Birkett Technical Catalogue - Safety Systems UK Ltd

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POP ACTION - TYPE 2 PILOT Pilot construction The pilot is essentially a spring loaded safety valve with blowdown adjustment which, during its operation, positions itself on one of two seats. The upper drain seat is used to determine pilot set pressure, the lower feeding seat determines pilot blowdown. The valve disc is held on the soft upper drain seat by the setting spring, which also determines the pilot set pressure. This valve disc is connected via a spindle to the lower feeding seat, which controls the system flow into the dome and which also controls the pilot blowdown. TO AND FROM MAIN VALVE DOME FEEDING SETTING SPRING DISC UPPER DRAIN SEAT EXHAUST SPINDLE The valve disc and lower feeding seat move together; this action opens and closes each respective seat, thereby allowing the pilot to control the operation of the main valve during the relieving cycle. LOWER FEEDING SEAT FILTER Pilot operation With pop action pilot operation, the main valve is either in the fully open or shut position. The operation is characterised by a distinct rapid “pop” action, which is evident at the opening of the main valve, followed by a positive re-seat action when the main valve closes. The re-seat pressure of the Type 2 pilot valve is adjustable externally, independently of the set pressure adjustment. This graph demonstrates pop action. When set pressure is reached, the pilot valve opens rapidly; this action de-pressurises the dome volume very quickly and the main valve opens. This is shown by the vertical (rising) line on the graph, illustrating that the main valve achieves its design lift at set pressure. The re-seating characteristic is equally positive: when the system pressure has fallen to the pre-set pilot re-seat pressure, the pilot drain seat closes rapidly. This action allows the dome to be repressurised very quickly, thereby closing the main valve completely. This is shown on the graph by the vertical (falling) line. 63
STAGES OF OPERATION - TYPE 2 PILOT Stage 1 System pressure below the pilot set pressure, dome pressurised, main valve closed. Stage 2 System pressure equal to set pressure, drain seat opens, dome de-pressurises, main valve fully lifts with no overpressure. Stage 3 System pressure equal to or greater than set pressure, dome pressure is atmospheric, main valve is fully open. Stage 4 System pressure falls to equal the re-seat pressure, drain seat closes, feeding seat opens, dome is pressurised, main valve closes. Stage 5 System pressure below the pilot set pressure, dome pressurised, main valve closed and ready for next upset condition. Key Points – Pilot Type 2 • Pilot set pressure = Main valve set pressure. • Main valve fully open at 0% overpressure. • The pilot is non flowing. • Adjustable blow-down feature. • Integral filter fitted. • Gas duty only. 64
Page 1 and 2:
Pressure & Flame Protection Safety
Page 3 and 4:
CONTENTS Page Birkett Range 3 Intro
Page 5 and 6:
INTERNATIONAL APPROVALS AND AUTHORI
Page 7 and 8:
FEATURES AND BENEFITS Design verifi
Page 9 and 10:
THE EFFECT OF BACK PRESSURE The con
Page 11 and 12:
LIFT CYCLE Stage 1 - Closed Inlet p
Page 13 and 14: WB 300 - BALANCED BELLOWS GAS TYPE
Page 15 and 16: WB 300 - BALANCED BELLOWS GAS TYPE
Page 17 and 18: FERRULE Ferrule (government ring) A
Page 19 and 20: RECOMMENDED MATERIAL TEMPERATURE RA
Page 21 and 22: VALVE SELECTION TABLE D - 0.110 in
Page 23 and 24: VALVE SELECTION TABLE E - 0.196 in
Page 25 and 26: VALVE SELECTION TABLE F - 0.307 in
Page 27 and 28: VALVE SELECTION TABLE G - 0.503 in
Page 29 and 30: VALVE SELECTION TABLE H - 0.785 in
Page 31 and 32: VALVE SELECTION TABLE - 1.287 in 2
Page 33 and 34: VALVE SELECTION TABLE K - 1.838 in
Page 35 and 36: VALVE SELECTION TABLE L - 2.853 in
Page 37 and 38: VALVE SELECTION TABLE M - 3.60 in 2
Page 39 and 40: VALVE SELECTION TABLE N - 4.34 ins
Page 41 and 42: VALVE SELECTION TABLE P - 6.38 ins
Page 43 and 44: VALVE SELECTION TABLE Q - 11.05 in
Page 45 and 46: VALVE SELECTION TABLE R - 16.00 in
Page 47 and 48: VALVE SELECTION TABLE T - 26.00 in
Page 49 and 50: BLOWDOWN RING SETTING The blowdown
Page 51 and 52: SEAT TIGHTNESS / SEAT LEAKAGE TESTI
Page 53 and 54: FEATURES AND BENEFITS Design verifi
Page 55 and 56: D SERIES THERMAL RELIEF VALVES ITEM
Page 57 and 58: SAFEFLO - SAFETY AND THERMAL RELIEF
Page 59 and 60: D SERIES DIMENSIONS Female screwed
Page 61 and 62: FEATURES AND BENEFITS Close system
Page 63: MODE OF OPERATION Safeset consists
Page 67 and 68: MODULATING ACTION - TYPE 8 The Type
Page 69 and 70: STAGE 4 System pressure above set p
Page 71 and 72: MATERIALS OF CONSTRUCTION - MAIN VA
Page 73 and 74: ACCESSORIES Back flow preventer Hig
Page 75 and 76: ACCESSORIES Others Similar to the s
Page 77 and 78: SAFESET PILOT FIGURE NUMBERING SYST
Page 79 and 80: Size Orifice Rating A (ins) D (ins)
Page 81 and 82: FLANGE PRESSURE / TEMPERATURE LIMIT
Page 83 and 84: (4) Constant, Fb Fb = 2k k-1 Pb P k
Page 85 and 86: BACKPRESSURE AND BLOWDOWN LIMITS Fi
Page 87 and 88: Table 3 Representative data on liqu
Page 89 and 90: Graph 4.0 Factor Fl - For applicati
Page 91 and 92: Pressure Protection 90
Page 93 and 94: SATURATED STEAM CAPACITY CHART WB 4
Page 95 and 96: AIR CAPACITY CHART Pilot:Types 2, 4
Page 97 and 98: DUAL OUTLET / FULL BORE PILOT VALVE
Page 99 and 100: DEFINITION OF TERMS Pressure Relief
Page 101 and 102: PRESSURE TERM RELATIONSHIP Pressure
Page 103 and 104: SAFETY RELIEF VALVES B/C Series D S
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Birkett Technical Catalogue - Safety Systems UK Ltd

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