A spiral flow constant pressure pump comprises pump body (11), a pump casing (10) and an impeller (1). By using a pressure drop between an end surface of a pump rear cover (3) and a back end surface of an auxiliary blade (1-2) of the impeller, washing water is provided for a sealing device (6). A water inflow slant hole (5) is disposed at a high-pressure area of the end surface of the pump rear cover (3), a location where the water inflow slant hole (5) enters a sealing cavity (4) is close to the sealing device (6), and quasi-high-pressure water is introduced into the sealing cavity (4). A water outflow slant hole (8) is disposed at a low-pressure area of the end surface of the pump rear cover (3), and a location where the water outflow slant hole (8) leaves the sealing cavity (4) is far away from the sealing device (6). After washing the sealing device (6), the quasi-high-pressure water entering the sealing cavity (4) passes through the water outflow slant hole (8) along the flowing direction, and flows forward back to the low-pressure area. The pump recovers some energy, water force efficiency of the pump is improved, turbulence loss is reduced, and moreover, friction heat and gas which possibly exists in the sealing cavity (4) are taken away; a lengthened throttling bush (2) reduces damage of the high-pressure water leaked from the sealing cavity (4) to the pressure drop of the auxiliary blade (1-2), and ensures the balancing effect of the auxiliary blade (1-2).
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