PURPOSE: To unnecessitate the fitting of an external water-injecting pipe by removably fitting an orifice in a communicating hole between a pressure chamber of the pump and a gland packing section.

CONSTITUTION: Pressurized water in the pressure chamber 13 is restricted in flow rate by the orifice 15 and flows through grooves on the inside and outside peripheral surfaces of a seal ring 10 to the lateral surface of the gland packing 9, where it presses the packing 9 against the inside surfaces of packing glands 11, 12. By the pressing action, the packing is extended along the inside and outside peripheral surfaces, increasing the adhesion to a sleeve 6 and a side cover 8. The rate of flow through the orifice 15 can be regulated by replacing the orifice with other one having a different orifice hole diameter.