Safety devices

50 atmosphere. For this reason, during relief, a gas leak occurs through this orifice. Utilized material: EN 12420-CW617N brass. Disc: obtained through bar machining and equipped with gasket, it ensures the required sealing degree on the valve seat. The gasket is made in P.T.F.E. (Polytetrafluorethylene), a material that, during valve estimated service life, maintains a good strength and does not cause the disc to stick on the seat. The disc is properly guided in the body and the guide action can never fail; there are no glands or retaining rings that hamper the movement thereof. Utilized material:...

51 L H1 H2 D H3 Ch safety devices such as safety valves. Such devices shall prevent pressure from permanently exceeding the max allowable pressure PS of the equipment they protect. In any case, a short pressure peak limited to 10% of admissible maximum pressure is permitted. As to the selection and sizing of the suitable protection device, users shall refer to the specific sector or product standards. EN 378-2: 2008 Standard “Refrigerating systems and heat pumps – safety and environmental requirements – Part 2: Design, construction, testing, marking and documentation”, harmonized with 97/23/EC...

52 for this calculation the value of k shall be as measured at 25 °C. (Section 7.2.3, Standard EN 13136: 2001/A1:2005). Values of k and calculated values of C for some refrigerants are given in table A.1 of the aforesaid standard. Following we show the values of k and C for the more useful refrigerants. SIZING OF SAFETY VALVES DESIGNED TO DISCHARGE GAS OR VAPOUR AT CRITICAL FLOW (Ref. EN 13136: 2001/A1: 2005) Critical flow occurs when the backpressure pb (the pressure existing immediately at the outlet of a safety valve) is below or equal to the critical pressure: [bar abs] with: – po = actual...

53 – çv = volumetric efficiency estimated at suction pressure and discharge pressure equivalent to the safety valve setting. with: – V = theoretical displacement of compressor [m3] – n = rotational frequency of compressor [min –1] – ñ10 = vapour density at refrigerant saturation pressure / dew point at 10 °C [kg/m3] These conditions, settled in any case by the designer, are considered the most unfavorable for the safety valve in consequence of functional defects as: – move mistake; – non-working of automatic safety devices, set to operate before safety valve. It shall be excluded: – closeness...

54 Sizing of minimum flow area of the safety valve [mm2] with: – C = 2,51, corresponding to isentropic exponent k for R407C equal to 1,14, according to table A1 of standard EN 13136:2001/A1:2005; – Kd = 0,83, certified coefficient of discharge for safety valve 3030/88; – vo = 0,0104 [m3/kg], specific volume of overheating vapour upstream the safety valve during relieving. This value is referred to the following operating conditions, upstream the safety valve: – pressure po = 27,25 [bar abs]; – temperature To = 100 [°C] (precautionary temperature, settled in any case by the designer). Conclusion:...

55 with: – A = flow area of safety valve [mm2]; – Ain = inside area of inlet tube to valve [mm2]; – Kdr = Kd x 0,9, derated coefficient of discharge; – C = function of isentropic coefficient k; – î = addition of pressure loss coefficients în of any component and piping; The coefficients în are relevant to: – pipe elements loss, as connections and bends; – valves loss; – loss along the pipe and are listed in EN 13136:2001/A1:2005 Standard, Table A.4. Example: assume to install, on the condenser of the previous example, a safety valve type 3030/88, set to 25 bar, using a steel union with the following...

56 Example: assume to install a discharge pipe on safety valve type 3030/88 of the previous example, using a steel tube nominal size 2” with the following characteristics: - dout = 53 [mm] , inside diameter - Aout = 2206 [mm2] , inside area - L = 3000 [mm] , length - pipe bend 90° with bending radius R equal to three times external diameter of tube From table A.4 it’s possible to have these data: - î1 (bend) = 0,25 - î2 (length) = ë x L/ din = 0,02 î 3000/53 = 1,13 with ë = 0,02 for steel tube - îT = î1 + î2 = 0,25 + 1,13 = 1,38 Pressure loss in the downstream line is: The obtained value is admissible...

57 SAFETY VALVES 3060 GENERAL DESCRIPTION Valves series 3060 are safety devices according to the definition given in Article 1, Point 2.1.3, 2nd dash of 97/23/EC Directive and are the subject of Article 3, Point 1.4 of aforesaid Directive. The valves above mentioned are standard type, unbalanced, direct-loaded safety valves. Valve opening is produced by the thrust the fluid under pressure exerts on the disc, when said thrust exceeds, under setting conditions, the opposing force of the spring acting on the disc. Valves are identified by means of: – a model number formed of an alphanumerical coding...

SCOPE Use: protection against possible overpressures of the apparatuses listed below, with regard to the operating conditions for which they have been designed: – refrigerating system and heat pump components, for instance: condensers, liquid receivers, evaporators, liquid accumulators, positive displacement compressor discharge, heat exchangers, oil separators, piping. (reference: EN 378-2: 2008); – simple pressure vessels (reference: 87/404/ EEC Directive). Fluids: the valves can be used with: • refrigerant fluids, in the physical state of gas or vapour, belonging to Group II according to the...

59 Ch H1 L H2 H3 ØD for calculation” highlights the possible causes of overpressure in a system and makes available to users the instruments for pressure relief device sizing, among which the safety valves. For sizing and installation of safety valves series 3060 see the previous chapter of safety valves series 3030. TABLE 4: Dimensions and Weights of valves 3060 Catalogue number Weight [g] 3060 Ø D L Ch H1 H2 H3 21,5 21,5 21,5 21,5 24,5 30 30 35 35 35 35 39,0 40 40 20 20 20 20 23 27 27 33,5 33,5 33,5 33,5 37 37 40 46,5 46,5 46,5 46,5 52,5 59,5 59,5 80 80 80 80 89 96,5 99,5 180 195 195 195 240...