Pressure rise test

Example Once the vacuum vessei with a voiume of 20 i has been isoiated from the pump, the pressure in the apparatus rises from 1 lO mbar to 1 10 2 mbar in 300 s. Thus, in accordance with equation 5.2, the ieak rate wiii be 

If the container is evacuated with a TURBOVAC 50 turbomolecular pump, for example (S = 50 I/s), which is attached to the vacuum vessel by way of 

Naturally it is possible to improve this ultimate pressure, should it be insufficient, by using a larger-capacity pump (e.g. the TURBOVAC 151) and at the same time to reduce the pump-down time required to reach ultimate pressure. 

Today leak tests for vacuum systems are usually carried out with helium leak detectors and the vacuum method (see Section 5.7.1). The apparatus is evacuated and a test gas is sprayed around the outside. In this case it must be possible to detect (on the basis of samplings inside the apparatus) the test gas which has passed through leaks and into the apparatus. Another option is to use the positive-pressure leak test. A test gas (helium) is used to fill the apparatus being inspected and to build up a slight positive pressure the test gas will pass to the outside through the leaks and will be detected outside the device. The leaks are located with leak sprays (or soap suds, 5.4.5) or - when using He or H2 as the test gas - with a leak detector and sniffer unit (5.7.2). 

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The calculated value for qL based on a pressure-rise test (Equation 4.2) may not be solely due to leaks. Depending on the pressure range involved, virtual gas sources will also be involved. 

A stainless steel high vacuum system (V = 15L) has been pumped for 36 h and the pressure is 1 x 10 7 mbar. A pressure-rise test, starting at 10 5 mbar, shows a pressure of 1.5 x 10"3 mbar after 20 min. Calculate the amount of gas entering the chamber and comment on the source of the gas. 

A typical indication of leakage is the inability of the leaking system to achieve the expected working pressure. Pressure-rise tests are frequently carried out to assess the magnitude of the problem (Examples 4.3, 4.5-4.7,4.9). A convenient and highly sensitive method of leak detection and quantification uses He as a tracer gas and a He leak detector (MSLD). Some aspects of practical leak detection using MSLD were discussed (Examples 4.10-4.12). 

Figure 22.5. Schematic representation of a pressure rise test for dispersion quality.

The pressure rise test, although disliked by some practitioners, is a popular method for determining the endpoint of sublimation. By shutting off any gas flow into the chamber and isolating the condenser and the pumping system from the chamber, the chamber pressure is monitored. The absence of a pressure rise, within a period of ca. 2 s, is taken... 

The temperature of the advancing ice front can be determined using a barometric temperature measurement, via a pressure rise test (PRT) (see later), using a water vapour temperature diagram, as shown in Figure 5. In practice, this requires an interruption of the cycle and lacks the convenience of the continuous output from a thermocouple. 

Permeability of Freeze-Drying Cake Pressure Rise Tests... 

Differently from the approaches previously discussed, methods based on the pressure rise test are able to give information about the state of the whole system, that is, the temperature and the residual water content, and can thus be used in a control loop in addition, they also allow evaluation of the sublimation rate and, thus, the same considerations discussed above hold, even if the information can be obtained only at discrete times. Early works (Neumann, 1961, 1986 Nail and... 

Fissore, D., Pisano, R., Barresi, A. A., 2011a. On the methods based on the Pressure Rise Test for monitoring a freeze-drying process. Drying Technol. 29 73-90. 

Figure 7.5 provides a summary of recent analysis and experiments conducted at NASA GRC and WSTF for LCH4 work. In addition to engine testing, propellant tank conditions from the methane lunar surface thermal control (MLSTC) hoil off and pressure rise tests are plotted in Figure 7.5 (Plachta et al., 2012) along with previous low-pressure methane buhhle points (Jurns et al., 2007). The black line is the saturation curve for methane.

In the plant, this separation is accomplished with an isolation valve that separates the ice condenser from the drying chamber this valve is also able to permit (a) the pressure rise test at the end of the freeze drying cycle, (b) the simultaneous discharging and loading of the product and condenser defrosting, and (c) the reduction of cross-contamination between batches to a minimum. All the internal parts of the freeze dryer are of stainless steel type AISI 304L or 316L with a finished surface of 300 mesh or more. In the modern plants, the internal sterilization of the... 

Fig. 5.9 Comparison of (a) product temperature as estimated by pressure rise test technique and (b) chamber pressure profiles during primary drying for , solid line) uncontrolled and (O, dashed line) controlled...

Other dispersion evaluation methods include the pressure rise test, tape quality test and blown film test The pressure rise test involves extruding a given amount of plastics compound through a screen pack and monitoring pressure build-up as undispersed carbon black agglomerates and other contaminants plug the screen. For the tape quality test. 

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