# Investigation of the Fluid Flow in a Large Ball Valve Designed for Natural Gas Pipelines
## 4 Hydrostatic Tests  
The same DN500 ball valve studied by simulation was investigated by hydrostatic tests to verify whether leakages were really low for this ball valve with MM sealing and a DPE design. The hydrostatic tests represent the classic method to verify the quality of sealing. Water is used to visualize whether there are issues and to avoid explosion of an improperly designed valve. Standards that describe procedures to be used for tests on ball valves--namely, API 6D [19], SR EN 14313 [20], and ISO 5208 [29]--were used. Firstly, the hydrostatic shell test was performed, with the DN500 valve in the partially open position during the experiments. At the end of the body, the cavity was obturated to allow the transmission of the force generated by the full pressure from the end blanks to the body of the valve. The standards require that the pressure must be 1.5 times higher than the nominal pressure, which was 6.3 MPa for the investigated ball valve, which means an overpressure of 9.45 MPa. The valve must be tested at constant pressure, and the duration of the test must be in accordance with the nominal diameter of the valve. For example, for DN \(\leq\) 100 mm, the duration of the test should be 2 min; for DN between 150 mm and 250 mm, the duration of the test should be 5 min; for DN between 300 mm and 450 mm, the test duration should be 15 min; and for valves with DN 500 or larger, the test duration should be 30 min. The next test--the hydrostatic backseat test--was conducted in highly clean conditions, without sealants or lubricants on the ball or on the zone of the seats. The standards stipulate that the test pressure should be 1.1 times higher than the working pressure. For this test, the duration must also be in accordance with the nominal diameter, but the testing period is different from that of the previous test. For the valves with a nominal diameter over 500 mm, which is in the scope of this work, the test duration must be 5 min. The good quality of the sealing is demonstrated for the valves with soft sealing if there is no visually detectable leakage during the tests. According to the standard ISO 5208:2015 [29], for the valves with PMSS (primary metal-secondary soft) sealing or MM (metal-metal) sealing, the maximum allowable leakage fluid flow rate defines the category of safety to which the valve is supposed to belong. Information extracted from ISO 5208 is presented in Table 1.  
The test bench used for tests on the ball valve is presented in Figure 16. The equipment contains a hydraulic clamping system and control-panel-mounted test gauges capable of performing shell tests and seat tests on DN15-DN1000 flanged-end valves, in accordance with international test standards. The pressure used during the tests can be from 1.6 to 42 MPa. The test bench can use water, gas, or oil as the working fluid. The details and the schematic components of the test bench presented in Figure 16 were extracted from the DORY-YFI-B300 (JWZ-300) equipment manual [30]. In this work, the hydrostatic shell test used water as the fluid, and the hydrostatic backseat tests were performed with air. Figure 16: Structural schematic diagram. Components: 1. Hydraulic control station; 2. Panel of pressure gauge; 3. Panel of control button; 4. Pressure checklist; 5. Turning bench; 6. Clamping claws; 7. Clamping oil cylinder; 8. Moving bench; 9. Control valves; 10. Oil volume gauge; 11. Oil tank; 12. Electric box; 13. Low-pressure water supply pump; 14. Turning oil cylinder; 15. High-pressure water supply pump; 16. Moving oil cylinder; 17. Hydraulic and integrated components; 18. Oiling port; 19. Hydraulic motor and oil pump; 20. Pressurizing oil cylinder; 21. Oil draining; 22. Water draining [30].