In hydrostatic testing of CNG cylinders, the water jacket plays a few critical roles. Here’s a clear, exam- and field-friendly breakdown 👇
1. Measuring Total Expansion
The main function of the water jacket is to measure the total volumetric expansion of the CNG cylinder when it is pressurized.
The cylinder is placed inside a sealed water-filled jacket
When pressure is applied, the cylinder expands
This expansion displaces water, which is measured accurately
This tells us how much the cylinder stretches under test pressure.
2. Measuring Permanent Expansion
After releasing the pressure:
The cylinder contracts
Any expansion that does not recover is called permanent expansion
The water jacket helps calculate this by comparing:
Total expansion vs. recovered (elastic) expansion
If permanent expansion exceeds the allowed limit (usually ≤ 10% of total expansion, depending on standards), the cylinder fails the test.
3. Ensuring Safety During Testing
If a cylinder were to rupture during hydro testing:
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