Shotcrete gun

A concrete spraying machine comprising--

• a) a feed hopper (12) for receiving a dry concrete mixture;
• b) an outlet pipe (15) having a compressed air connector (16) for connection to a compressed air source;
• and
• c) a motor-driven multi-chamber drum rotor (4) rotatable about a vertical axis and having upper and lower surfaces and at least three chambers, the drum rotor being located between an outlet from the hopper (12) via which the dry concrete mixture can enter the chambers and the outlet pipe (15) through which the dry concrete mixture leaves the chambers, the upper surface of the drum rotor adjoining a gasket (11), (hereinafter defined as the upper gasket) having one or more openings and being fixed to a clamping plate (10), and the lower surface of the drum rotor adjoining a gasket (9) (hereinafter defined as the lower gasket, which is fixed to a base plate (1), each of said chambers having openings capable of communicating with both the hopper (12) and the outlet pipe (15) but the arrangement being such that one of said chambers cannot communicate with both at the same time, the clamping plate containing a compressed air connector (17) for blowing the dry mixture out of the chambers and into the outlet pipe (15), and a compressed air release opening (6) for allowing compressed air to escape from the chambers (29), the opening being located, in drum rotation sequence, between a position where a said chambers communicate with the outlet pipe (15) and a position where said chambers communicate with the hopper outlet;
• characterized by a connection (11c) in the upper or lower gasket which connects at least one of said chambers (28) empty of said concrete mixture with at least one of said chambers (25) containing said concrete mixture to allow an equalizing of the pressure between the chambers.