# Volume of compressed helium gas needed for FE test on ball valves

I'm currently doing a case study to find out the exact volume of helium gas required for FE tests on ball valves regards to the valves' volume and pressure class and the number of helium tanks needed for it (assuming the test is being done at room temperature)

The specifications of helium gas that is being supplied to the test bench is as follow :

Helium 5.5 Purity: 99.9995
Size: X50S Pressure: 200B

1. The gas capacity (with regards to the Helium Gas) 8.57NM3
2. The water capacity. 50L
3. The dimension of the cylinder tank .1,51M height
4. The weight of the cylinder tank (with and without the Helium Gas) Net fill weight 1.51KG. Gross weight vary.
5. The maximum pressure in which the tank can be operated. Max working pressure 200 Bar
6. The valve outlet. BS3 Brass

Therefore my question is can the gas law be used to find the volume of helium gas needed for the tests and what are the variables that is needed in finding the volume?

ex: P1 = Valve Maximum Pressure, P2 = Helium Cylinder Tank Pressure, V1 = Valve Internal Volume (has been calculated), V2 = Volume of Helium Gas Needed (required) Standards for the FE test are:

1. ISO 15848 Part 1
2. Shell SPE 77/312

Thank you

Edit:

In simple term, I would like to know what is the volume of helium gas needed to pressurize the valve to reach a certain test pressure? Given that, the helium cylinder tank has a max working pressure of 200 Bar and a volume of 8.57Nm3. So how much helium gas is needed from this cylinder to pressurize a valve with an internal volume (ex : 0.91594m3) to a test pressure of 19.6 Bar

• The volume that the helium gas occupies will be equal to the valve internal volume. Depending on the testing pressures, you will probably need to include the compressibility factor for helium in the ideal gas law calculations. The amount of gas used per fugitive emission test is better tracked by knowing how much mass is needed to get the valve internal volume upto testing pressure. – J. Ari Nov 27 '20 at 2:22
• We can assume helium as an ideal gas, therefore the compressibility factor can be neglected right? 'by knowing how much mass is needed to get the valve internal volume upto testing pressure" can I get more explanation on this. – Velruban Sivananthan Nov 27 '20 at 6:08
• What is the test pressure for the FE test? You can look up the real density from a source like the NIST Webbook and confirm if Z is approx. to 1 or not at the test pressure. After you have that Z value, you can use PV=nRT to determine the number of moles of helium (and therefore mass of helium) needed to take the valve volume (V) up to the test pressure (P) at the testing temperature. – J. Ari Nov 27 '20 at 16:20
• In simple term, I would like to know what is the volume of helium gas needed to pressurize the valve to reach a certain test pressure? Here is an example : Given that, the helium cylinder tank has a max working pressure of 200 Bar and a volume of 8.57Nm3. So how much helium gas is needed from this cylinder to pressurize a valve with an internal volume (ex : 0.91594m3) to a test pressure of 19.6 Bar (z of helium = 1.005) – Velruban Sivananthan Nov 29 '20 at 8:26
• My second comment tells you what calculation you need to do, with one correction to the equation - PV = ZnRT. But since you're saying the Z value for He at 19.6 barg is 1.005 it won't really matter. – J. Ari Nov 29 '20 at 21:18