PURPOSE: To obtain the title device capable of installing DDR without giving restriction to relationship of position among raw material chest, pump and DDR by re-circulating excess raw material by air pressurizing device.

CONSTITUTION: Raw material inlet of DDR 5 is connected to the outlet using a circulating line and excess raw material is circulated through a pressurizing box 13. Level control of pressurizing box 13 is carried out by action of control valve 19 for air blow opened and closed by signal of pressure air having pressure higher than head pressure +0.3kg/cm2 of pump 2 from a pressure air feed device 14. Air pressure is controlled by pressure controller 16 and pressure control valve 17 and pressure in pressure box 13 is controlled by the control valve 19. Thereby change of pressure in the system is absorbed to stabilize the device 14.