self-lapping en · ADJ
Etymology
From self- + lapping.
Meanings
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(not-comparable) Of a valve, especially for brakes, maintaining the force of pressure selected by a control.
Thus, in the newer locomotives for the Great Northern line, the Woodward governors are adapted for air (not solenoid) control and continuous engine speed control through a self-lapping valve replaces the individual-speed steps, allowing operation in multiple with English Electric and Birmingham diesels.
1961 February, R. K. Evans, “The role of research on British Railways”, in Trains Illustrated, page 95:[...] Mr. Grierson remarks that on the L.P.T.B. tube stock in general the electro-pneumatic brake is in use, but that the new 1938 stock is fitted with the self-lapping electro-pneumatic brake, which is under the control of an automatic mercury-operated retardation controller when normal service stops are being made.
1944 May and June, “Notes and News: Bakerloo Tube Stock”, in Railway Magazine, page 184: