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I have just bought a double effect hand pump (a BETO CLD-024NAG) without knowing what to expect. I was very surprised to discover that the pump inflates the tire both when I push and when I pull. How does it work?

Also, the barrel of the pump is at the rear instead of the front (by front I mean where the valves and the manometer are) - is this related to the double effect?

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Pumps have an air chamber (normally cylindrical) that is compressed in order to force the air into the tyre. When the handle is pulled out, air behind the piston is forced out of the cylinder. In single action pumps, this air is vented into the atmosphere and lost (no big deal; there's plenty of it around!). On a double (or dual) action pump, this air is collected and forced through the valve into the tyre.

Single action pumps are mechanically simpler, and so smaller and lighter than equivalent double action pumps, but take roughly twice as many strokes to get to the same pressure. With a double action pump, you have to do work when pulling the pump handle, as well as when pushing, which is more effort per stroke (due to the pressure of the air already in the tyre, unlike in the single action pump, where you're working against atmospheric pressure which is much lower).

  • Can you clarify more effort per stroke? Because I think it's the same effort, and no wasted effort expelling unused air. – andy256 Sep 30 '16 at 8:28
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    @andy256 With a single-action pump, pulling the handle out requires almost no effort because you're just moving the handle and not pressurizing any air. With a double-action pump, pulling the handle out is as hard as pushing it in, because you're pressurizing air and forcing it into the tyre. The "wasted effort expelling unused air" is practically zero: it's the same effort you make pumping the pump when it's not connected to your tire, for example. – David Richerby Sep 30 '16 at 8:37
  • @andy256, I've added a bit to explain my thinking - maybe I'm wrong, in which case I'll delete that bit of the answer. I think that each stroke (in and out) is more effort than the single action version, but overall less effort is wasted. – srank Sep 30 '16 at 8:38
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    Note the "pull" stroke is not as efficient as the "push" stroke due to the longer high-pressure connection up the side of the pump. I couldn't find a good cutaway diagramme of a 2 way pump, will draw one if requested. – Criggie Sep 30 '16 at 9:17
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    Note that the reason for having a double-action pump is not to reduce effort, but to get the job done faster. Pumping up a tire with a shortie pump is a half-day affair. The double action allows you to accomplish the task in only 2-3 hours. – Daniel R Hicks Sep 30 '16 at 12:20

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