ASME PTC 25:1998 pdf download Special Addenda to ASME PTC 25-1994 Pressure Relief Devices
4.7.7 Observation of Mechanical Characteris- tics. During the tests with superimposed or built- up back pressure, mechanical characteristics shall be observed by hearing, feeling, or seeing, and re- corded during the flow test. If the valve chatters, flutters, or does not reseat satisfactorily, such action shall be recorded. Upon agreement of all interested parties, the valve may be readjusted or repaired and retested. When testing valves against back pressure, any range in which the valve does not reach rated lift at the flow-rating pressure shall be recorded.
4.7.8 Recording Additional Data. It may be de- sirable or a requirement to record pressures other than, or in addition to, those listed in para.
4.3.4. Where possible, such recorded pressures shall be identified in accordance with Appendix I. With closed discharge systems, it is not possible to ob- serve or record some characteristic pressures.
4.8 TESTING WITH LIQUIDS, WITH BACK PRES- SURE ABOVE ATMOSPHERIC
4.8.1 Test Arrangements. Pressure sources can be a pump or an accumulator of liquid, in combination with high-pressure compressed gas. Precautions shall be taken to ensure that pressure pulsations are re- duced to a minimum. Figure 2 shows a recom- mended test arrangement, up to and including the test valve. Figures 5 and 6 show discharge arrange ments, for testing with superimposed and built-up back pressure, respectively. A flow meter [para.
4.2.4(bX7)] shall be used in either case. Instrumen- tation shall be suitably installed to indicate or re- cord the following:
(a) liquid temperature;
(b) flow-meter differential pressure; (c) valve-inlet pressure;
(d) back pressure.
4.8.2 Preliminary Tests. Preliminary tests may be permitted for testing and adjusting operation of the test apparatus and/or valve being tested (see para. 3.5). Such tests may be necessary to ensure the ab- sence of leaks in the test apparatus and to ensure that all gas or air has been vented from the com- ponent parts of the system.
4.8.3 Details of Procedure for Flow Measurement
(a) Atmospheric Back-Pressure Test. Tests may be conducted to determine the performance of the valve when discharging at atmospheric back pres- sure. The valve shall be equipped with an atmos- pheric discharge, as shown in Fig. 2. Test procedure shall be in accordance with paras. 4.5.3 (a) through (n), performing such portions of the procedure and recording such data as has been agreed upon. NOTE: The objectives of this portion of the test may be only to determine and record the set pressure and closing pressure of the valve; and the lift of the valve at the flow-rating pressure, when the valve is discharging to atmosphere. In this case, the portions of paras.
4.5.3
(a) through (h) relating to capacity determination may be eliminated.
(b) Back-Pressure Test. Following the atmos- pheric back-pressure test, if performed, install the discharge arrangement required by Fig. 5 or 6, d e pending on type of back pressure desired.
4.8.4 Testing With Superimposed Back Pressure [Fig. 5)
(a) Adjust the back pressure on the valve and discharge piping to the required value. Increase the pressure at the valve inlet. During the pressure in- terval starting at 90% of the expected set pressure, the rate of pressure increase shall not exceed 2.0 psilsec, or whatever lesser rate of increase is nec- essary for the accurate reading of the pressure. Observe and record the set pressure of the valve, the back pressure, and any other desired or pertinent characteristics.