The invention provides a spiral flow constant pressure pump, comprising a pump body, a pump casing and an impeller; the pressure drop between the end face of pump rear cover and the rear end face of impeller auxiliary blade is used for providing wash water to sealing device; a hole is opened in the high pressure area of the end face of pump rear cover; the position of the hole for entering the seal cavity is close to the sealing device, leading expectant high pressure water into the seal cavity; a hole is opened in the low pressure area of the end face of pump rear cover; the position of the hole for exiting the seal cavity is far away from the sealing device; the expectant high pressure water that enters the seal cavity will flow back to low pressure area through the drainage hole along flow direction after washing the sealing device; the pump recycles a part of energy, improves the hydraulic efficiency, decreases the turbulent loss and takes way the gas might exist in the seal cavity; the extended orifice sleeve reduces the damage to the pressure drop of the auxiliary blade caused by the high pressure water leaked from seal cavity and thus ensures the balance effect of the auxiliary blade.
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