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PCP's and Operating Pressures

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Hajimoto:
This topic can quickly get into the weeds and it is not my intent to try and navigate my way though the very complicated sets of standards, codes and accepted practices throughout the world but they need to be generally understood because applying the wrong standards can ruin someone's day.


The players:
 

* DOT- typically shown as DOT on part - Department of Transportation (previously ICC – Interstate Commerce Commission), which is the regulatory body that governs the use of cylinders.
* UN/ISO - typically shown as ISO on part - International Organization for Standardization, is a worldwide federation of national standards bodies (ISO member bodies). The work of preparing International Standards is normally carried out through ISO technical committees. Each member body interested in a subject for which a technical committee has been established has the right to be represented on that committee. International organizations, governmental and non-governmental, in liaison with ISO, also take part in the work.
* PED - typically shown as CE on part - The Pressure Equipment Directive (PED) is a European set of standards for the design and fabrication of pressure equipment and vessels. It provides the administrative requirement to allow for free placing on the European market without legislative barriers. It has been mandatory in Europe since 2002.
* SELO - typically shown as SELO on part - The SELO China Manufacturer License is an approval procedure that qualifies the manufacturer to produce pressure-bearing products, tanks and vessels.
That said, In the United States the DOT ( Department of Transportation ) enforce the standards set by CGA ( Compressed Gas Association ). In Europe the UN ( United Nations ) and EU ( European Union ) enforce the standards set by ISO ( International Standards Organization ). UN/ISO service pressures are at or above the common fill pressure of a DOT cylinder with a + 10% overfill designation. Also, UN/ISO cylinders contain friendly markings with service pressures rated in PSI and BAR.


ISO service pressures are at or above the common fill pressure of a DOT cylinder with a + 10% overfill designation. Also, UN/ISO cylinders contain friendly markings with service pressures rated in PSI and BAR. Keep in mind that the DOT test pressure are 5/3 times service pressure. Which means if the service pressure is 3000, divide that by 3 you get 1000, multiply that times 5. So a 3000 PSI vessel must endure a hydrostatic test of no less than 5000 PSI. So you can quickly see how someone could misapply the pressure vessel test results to the entire assembly and get into trouble very quickly.


All this said, one must know exactly what standards the pressure vessel(s) were manufactured to meet in order to know what their test limits are.


Remember that we are talking three different sets of numbers here, there are the manufacturers suggested pressure limits, operational limits and limit before failure, which brings us to the term "Maximum".There are two that must be understood in order to venture down the path of testing the limits.

* Maximum Allowable Operating Pressure -  is a pressure limit set, usually by a government body, which applies to compressed gas pressure vessels, pipelines, and storage tanks.
* Maximum Allowable Working Pressure - Is defined as the maximum pressure based on the design codes that the weakest component of a pressure vessel can handle.When I make suggestions of what I consider a safe operation pressure I use an engineering judgement based on general assessment of the information given by, stamps, spec sheets, material data and know industry standards.


The Gauntlet in .177 and .22 has a brass valve body with one fastener in the bottom that secures the valve body within the pressure tube. They do have a secondary safety should that single screw fail and the valve is forced rearward and that is part #19 which is held in place by the bottom stock screw and the magazine well screw from the top. The .177 and .22 are shipped with a operating pressure of 1100 PSI and I think a safe maximum operating pressure of this arrangement is 1400 PSI. That does not mean that it cannot operate at higher pressures, but higher rated safeties would need to be employed (burst discs, hardened fasteners) to comfortably go there.


The Gauntlet in .25 has a Stainless Steel valve body and 3 fasteners that secures the valve body within the pressure tube. They also have the secondary safety that uses part #19 which is held in place by the bottom stock screw and the magazine well screw from the top. The .25 are shipped with a operating pressure of 1900 PSI and I think a safe maximum operating pressure of this arrangement is 2100 PSI. That does not mean that it cannot operate at higher pressures as the .25 has a more robust overall build and I have seen the .25 run as high as 2600 PSI, but I cannot endorse this as an operating pressure as there is not clear data available on the materials and fasteners used in construction of this rifle.


The long, longer, if you don't know, take the conservative approach and be safe! So yes, manufacturers offer a safe maximum operating pressure which has some wiggle room, to press a mechanical system to its structural limits costs something and it has been my experience that that cost is service life. This service life reduction can be the fasteners that are holding the bottle drop block in place which have no safety other than the screws themselves which if sheared, sends block and bottle skipping across a shop, range or home.


Do you home work and investigate and request as much data as you can from the manufacturer before pushing the limits of pressure vessels you have no idea what their assembly pressure limits are.


Thanks,
Hajimoto

CraigH:
Thanks for an introduction to the "players"    Some previously known, some not.

bear air:
Thank you for the write up Haj, HPA is not to be taken for granted.

scion19801:
nice write up hajimoto. Always good things coming from you and others who are knowledgeable.

archellas:
Haj,

Thank you for providing info about this! HPA is no JOKE!

If you have ever seen a tire blowout (from about 35 psi pressure) you SHOULD understand what 3000+ psi means (I HOPE!)

Cheers

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