1880 II. 616 The same plan of cushioning is also applied to the sub-pistons which operate the valve.
1900 G. D. Hiscox 66 When the ports in the sub-piston close.
2001 41 422/1 (caption) Superfluid shock test tube facility: (1) MO-main valve; (2) high-pressure chamber; (3) sub-piston; (4) main-piston.