Patent USPTO No. 2956845, drawing, page 1 (13), showing an axial piston pump, type swash plate, with spherical shaped piston heads and piston ring.
Gunnar A. Wahlmark, Rockford, Illinois USA.
Patent application, filed at USPTO May 9, 1956. Patent granted October 18, 1960
<a rel="nofollow" class="external text" href="http://patft.uspto.gov/netacgi/nph-Parser?Sect1=PTO2&amp;Sect2=HITOFF&amp;p=1&amp;u=%2Fnetahtml%2FPTO%2Fsearch-bool.html&amp;r=20&amp;f=G&amp;l=50&amp;co1=AND&amp;d=PALL&amp;s1=wahlmark.INNM.&amp;OS=IN/wahlmark&amp;RS=IN/wahlmark">Wahlmark patent US2956845, 1960, page 1</a>