into a solid mass in still other embodiments the plug 96 can be formed in a separate mold and then inserted into sleeve 94 it is desirable to coat the inside of sleeve 94 with a sealant such as an adhesive to prevent leaks between plug 96 and sleeve 94 plug 96 can be made of any one of a variety of soluble substances such as aspirin sugar salt etc that can dissolve in water and thereby release the pressure inside line 46 for embodiments that are designed to respond to fluids other than water plug 96 will be chosen to be soluble in that other fluid in some embodiments sleeve 94 may be eliminated and plug 96 may be made with a diameter that allows plug 96 to be snugly inserted into pressure line 46 in order to close and seal the pressure line 46 referring to fig9 pressure line 46 u2032 is modified to have external threads on its distal end an alternate sleeve 98 is internally threaded at its proximal end to receive line 46 u2032 sleeve 98 has on its distal end an inwardly diverging throat 100 that is preferably frustoconical a frustoconically shaped soluble plug 102 is sealingly fitted in frustoconical throat 100 plug 102 may be formed in a manner similar to that previously described in connection with fig8 since plug 102 and throat 100 are similarly tapered pressure applied from line 46 u2032 will tend to press plug 102 outwardly which will tend to wedge the plug.