11 of the disc 13 as a result of the projection the chamber 33 is formed with a downwardly opening annular portion 41 which encircles the projection extending vertically through the projection 40 is a threaded bore 42 whose upper end portion communicates with a fluid port 43 formed through the body 21 about midway between the ends thereof and communicating with the passage 22 an insert 44 is threaded into the bore and is formed with a small diameter inlet orifice 45 which meters liquid from the passage 22 and the port 43 to the chamber 33 and the upper side 11 of the disc 13 in carrying out the invention the body 21 and the housing 30 are formed with aligned ports 50 that define an excess liquid outlet which establishes communication between the chamber 33 and the passage 22 at a point downstream of the inlet port 43 an insert 51 is located in the passage 22 near the downstream end thereof and is sealed with respect to the passage by axially spaced o rings 52 a groove 53 formed circumferentially around the insert between the o rings establishes communication between the excess liquid ports 50 and a radial passageway 54 in the insert the passageway 54 also communicates with a relatively large diameter portion 55 of an axially extending passage 56 formed through the insert 51 the passage 56 being restricted by a small diameter orifice 57 located upstream of the passageway 54 with the foregoing arrangement liquid from the supply line 24 flows into the passage 22 and a portion of such liquid is metered into the chamber 33 and onto the disc 13 via the port 43 the.