fig1 illustrates a typical &# 34 ; semi - nozzle &# 34 ; pilot operated safety - relief valve 10 in accordance with the teachings of the prior art . valve 10 includes a valve body 12 having an outlet 14 and a cover plate 16 . the nozzle portion of valve 10 is formed by the lower portion 17 of valve body 12 and a seat ring 18 which is mechanically connected to portion 17 of valve body 12 . a pitot or &# 34 ; dipper &# 34 ; tube 20 is inserted within an opening 22 in portion 17 of valve body 12 . a sensing line 24 is coupled to a pilot control ( not shown ) which operates the control mechanism for a piston 26 which is slidably displaceable within a cylinder 28 to seal the mouth 30 of the nozzle formed by seat ring 18 . as can be seen , the pressure sensing device is directly inserted in an opening within the nozzle formed in portion 17 of valve body 12 . fig2 illustrates a typical &# 34 ; full nozzle &# 34 ; pilot operated safety - relief valve 32 in accordance with the teachings of the prior art and in which like reference numerals have been utilized to refer to like structure shown in fig1 . as can be seen in the design , a full nozzle portion 34 is threaded to valve body 12 and no seat ring is utilized in the design . since nozzle 34 is completely separate from valve body 12 , there is no pressure tap located within valve body 10 . instead , an accessory collar 36 , which sits between the valve and the pressure vessel , is utilized . the pressure sensing device 20 is disposed in an opening 38 in collar 36 . collar 36 is then mechanically coupled between valve 32 and the pressure vessel ( not shown ). fig3 illustrates a safety pressure relief valve 40 constructed in accordance with the present invention . valve 40 includes a valve body 42 having a mechanically coupled cover plate 44 and an exhaust opening 46 . the lower portion 48 of valve body 42 includes an internally threaded inlet opening 50 for receiving a full nozzle 52 . nozzle 52 has external threads 54 for engaging opening 50 in lower portion 48 of valve body 42 . the throat 56 of nozzle 52 is engaged and sealed by a piston 58 slidably disposed in a cylinder 60 . also disposed within cylinder 60 is a spring 62 for biasing piston 58 into engagement with throat 56 of nozzle 52 . cylinder 60 is threaded to cover plate 44 and includes an opening 64 , to which is coupled a control line 66 which is connected to a pilot control 68 . fluid flows between pilot control 68 and cylinder 60 through line 66 to operate piston 58 . pilot control 68 will , when the pressure of the pressure vessel ( not shown ) is within preset parameters , bias piston 58 against mouth 56 of nozzle 52 , thus maintaining the pressure within the pressure vessel . when the pressure sensed by the pilot control 68 is above the preset parameters , it will reduce the pressure in control line 66 to permit piston 58 to be displaced away from mouth 56 of nozzle 52 , releasing the pressure from the pressure vessel . the released pressure flows through nozzle 52 , valve body 42 and is exhausted through outlet 46 . the details of the construction of pilot control 68 and piston 58 have been omitted since they are known to those skilled in the art and do not form part of the present invention . attention should now be given to fig4 in addition to fig3 . fig4 illustrates in detail the interface between nozzle 52 and lower portion 48 of valve body 42 . the lowermost part of nozzle 52 includes a flange 70 which is disposed along the underside of the lower flange 72 of valve body 42 . a cylindrical surface 74 surrounding the lower periphery of nozzle 52 is generally perpendicular to flange 70 of nozzle 52 . surface 74 has a diameter slightly greater than that of threading 54 on nozzle 52 . an annular recess 76 is disposed in surface 74 . flange 72 of valve body 42 also includes a cylindrical surface 78 which is contiguous with surface 76 of nozzle 52 . an annular recess 80 is disposed in surface 78 so that recesses 80 and 76 form an annular port 82 surrounding the periphery of the interface between nozzle 512 and portion 48 of valve body 42 . an upper circumferential seal 84 and a lower circumferential seal 86 are located between opposed surfaces 74 and 78 to maintain a pressure seal around port 82 to maintain port 82 at the same pressure as the interior of nozzle 52 . seals 84 , 86 may be in the form of o - rings or other suitable seals and may be constructed of elastomeric , plastic or metallic materials . while annular port 82 has been shown as being disposed both in nozzle 52 and portion 48 of valve body 42 , it is to be noted that port 82 may alternately be formed entirely in either nozzle 52 or valve body 42 . the configuration of port 82 is not critical , it is only necessary that it not restrict the transmission of pressure from nozzle 52 . the materials used in the construction of valve 40 may be identical to those used in prior configurations . an opening 88 leading to the interior of nozzle 52 is