Figure 8.14.1 shows a refrigeration compressor applied in automotive air conditioning systems. Such compressors are mass produced; the compressor casing is manufactured by casting. The compressors are to be subjected to gas tightness quality control. The gas tightness test must be carried out in a rapid, simple manner. The test is explained by means of Figure 8.14.2. Under normal conditions, the compressor transports the working fluid from the suction side (SS) to the pressure side (PS). During the gas tightness test, a nitrogen reservoir, equipped with a pressure regulator and a shut-off valve (Figure 8.14.3), is connected to the PS port of the compressor. (Nitrogen is selected as the working fluid due to its inertness.) 15 bar(rel) pressure is applied to the pressure port, i.e. it is attempted to "reversely blow" nitrogen through the compressor. The qm flow rate of nitrogen is measured downstream of the compressor, and the gas exhausts to the atmosphere. If the measured flow rate is below a defined threshold qm crit, the compressor under investigation is considered as "passed", i.e. it meets the gas tightness demands. If the measured flow rate exceeds the threshold, e.g. due to micro-ruptures, bubbles or inclusions, the sample is considered as faulty and is excluded from further processing. The test personnel can insert one compressor into the rig within seconds by means of fast connections (Figure 8.14.4). A variable area flowmeter (rotameter) is applied for flow rate measurement. The rotameter can be read easily and quickly by simple ocular inspection, and the required flow rate threshold can be clearly marked on the flowmeter. This implies that there is no need of specially trained personnel for the gas tightness test. The appropriateness of e.g. 4 compressors per minute can be judged. Figure 8.14.5 presents the full assembly of the test rig.