The
3K Walking Dead
It
has become painfully obvious that I need to include a section on CO2
burst protection. Though the subject matter may be a little dry, the
amount of inaccurate and sometimes dangerous misinformation is at
this writing is more prevalent than the real information. Some of the
misinformation has been around since the advent of paintball but the
most dangerous information was born with the introduction of HPA.
Those who have followed my postings will know that I am no fan of HPA
because of it's inherent dangers magnified with the adverse nature of
atrophy. Now that part of the paintball industry has created a
serious new threat to the CO2 users. The threat I am referring to is
the use of 3K burst discs on 1800 rated CO2 paintball tanks. This is
not a malicious action by HPA proponents but the assortment of burst
discs introduced have allowed bad decisions to take place. Tanks left
in the sun pop the disc. Solution? Add a higher rated disc, we have
them in stock. Wrong. But obviously this was the choice made and it
seemed to work so well in has become standard. The problem is the
vacuum of data that is available on pressurized vessel protection
and it is this continued lack of information that has sustained
dangerous practices.
In the paintball industry the pressures associated with
the working mechanics of CO2 are considered high pressure. In the Gas
industry CO2 is regarded as a low pressure gas. We need to understand
that there are two industries involved on this topic and definitions
are NOT transferable but often confused. The pressure level in the
gas industry refers to the natural pressures of contained gas, The
pressure level in the paint-ball industry refers to the final
operating pressures of the marker itself. Most of the information we
now have on paintball comes from the marketing industry, conversely
the information in the gas industry is based on manufacturing and
handling safety standards and hard science.
A
common sense that something is seriously wrong came when I looked
into the topic of volumetric testing or as the paint-ball industry
calls it, Tank re-certification. Specifically important is the fact
that tanks are tested in the following manner, The valve is removed,
The tank is placed in a reinforced vat containing water. The Tank to
be tested is filled with water and hydraulically pressurized to the
to a specified pressure. Tank distortions are measured and if the
tank survives the test, the tanks recovery dimensions are checked.
All measurements are then compared with industry accepted standards
and the tank is passed or failed. Hydraulic pressurization is used
for safety reasons. Water cannot be compressed so that the static
pressure has little stored energy should a catastrophic failure
occur. Furthermore, the test is under water in a sturdy tank to
protect testers from tank fragmentation on catastrophic tank failure.
The hydro-test pressure for CO2 tanks is 5/3 the tanks stamped
operating pressure. For a tank stamped 1800 this would be 3K or 3000
psi. Now on the flip side. Pneumatics have a high level of stored
energy which on catastrophic tank failure is violently released
adding substantial force to fragmentation. For this reason testing
pneumatically is strictly forbidden in even when the tank is in a
protective enclosure buffered with water. Now consider that if you
have a 3K burst disc that is designed to burst at between (-)10 or
(-)20% up the the listed burst pressure, You are potentially stress
testing your tank with pneumatic pressure right next to your face. I
hope that you can see the problem here. A safety device means just
what it implies, Safety. How can a device that allows a tank to
pressurize to levels used in stress testing, using a method
(pneumatic) that is specifically forbidden for safety reasons be
called a safety device. Plainly, it can't. The 5/3 burst disc safety
standard is a sham. Unfortunately nobody questioned the practice and
it has found its way to be the norm so now most paint-ball vendors
push the 3K disc for your 1800 rated CO2 tanks. Being the norm does
not make it right, or safe. Greatly adding to this confusion is a
lack of uniformity in the identification of burst discs. Some list
the tanks service pressure and some list the burst pressure. At no
point should you use a disc from an unknown manufacturer or a
manufacturer that will not release burst specs. If you are using a
1800 service rated tank then 3K should never be used in any case. At
best your tank is exposed to 3000 psi which is hydrotesting pressure,
at worst if the 3K is actually working pressure, your tank is exposed to between 3750 psi to 4285psi which will most likely
burst the tank first resulting in severe injury or death.
The
burst discs in the HPA market are designed for HPA regulators, not
CO2 tanks. They are 1.8K, 3K, 5K, and 7.5K. Whether this is a service
rating or a burst rating is never defined in writing. Stay away
unless you treat them as service ratings. The worst case then is that
a 1.8K unified disk could burst as low as 1440 psi if it's actually a
lower quality burst rated disc. It is better to burst low than burst
a tank.
