Eyedroppers and Vacumatic plungers have valves, but pistons have no valves, why?

[Centurion]

Are the following statements true? … Vacumatic plungers like the Pilot Custom 823 need an exchange of air behind the ink thus need to open valve so ink can go down to the feed. With valve closed not enough air pressure to push ink down. On an ED like the Namiki Emperor you can open a valve to increase the air pressure behind the ink thus making it a wetter writer. But with a piston the all the air exchange is happening at the nib end and the feed.
 

Are piston feeds designed differently compared to ED pens or Vacumatic like the TSWBI plungers?

Edited September 28, 2024 by Centurion
Clarification

[effrafax]

Short answer: no, not really.  Longer answer: it's complicated.  [Not really.]  Once the valve is opened on a vacuum filler, there is no substantive difference between that and a piston filler.  Pen makers design their feeds to suit.

<Pedantic Pomme Alert>Your post comprises five sentences.  Of these, four are statements and one is a question.  Yet all five sentences end with a question mark.  WHY?  Personally, I find it irritating to read, as I'm constantly looking for the question that isn't asked.</Pedantic Pomme Alert>

[Centurion]

8 hours ago, effrafax said:

Short answer: no, not really.  Longer answer: it's complicated.  [Not really.]  Once the valve is opened on a vacuum filler, there is no substantive difference between that and a piston filler.  Pen makers design their feeds to suit.

<Pedantic Pomme Alert>Your post comprises five sentences.  Of these, four are statements and one is a question.  Yet all five sentences end with a question mark.  WHY?  Personally, I find it irritating to read, as I'm constantly looking for the question that isn't asked.</Pedantic Pomme Alert>

I edited my post for clarity. I didn’t know if my statements were true or not, that’s why I put a question mark. I guess the statements are true for the most part in a simplified sense, but not totally accurate?