Oh, ha. Thanks for the explanation. Yesterday, I understood the piston diagram, and I was scratching my head looking for the difference between the two. Good to

Oh, ha. Thanks for the explanation. Yesterday, I understood the piston diagram, and I was scratching my head looking for the difference between the two. Good to know I wasn't actually missing something. According to the plunger pump page, there is another practical difference - the pressure seal on the plunger pump is "stationary" allowing for higher pressure. Not sure why being stationary relative to the housing (but not relative to the plunger) makes the difference there.