25.08.2026
The most critical quality control stage in the manufacturing and repair of industrial valves is leak testing. Gate, globe, ball, and butterfly valves must be tested to international standards before being shipped to site or reconnected to the line after repair. These tests certify the integrity of the body and the leak-tightness of the closure element.
1. Body (Shell) Hydrostatic Strength Test
The body test verifies the pressure resistance of the valve's pressure-containing walls, stem packing, and body-bonnet joint area:
- Procedure: The valve is placed in a partially open position, and its inlet and outlet ends are blinded. Air is fully vented and the valve is filled with test fluid (usually corrosion-inhibited water).
- Test Pressure: As required by the applicable standard, a pressure equal to a set multiple of the valve's nominal working pressure (typically 1.5 times) is applied in stages.
- Inspection: During the specified hold time, the body casting is checked for sweating, cracks, or fluid leakage from the packing.
2. Seat Leak Test
The seat test measures whether the valve's closure element (disc, or ball) holds back fluid along the line while in the closed position:
- High-Pressure Liquid Test: The valve is fully closed. Hydrostatic pressure of roughly 1.1 times the design pressure is applied from one side while allowable leakage (drop count or flow rate) is measured from the open side.
- Low-Pressure Gas Test: Particularly for soft-seated ball or butterfly valves, air or inert gas is used at low pressure to detect micro-leaks with a sensitive flow meter or water bath.
- Bi-Directional Check: For valve models rated for bi-directional sealing, the test is repeated separately for both flow directions.
3. Backseat Test
The backseat sealing mechanism found in globe and gate-type valves relieves pressure on the packing area when the valve is fully open. In the backseat test, the valve is fully opened, packing pressure is released, and it is checked for stem leakage from the back at the rated pressure.
Test Safety in the Field and in the Workshop
During hydrostatic tests carried out under 24/7 on-site service at oil refineries, fuel terminals, chemical plants, and power plants, safety cages and calibrated digital pressure gauges must be used against high pressure. Valves that pass testing successfully are then ready for installation.
Frequently Asked Questions
Why is the body hydrostatic strength test applied above the nominal pressure rating?
It is tested with a high safety margin, in line with applicable standards, to detect potential casting porosity, micro-cracks, and weld defects and to prevent the valve body from bursting under sudden pressure surges.
What does zero leakage mean for valves?
Zero leakage is the highest sealing class, indicating that during the test period, no air bubble or fluid drop passes through visually or via flow meter — particularly relevant for elastic/soft-seated valves.