How to slow down the venting of a 9000 psi volume? - 0.003" oriface not enough
How to slow down the venting of a 9000 psi volume? - 0.003" oriface not enough
(OP)
Hello all - I'm a test engineer, and one of the tests my technicians perform is a proof test on a 42 cubic inch container, at 9000 psi. The catch is that one of the requirements of this test is the container cannot be filled or vented at a rate faster than 1000 psi/min (or 2000 psi/min for a 3 second moving average). This has become a huge problem when venting the container after the test and this rate is often exceeded, especially by inexperienced technicians (we vent it through a regulator to try to control the venting better. A 0.003" oriface was installed in the pressure line between the container and the vent, but it appears to only be effective at lower pressures - say 1000 or so.
I'm a bit at a loss on how else to slow this venting down - I haven't found a smaller orifice that would work with such high pressures. I believe the customer's venting requirements are based on a maximum allowable flow rate and the 1000 psi/min covers the worst case scenario of dropping from 9000 psi to 8000 psi in a minute.
The (simplified) current setup is that a tank of gas is connected to a booster pump, which is connected to a regulator. This regulator then goes into a gas line that goes into my container. There are two valves on the supply line - one is an isolation valve for the container, and another is a valve to vent the system.
One option I'm considering is to better automate the test to remove human error, but I want to also find a physical solution to prevent the vent rate from being exceeded in case of program failure - if the program aborts and brings things to a "safe state," the container will be vented.
Any help is greatly appreciated.
I'm a bit at a loss on how else to slow this venting down - I haven't found a smaller orifice that would work with such high pressures. I believe the customer's venting requirements are based on a maximum allowable flow rate and the 1000 psi/min covers the worst case scenario of dropping from 9000 psi to 8000 psi in a minute.
The (simplified) current setup is that a tank of gas is connected to a booster pump, which is connected to a regulator. This regulator then goes into a gas line that goes into my container. There are two valves on the supply line - one is an isolation valve for the container, and another is a valve to vent the system.
One option I'm considering is to better automate the test to remove human error, but I want to also find a physical solution to prevent the vent rate from being exceeded in case of program failure - if the program aborts and brings things to a "safe state," the container will be vented.
Any help is greatly appreciated.





RE: How to slow down the venting of a 9000 psi volume? - 0.003" oriface not enough
Also check that the vent line materials of construction are suitable for the lowest temp seen during depressurisation, else there may be a risk of brittle failure if the vent line ruptures due to high vibration.
RE: How to slow down the venting of a 9000 psi volume? - 0.003" oriface not enough
Remember - More details = better answers
Also: If you get a response it's polite to respond to it.
RE: How to slow down the venting of a 9000 psi volume? - 0.003" oriface not enough
That is, assume the Delta P from 9000 psig to 8000 psig happens when the gas expands by 10% - but get the exact number.
Translate that 10% drop in pressure => 10% gain in volume => 4.2 cubic inch => how long of a 9000 psig rated tube 1/2 inch in ID. Assume, for discussion, that length is 4.2 inches.
Run your vent line from the container to a vent valve V1 through the orifice (no sense in throwing it away yet) to the a 2.0 length of 1.2 ID tube to a vent valve V2 to a second 1/2 ID tube to a vent valve V3 to atmosphere (or your recovery PV).
Process. End of test.
Close all valves, vent the container to the first tube through V1. Pressure goes down quickly, but cannot go lower than 8500 psig (or so). Close V1. Don't vent from the container yet, but open V2 to reduce the surge pressure by filling both Tube 1 and tube 2. Open V1 again at time = 2.0 minutes. Now, both tubes are at equilibrium pressure with the original container, and the "surge" drop is reduced to within spec because it went from 9000 psig to 8100 psig in a guaranteed minimum of two minutes. Plus, the half-filled tubes eliminate the "shock" by themselves acting as two more slowly-filled "dampers" which is what you really want anyway.
At t = 3.0 minutes, close V1, open both V2 and V3 and vent both tubes to atmosphere.
At t = 3.3 minutes, or when the tubes are empty, repeat everything above.
This cycles all three valves through another cycle, and repeats to reduce container pressure from 8100 psig to 7200 psig by repeating the steps above.
Repeat to go from 7200 psig to (0.9 of 7200 ) = 6480 psig.
Rinse, wash, and repeat until the orifice can maintain flow though the whole series with all three V1, V2, and V3 are open.
RE: How to slow down the venting of a 9000 psi volume? - 0.003" oriface not enough
RE: How to slow down the venting of a 9000 psi volume? - 0.003" oriface not enough
RE: How to slow down the venting of a 9000 psi volume? - 0.003" oriface not enough
RE: How to slow down the venting of a 9000 psi volume? - 0.003" oriface not enough
Stay away from simple orifice plates as their permanent pressure drop is only a fraction of the measured dP.
David Simpson, PE
MuleShoe Engineering
In questions of science, the authority of a thousand is not worth the humble reasoning of a single individual. Galileo Galilei, Italian Physicist
RE: How to slow down the venting of a 9000 psi volume? - 0.003" oriface not enough
This tube is strong (cold worked stainless), it wouldn't take a very long piece to create a significant pressure drop.
= = = = = = = = = = = = = = = = = = = =
P.E. Metallurgy, Plymouth Tube
RE: How to slow down the venting of a 9000 psi volume? - 0.003" oriface not enough
It is better to have enough ideas for some of them to be wrong, than to be always right by having no ideas at all.