PURPOSE:To permit an exact amount of chemical to be supplied free from the influences of the pressure dependent upon the depth of chemical and siphonage caused by a second pipe by providing a third pipe with one end open extending from the second pipe for supplying chemical from a constant discharge pump to a processing tank to a higher position than the chemical surface in a chemical dissolved water storage tank. CONSTITUTION:When discharging a predetermined amount of chemical 7 from a chemical dissolved water storage tank 1 by a constant discharge pump 2, the chemical is temporarily raised from a second pipe 4 into a third pipe 5 by the pump pressure. Ae the chemical flows out into a processing tank 6, however, it is lowered escaping from the third pipe 5 and standing near a connection B thereof. For this reason, the pressure exerted on the constant discharge pump 2 dependent upon the depth of the chemical 7 is approximately balanced by chemical 7A in the second pipe 4 and siphonage at the end of the second pipe 4 is eliminated by the entry of air from the third pipe 5. Therefore, there is no chemical passing through the constant pressure pump 2 after termination of the pump action, thereby making the discharge amount constant.
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