requires the air supply at a different stage in the process the valve in the discharge hose 210 is opened and the mixture is discharged via the discharge outlet 200 and is conveyed along discharge hose 210 to its required location a conventional tripod arrangement 220 may be provided to kill the energy in the mixture concrete and allow it to fall in a heap to be spread as can be seen in fig5 the mixing vessel 140 is generally of spherical configuration the pressure shell 141 forming the outer part of the mixing vessel 140 is formed from a pair of hemispheres produced by pressing or spinning the shell is provided with 12 lining segments 142 these sufficiently duplicate the form of the pressure shell 141 which they protect from abrasive wear of the constituents to be mixed within the vessel eight of the lining segments 142 are reversible top to bottom the charging inlet 143 is provided at the top of the vessel 140 and the discharge outlet 200 is provided slightly offset from the bottom of the vessel 140 as can be seen in fig6 a and 6 b the charging inlet of the mixing vessel 140 is provided with a lid 210 to seal the vessel water is admitted by a branch formed in the lid housing 211 it passes through a hole in a flat seal 212 and thence to a nozzle formed in the seal retaining place 213 a non return valve not shown prevents reverse flow through the branch when the vessel 140 is pressurised the seal plate 213 and the housing 211 are formed to dish the seal the shape of the seal plate 213 and housing 211.