Maximum Safe Working Pressure (MSWP), they usually take into account a generous cycle life, and maybe even the possibility of some corrosion.... If you fill to a higher pressure, you are reducing the number of cycles to possible failiure, and that is the primary reason it is a bad idea.... You might get away with it once.... a hundred times.... or a thousand times.... but simply by using more pressure than the specified MSWP you are pushing it.... or at least shortening the safe lifespan....

Bob

And that's the big question Bob. I'm looking at having a titanium tube made at 25 5/8" inches for my rifle ( I know, I know. Why not put a bottle on it?). I want this rifle to look like a traditional marauder but under it's looks, have a bark/bite like no other. There's just so much custom parts on this rifle, it's not even funny. Anyway, that's the reason for wanting stronger screws. My max fill would put me between 3400-3600 psi but safety is my number one priority.

How would you go about tackling this Bob if you were to do it exactly the way I've mentioned. Am I missing anything. Depending on thickness of tube I might have to worry about sear engagement, fill assembly strength, bolt/hammer lug breaking if not fully closed etc..... Just trying to do this the right way.

Peter

[PeterL]

Thanks for sharing the test results. Very informational.

Have this test been done for the Mrod valve screws?

Peter

I did a test of the Marauder type screws in the new lightweight weight M-Rod air tube made by JSA. Even though this wasn't a test of the OEM M-Rod screws, indications are that the screws are more than up to the task.  Here is that thread.
https://www.gatewaytoairguns.org/GTA/index.php?topic=138623.0
 
I also did some testing of the OEM Disco screws and the upgraded alloy low profile SHCS that a lot of folks install in the Disco. rsterne referenced that particular thread earlier in this thread.
Lloyd

Thanks Lloyd. I did see that test that you performed. It showed the tube failing but the screws were still intact. I'm curious about there strength with this current test you did for the screws specifically. The reason for my asking is seeing what the max fill pressure these screws can withstand repeatedly.

Peter

The Marauder rifle is rated for a 3,000 psi max fill pressure by Crosman, and that should be observed.  The screws will handle a lot more force than that before FAILING, but you should never operate any equipment close to its failure point.  Allowing at least a 3.5 to one safety factor is a recommendation made by some engineering organizations.  So, if the screws fail at a fill pressure of 10,500psi, they a safe maximum operating pressure is 3,000 psi.

I have never tested the Marauder screws to failure, and honestly, I do not know if they are the weak link in the pressure system of the Marauder. Something else might very well fail before the screws do.
Lloyd

Thank you very much for your responses Lloyd. I truly hope I'm not derailing your thread even though it's pertaining to valve screws of a different rifle? Sorry, if I am and will start a new thread if you would like me to do so.

Peter

[lloyd-ss]

Peter, Yes, you've described a whole 'nother thread about air tube design. Send me a PM if you like.
Lloyd

[PeterL]

Peter, Yes, you've described a whole 'nother thread about air tube design. Send me a PM if you like.
Lloyd

Thanks Lloyd. My apologies. PM sent.

Peter

[rsterne]

There are a LOT of things to look at, from the tube strength to the threads at the ends, to how the valve is anchored, not only for the shear strength of the screws, but the forces they put on the tube wall.... Assuming the tube is up to the job, and that the ID and wall of the tube is the same as an MRod (and we should never assume).... I would simply add a 4th screw like I did in my latest (6mm) build.... Best to have Lloyd take a look at the whole reservoir as a SYSTEM.... As you say, there are many OTHER things to consider, and it is surprising how many people forget that, while focusing on just one item....

Bob

[Rob M]

There are a LOT of things to look at, from the tube strength to the threads at the ends, to how the valve is anchored, not only for the shear strength of the screws, but the forces they put on the tube wall.... Assuming the tube is up to the job, and that the ID and wall of the tube is the same as an MRod (and we should never assume).... I would simply add a 4th screw like I did in my latest (6mm) build.... Best to have Lloyd take a look at the whole reservoir as a SYSTEM.... As you say, there are many OTHER things to consider, and it is surprising how many people forget that, while focusing on just one item....

Bob

Bob , we often discuss the tube wall and its ability to withstand longitudinal load.. But , the stress lengthwise is calculated as a factor of 1/2 that of the hoop stress. My question is ( LLOyd might chime also ) , in what fashion would the failure occur if the tube wall gave in to the rearward pressure from the screws ?? For some reason , if the screws don't shear, I cannot see a catstrophic failure in this fashion,.. I may be way off, hence I'm asking

[rsterne]

The video where Lloyd tests the new aluminum tube from JSA will give you your answer.... Admittedly it happened early because of the proximity of the bottom screw hole to the sear slot.... but the screws plowed through the tube, ripping slots until the O-ring vented.... We call this type of failure "exceeding the bearing load" of the tube wall, and it shows up first as a buckling or stretching of the tube wall where the screw heads are pushing on it.... or as a "tearout (shear) failure" if the hole is too close to the end of the tube.... The failure in the aluminum tube Lloyd tested started as the latter (on the bottom hole), but ended as the former (on the other two holes)....

While you are correct that the londitudinal stress on the tube FROM THE AIR PRESSURE INSIDE is only half the hoop stress from that pressure.... the localized stress on the compression side of the holes in the tube is MUCH greater because the entire load on the valve is concentrated on just the area of the (three) holes....

Bob

[Rob M]

makes perfect sense.thx . I think the equations are better applied to scuba tanks and large propane tanks where the load is assumed symmetrical.. whereas , that 1000 plus lbs resting on .100 sq inches is certainly not as ideal. going to search Lloyds youtube now