disposed in recess 76 in nozzle 52 . a pitot or dipper tube 90 having a shaft 92 and a head 94 is placed within opening 88 . pitot tube 90 is of standard configuration and includes an opening 96 exposed to pressure within nozzle 52 and an interior channel 98 for communicating the pressure within the interior of nozzle 52 to port 82 . a channel 100 , including a tapped port 102 , is formed within flange 72 of valve body 42 . channel 100 communicates the fluid pressure within annular port 82 to a pressure sensing line 104 which in turn is connected to pilot control 68 . the pressure within nozzle 52 is communicated through pitot tube 90 to port 82 . thereafter , the pressure within port 82 is communicated through channel 100 in flange 72 of valve body 42 to line 104 which in turn is transmitted to pilot control 68 . thus , there is no mechanical connection between pitot tube 90 and pilot control line 104 . rather , both communicate with annular port 82 . this permits pitot tube 90 and nozzle 52 to be rotated to any angular position with respect to channel 100 and valve body 42 without in any way disturbing the pressure measurements . differences in position between nozzle 52 and valve body 42 may occur due to wear and disassembly ; however , in the arrangement illustrated such differences are to no effect . the pressure sensing apparatus will operate as effectively when nozzle 52 is rotated so that pitot tube 90 is 180 degrees apart from channel 100 in valve body 42 as shown in fig3 as when both are at the same angular position as shown in fig4 . fig5 illustrates another embodiment of the invention which permits the direct injection of purging material into the interior of the nozzle to prevent clogging of the nozzle and valve . in this embodiment like reference numerals have been used to illustrate like structure to that previously described . in this embodiment a valve 110 has an annular port 112 located at the nozzle / valve body interface . the construction of port 112 is in all respects identical to that of annular port 82 previously described . the difference in structure is the inclusion of a series of channels 114 which lead to injection ports or openings 116 permitting fluid communication between annular port 112 and the interior of nozzle 52 . channels 114 are disposed at a generally downward angle θ so that the purging fluid will direct the removed clogging material away from the nozzle . injection ports 116 are preferably equi - angularly spaced about the inner periphery of nozzle 52 . angle θ and the number of injection ports 116 are selected from empirical measurements as a function of the difficulty of removing the clogging material . the position of channels 114 and injection ports 116 is preferably situated relatively close to the mouth of nozzle 52 so as to assure against clogging within the entire length of nozzle 52 . in operation , high pressure steam or other purging material will be injected from a line attached to port 102 through channel 100 in flange 72 of valve body 42 and will pass into annular port 112 and thereafter through channels 114 to injection ports 116 to dislodge the clogging material . the steam , compressed air or other purging material is supplied by a pressure source 118 . coupled to pressure source 116 is a pressure measuring device 120 which may be of any of the usual types to measure the pressure delivered to valve 110 . the pressure measurement may be used to detect a nozzle which is in the process of becoming clogged or plugged . when the purging material is injected , the greater the amount of pressure required to unplug the nozzle , the greater degree of plugging of the nozzle . when the pressure of the injected purging material drops to the level , previously measured , of a clean nozzle assembly , assurance will be had that the nozzle has been completely unplugged . the use of annular port 112 to permit the injection of purging material into the nozzle is not limited to pilot operated valves but may also be used with respect to other safety relief valves such as the usual type of spring - loaded &# 34 ; pop - off &# 34 ; valves . again , as in the previous embodiment , the angular position of nozzle 52 with respect to valve body 42 is unimportant since annular port 112 assures fluid communication between the external source of pressure and the interior of the nozzle . thus any wear of the threading causing the nozzle to seat at a different rotational position with respect to the valve body will not in any way effect the operation or unclogging og the valves . although the present invention has been described in conjunction with preferred embodiments , it is to be understood that modifications and variations may be resorted to without departing from the spirit and scope of the invention , as those skilled in the art will readily understand . such modifications and variations are considered to be within the purview and scope of the invention and the appended claims .