One of my customers had a RFQ for a Check valve, and wasn't sure if her customer was wanting a Piston or Swing. I tried to explain to her the difference in a piston check valve and a swing check valve and here is what I came up with.
My expert engineer explained that the clapper in the swing check valve, is attached to a hinge pin, and swings freely, so when pressure is being applied, it takes very, very, very minimal pressure to make the clapper move.
In a Piston Check – it takes more pressure because the movement is up and down. (Movement is vertical) – And is harder for the air to go through.