Abstract: Method and apparatus are provided for transferring particles from an upper zone through an intermediate zone to a lower zone. A valveless conduit provides particle communication from the upper zone to the middle zone and a valved conduit provides particle communication from the middle zone to the lower zone. The transfer of particles between the zones through the conduits is regulated by varying the pressure of the middle zone, the flow rate of gas passing through the valveless conduit, and the valve in the valved conduit.

Abstract: A pressure control system for accurately controlling the pressure of the air in a discharge line during a pneumatic offload includes a blower, a supply of pressurized air and a pressure relief valve. The blower directs a stream of air into the discharge line to produce a positive air pressure. The pressure relief valve includes a valve body defining a hollow valve chamber, a valve positioned within the valve chamber and a valve seat opposite the valve. The valve chamber of the pressure relief valve is in fluid communication with the discharge line through a first inlet port and in fluid communication with the supply of pressurized air through a second inlet port that receives air from the supply of pressurized air. The valve chamber of the pressure relief valve is also in fluid communication with the ambient atmosphere through at least one outlet port.