Definition
A pressure test in which a sealed container, such as an oxygen cylinder or fire extinguisher bottle, is filled with water (or another liquid) and pressurized to a specified level above its normal working pressure to confirm it can safely hold pressure without leaking, deforming permanently, or rupturing. The test is performed at scheduled intervals defined by regulation or the component manufacturer.
Plain English
A safety test where a pressure container is filled with water and squeezed to a higher-than-normal pressure to make sure it is still strong enough to use. Water is used instead of air because if the container fails, water will not explode outward the way compressed air would.
Context Anchor
Seen in aircraft maintenance records and inspection requirements for pressure bottles, such as oxygen cylinders and fire-extinguisher bottles.
Derivation
From Greek hydro- meaning water, and statikos meaning at rest or standing. Together it describes pressure exerted by a liquid that is not flowing. The test uses the steady pressure of trapped water to check the container's strength.
Why Pilots Care
Confirms that high-pressure containers remain safe and will not fail in flight, preventing loss of critical systems such as oxygen or fire suppression.
Intuition Check
A hydrostatic test is not a test for water in the aircraft system. It is a pressure test that often uses water because liquid does not compress easily, making the test safer and easier to control.
Example Sentence 1
The portable oxygen cylinder was removed from service because its hydrostatic test date had expired.
Example Sentence 2
After the repair, the fire bottle passed its hydrostatic test at 1.5 times service pressure with no leaks.