ASME PTC 25:1998 pdf download

ASME PTC 25:1998 pdf download Special Addenda to ASME PTC 25-1994 Pressure Relief Devices
4.7.7Observation of Mechanical Characteris-tics.During the tests with superimposed or built-up back pressure, mechanical characteristics shallbe observed by hearing, feeling, or seeing, and re-corded during the flow test. If the valve chatters,flutters, or does not reseat satisfactorily, such actionshall be recorded.Upon agreement of all interestedparties, the valve may be readjusted or repaired andretested. When testing valves against back pressure,any range in which the valve does not reach ratedlift at the flow-rating pressure shall be recorded.
4.7.8Recording Additional Data.lt may be de-sirable or a requirement to record pressures otherthan, or in addition to, those listed in para. 4.3.4.Where possible, such recorded pressures shall beidentified in accordance with Appendix I. Withclosed discharge systems, it is not possible to ob-serve or record some characteristic pressures.
4.8TESTING wITH LIQuIDs, WITH BACK PRES
SURE ABOVE ATMOSPHERIC
4.8.1Test Arrangements. Pressure sources can bea pump or an accumulator of liquid, in combinationwith high-pressure compressed gas.Precautions shallbe taken to ensure that pressure pulsations are re-duced to a minimum. Figure 2 shows a recom-mended test arrangement,up to and including thetest valve. Figures 5 and 6 show discharge arrange-ments,for testing with superimposed and built-upback pressure,respectively. A flow meter [para.4.2.4(bXT) shall be used in either case. instrumen-tation shall be suitably installed to indicate or re-cord the following:
(a liquid temperature;
(flow-meter differential pressure;ic)valve-inlet pressure;
(dback pressure.
4.8.2Preliminary Tests. Preliminary tests may bepermitted for testing and adjusting operation of thetest 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 ensurethat all gas or air has been vented from the com-ponent parts of the system.
4.8.3Details of Procedure for Flow Measurement(a)Atmospheric Back-Pressure Test. Tests maybe 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. Ob- serve and record the set pressure of the valve, the back pressure, and any other desired or pertinent characteristics. (b) Continue increasing the pressure at the valve inlet until the valve remains open. Observe the ac- tion of the valve. Gradually decrease the inlet pres- sure until the valve closes. Record the reseating pressure of the valve and the back pressure. Observe the action of the valve.