Pressure decay test

The arrangement is then placed in a furnace, heated to 800°C, and the pressure decay test is repeated. The setup can be subjected to thermal cycles with pressure decay tests at room temperature and at 800°C. A good hermetic seal, however, will not show any pressure decay at a low pressure differential. The results of one series of tests using a glass composite material that has a glass transition temperature (Tg) of about 700°C, at 5 psi are shown in Figure 5.10. The combination of pressure and thermal cycle tests showed that the seal is capable of withstanding the pressure... 

Pressure Hold (Pressure Decay) Test . Pressure hold tests require a wetted filter to be pressurized with gas. Further supply of gas is then shut off. The pressure decay in the filter is monitored over time and compared to predetermined standards. 

Pressure decay tests are mainly used as prefiltration integrity tests for cartridge filters. 

Hydrophobic gas filter can be tested with the water intrusion test (WIT). Hydrophilic liquid filter are usually tested with water, the often used test method is the pressure decay test (PDT) a variation of the forward flow test (FFT). 

ACH aluminium chlorohydrate GAC granulated activated carbon PAG powdered activated carbon PDT pressure decay test TMP trans-membrane pressure PV pressure vessel O-I outside-inside I-O inside-out CA cellulose acetate PES polyether sulphone PVP polyvinylpyrrolidone PVDF polyvinylidene fluoride. Source Based on [91]. 

Pressure decay test (PDT) — every 24 h for 4 min to test fibre integrity. 

Pressure Decay Test (PDJ)—Filled This test involves applying pressurized air to the feed side at a predetermined level below the bubble point and then isolating. When the pores of a membrane are flUed with liquid and air pressure is applied to one side of the membrane, surface tension prevents the liquid in the pores from being blown out by the air pressure below a certain minimum pressure known as the bubble point. The predetermined pressure directly relates to the size of defect under investigation [Drinking Water Inspectorate (DWI), 2001]. 

Pressure Decay Test—Drained This is very similar to the PDT-fiUed, but in this case the module is drained on both sides of the element so that the membrane is only wetted. 

This is the most common test method employed to qualify the leak characteristics of a new seal material. The test method involves applying the seal between two ceramic discs or between a ceramic and a metal disc, pressurizing the cavity formed by the seal and monitoring the pressure decay as a function of time.22 Alternatively, a metal tube and a ceramic disc can also be used [34], Typically, the cavity is pressurized to about 2 psi and the leak rate is determined by the pressure decay as a function of time. These tests can be done at room temperature or elevated temperatures. Similar test arrangement has also been used to test a plastically deformable brazed metal seal between fuel cell anode material and Haynes 214 washer [35], The cavity is pressurized to measure the rupture strength of the seal material. 

Test methods described in the literature inelude the bubble method, helium mass speetrometiy, liquid tracer (dye), head spaee analysis, vacuum and pressure decay, weight loss and gain, and high voltage leak deteetion [6]. 

Pressure test Proper functioning check valve Pressure decay <75psi/min No leak from the pump 6 months... 

If the normalized salt rejection is low or the normalized permeate flow is high, the integrity of the membrane may be in question. The vacuum decay test is a direct test for the integrity of a spiral wound RO membrane module. The test is best used to identify leaks within the membrane modules rather than leaks due to chemical attack. The test requires the isolation of an individual membrane module or the entire pressure vessel. A vacuum is then pulled on the membrane(s) and the rate of decay in pressure is observed. A decay of greater than 100 millibar per minute is indicative of a leaky membrane. Refer to ASTM Standards D39235 and D69086 for a more detailed review of the technique. 

Evaluating the integrity of the container can be done in several ways. Two of the most common tests are dye penetration and microbial ingress. Container closure systems stored in a dye solution and exposed to pressure and vacuum cycles are examined for dye leakage into the container. The microbial ingress is similar in fashion but determines the microbial contamination of the contents when soaked in a media contaminated with bacteria. Other quantitative tests that can be run are vacuum/pressure decay, helium mass spectrometry, and gas detection. 

The pressure hold test is a variant of the diffusive airflow test. The test set-up is arranged as in the diffusion test except that when the stipulated applied pressure is reached, the pressure source is valved off (Fig. 9). The decay of pressure within the holder is then observed as a function of time, using a precision pressure gauge or pressure transducer. 

It is essential that the microbiological particle passage test is performed as part of the development of new sterile formulations. Because of its very specialized nature, the test is normally performed only by the filter manufacturers, who then provide limits for secondary physical tests (e.g., bubble point, pressure decay, forward flow, etc.), which can be applied to verify the pore size rating and integrity of the membrane filters. 

Water penetration rates are usually calculated according to the gas laws from measurement of pressure decay upstream of the filler over the whole period of testing with the gas (air) volume above the fluid held constant. They are therefore subject to temperature variations. Although the principle of the water penetration test is sound, and the avoidance of the use of potentially adulterating solvents is attractive, the low rates of water penetration calculable from only very small pressure drops within test systems have raised doubts about the robustness of the method for routine application in its contribution to the decision-making process. 

Answer by Author The flange pressures in the load decay test were in great excess of realistic values. Several specimens indicated that they had leveled out after 30 min. The curves were not corrected for check valve leakage in the hydraulic loading setup described. In an actual application, retightening of flanges may possibly be helpful, in light of the fact that essentially no compression set or creep is apparent. 

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