So
what is the correct burst disc for your tank? We need to go back to
basics and look at the industrial standards on pressured vessel
protection. The key information that we have is the tank stamp of
1800. This is the standard service pressure on the tank. This means
that the tank is designed to handle this pressure regularly and
repeatedly throughout its life. This implies a cap pressure to keep
within the 1800 service guidelines. Like fuses in electronics there
are different types of burst protections and their values vary a bit
for the service level they are protecting. The protection we are
using is usually a variation of the Sherwood burst protection 3/8-28
three hole vented plug over a flat disc sealed with a nylon washer
now being replaced with a unified unit consisting of disc and vent
plug. These fall under the flat disc style of protection for
pressurized vessels. The sizing on this type of protection shows a
maximum recommended operation ratio of 70% to 80% of the rupture
discs marked burst pressure. This indicates that the proper disc
protection falls between 2250 and 2571 PSI for a tank with a service
rating of 1800. On removing the vent bolt on my vintage 20 oz luxfer
cylinders Tippmann tank with original disc, I found a copper disc
with M16 printed on it. 16 Mpa(Megapascals) is equal to 2320.6 PSI
and this falls within required specs.
The
absolute answer for what size burst disc to get for your tank stamped
1800 is 2250 psi being ideal and the absolute max being 2571 psi.
Anything higher allows the tank to operate outside of the 1800
service rating and will shorten the life of the tank or could cause a
catastrophic failure during use. Burst discs are currently designed
to burst at -10%(high grade) or -20%(low grade) to +0% so a correct
2250 burst disc will burst at between 1980 psi (high grade) or 1760
psi (low grade) up to the maximum of 2250 psi, properly protecting an
1800 rated tank. Given the the choice I personally prefer the stand
alone disc over the unified system. Manufacturers make the unified
discs to the buyers specs so if a buyer wants unit marked 1.8 but use
a 3k disc, that is how they are made. The customer cannot know unless
they can see the markings on the disc itself and understand the code,
which is not always possible. I have seen unified burst discs
externally stamped 1.8 but the disc in the back was marked 18 on some
and 30 on others. The only way to be certain you have the correct
protection is when the disc comes with actual burst pressure
documentation. This should also list the parameters as to be
the(-)20% or the(-)10% accuracy.
I
would like to add at this point that a tank should not be modified
structurally. This weakens the tank and it must be condemned. This
includes material removal such as machining, sanding, or polishing.
It should also not be exposed to chemical alteration such as with
acid washing for re-anodizing. Damage or high heat exposure also
warrant that the tank be condemned. Contact the tank manufacturer for
the specifics in these areas.
So
what about the other CO2 tanks stamped with higher service ratings?
Below is a list of CO2 tanks with proper protection. At no time
should protection match or exceed its hydro-test pressure which is
also listed.
A
CO2 tank with a stamped 1800 service rating should have a burst disc
that bursts at 2250 psi best to 2571 psi extreme/ It is hydro-tested
at 3000 psi static with hydraulic pressure in a protective enclosure.
A
CO2 tank with a stamped 2266 service rating should have a burst disc
that bursts at 3000 psi best to 3237 psi extreme/ It is hydro-tested
at 3777 psi static with hydraulic pressure in a protective enclosure.
A
CO2 tank with a stamped 3000 service rating should have a burst disc
that bursts at 3750 psi best to 4286 psi extreme/ It is hydro-tested
at 5000 psi static with hydraulic pressure in a protective enclosure.
Remember
that the stamped number on the burst disc could be either the tank
service rating or actual burst rating. Only manufacturer specs can
tell you which, if you can find them. Treat all unknowns as tank
service ratings. Following a tanks service rating give you the full
life of the tank. Placing a larger disc allows a tank to operate at a
higher service rating than designed weakening the walls and
potentially causing failure during operation. My solution to tank
protection on hot days back then was laying a wet towel over the tank
between games. Currently, I won't carry a spare tank on my back
without first wrapping it it a damp Frog Tog and my burst disc are
all within industrial service ratings.
SML
Blogger.com user StrayBlackCatsMeow
Address http://68-special.blogspot.com/
Blog "The 68-Special from Tippmann Pneumatics Inc"
Blog Reference page number 11
Title - Get those 3K Burst discs off your 1800 psi service rated CO2 tanks or The 3K Walking Dead
Revised - 05/21/2017
