4 ms·

That diagram at the top of the Wikipedia article made the concept more clear to me than the whole orginal post. Drawing the valves like that really helps. Edit

by maym86 8y ago

That diagram at the top of the Wikipedia article made the concept more clear to me than the whole orginal post. Drawing the valves like that really helps. Edit: grammar

alanbernstein 8y ago
That's funny, I don't know what that diagram is trying to convey.
- barrkel 8y ago
  I suspect it might have something to do with your mechanical aptitude - the mechanism is suggested by the shapes of the parts. The diagram is reminiscent of those tests we did in school to help choose a career.
- Stratoscope 8y ago
  Your confusion is understandable, since the Wikipedia article doesn't even make the slightest attempt to explain the diagram. So let me try. Let's start with the piston pump on the left. The brown piece moves up or down in a tube, and the two black "T" figures are valves that open or close in response to water pressure. The down arrow next to the piston indicates that the piston is currently moving down and pushing on the water. This causes the valve at the bottom to close and the valve on the left to open. So water comes out at the top left. After the piston is pushed down as far as it will go, you start pulling the piston back up. This is not shown in the diagram, but now everything is reversed. The valve at the left closes, and the valve at the bottom opens, both in response to the pressure change. So now, water is pulled up from the well or other source, filling the chamber. When it is full, you start pushing down again, and the cycle begins anew: the valve on the left opens and the valve on the bottom closes, pushing water out of the spout at the top left. Once that makes sense, take a look at the plunger pump on the right side of the diagram. You will see that it works on exactly the same principle: when you move the brown part up or down, it pulls or pushes on the water in the same way as the piston pump. The only difference is in the shape of the moving part.
  - simongr3dal 8y ago
    The most recent AvE video had a break down of a pressure washer which includes an explanation of a piston pump. https://youtu.be/4IbjQyR9X6E https://youtu.be/4IbjQyR9X6E
  - lucb1e 8y ago
    > Your confusion is understandable, since the Wikipedia article doesn't even make the slightest attempt to explain the diagram. A little meta, but in these situations I usually try to improve the source and post a reply saying I edited it, instead of explaining it to one (or a few) person(s) here. Not saying it was bad that you just wrote a big comment explaining it completely! Just an idea of equal effort while reaching more people :)
    - Stratoscope 8y ago
      That's very good advice, thanks for the reminder. I do edit Wikipedia fairly often, but didn't feel like I had enough time to do a creditable job on this topic this weekend. So consider my HN comment a rough draft of an upcoming Wikipedia edit.
  - alanbernstein 8y ago
    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.

by maym86 8y ago

That diagram at the top of the Wikipedia article made the concept more clear to me than the whole orginal post. Drawing the valves like that really helps. Edit: grammar

alanbernstein 8y ago

That's funny, I don't know what that diagram is trying to convey.

barrkel 8y ago
I suspect it might have something to do with your mechanical aptitude - the mechanism is suggested by the shapes of the parts. The diagram is reminiscent of those tests we did in school to help choose a career.
Stratoscope 8y ago
Your confusion is understandable, since the Wikipedia article doesn't even make the slightest attempt to explain the diagram. So let me try. Let's start with the piston pump on the left. The brown piece moves up or down in a tube, and the two black "T" figures are valves that open or close in response to water pressure. The down arrow next to the piston indicates that the piston is currently moving down and pushing on the water. This causes the valve at the bottom to close and the valve on the left to open. So water comes out at the top left. After the piston is pushed down as far as it will go, you start pulling the piston back up. This is not shown in the diagram, but now everything is reversed. The valve at the left closes, and the valve at the bottom opens, both in response to the pressure change. So now, water is pulled up from the well or other source, filling the chamber. When it is full, you start pushing down again, and the cycle begins anew: the valve on the left opens and the valve on the bottom closes, pushing water out of the spout at the top left. Once that makes sense, take a look at the plunger pump on the right side of the diagram. You will see that it works on exactly the same principle: when you move the brown part up or down, it pulls or pushes on the water in the same way as the piston pump. The only difference is in the shape of the moving part.
- simongr3dal 8y ago
  The most recent AvE video had a break down of a pressure washer which includes an explanation of a piston pump. https://youtu.be/4IbjQyR9X6E https://youtu.be/4IbjQyR9X6E
- lucb1e 8y ago
  > Your confusion is understandable, since the Wikipedia article doesn't even make the slightest attempt to explain the diagram. A little meta, but in these situations I usually try to improve the source and post a reply saying I edited it, instead of explaining it to one (or a few) person(s) here. Not saying it was bad that you just wrote a big comment explaining it completely! Just an idea of equal effort while reaching more people :)
  - Stratoscope 8y ago
    That's very good advice, thanks for the reminder. I do edit Wikipedia fairly often, but didn't feel like I had enough time to do a creditable job on this topic this weekend. So consider my HN comment a rough draft of an upcoming Wikipedia edit.
- alanbernstein 8y ago
  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.