Foot pump?

[angrybear]

Maybe the Lada Car company were right in their decision to issue a stirrup pump then.

But you can alternate the use of your left and right leg when operating a foot pump. I always do.

I haven't seen a killer reason yet for a foot airgun pump not being feasible.

Well let me explain my post #6

A foot pump has a wide bore with a short stroke, perfect for low pressure, it probably has a surface area of 2+ square inches so is easy to pump a tyre to 30psi because that' s only 60lbs of force & your legs carry more than that around all day.

The high pressure stirrup pump has a long stroke, to get reasonable volume, but very narrow diameter, to reduce the surface area because 200bar is around 3000psi so if the piston was 1 square inch it would take 3000lbs to push it down, in a stirrup pump the high pressure piston is probably under 1/4" dia so a surface area of 1/20th square inch, which "only" takes 150lbs to pump.

You cannot have the short stroke of a foot pump move enough volume with the required small surface area to develop the pressure.

[Antoni]

Well let me explain my post #6

A foot pump has a wide bore with a short stroke, perfect for low pressure, it probably has a surface area of 2+ square inches so is easy to pump a tyre to 30psi because that' s only 60lbs of force & your legs carry more than that around all day.

The high pressure stirrup pump has a long stroke, to get reasonable volume, but very narrow diameter, to reduce the surface area because 200bar is around 3000psi so if the piston was 1 square inch it would take 3000lbs to push it down, in a stirrup pump the high pressure piston is probably under 1/4" dia so a surface area of 1/20th square inch, which "only" takes 150lbs to pump.

You cannot have the short stroke of a foot pump move enough volume with the required small surface area to develop the pressure.

That is a somewhat blinkered view.

It's not about the dimensions of the piston(s) or cylinder(s) which will of course need to be as necessary, it's about how to best use the power of the human engine to achieve the desired result. It's about how that power can be best harvested.

This is all about the conversion of the chemical energy contained in the combination of Weetabix, milk and strawbery jam, to the potential energy contained in an airgun's high pressure air tank.

A tool should be designed so that the conversion should be done with as little of the energy contained in the Weetabix dissipated in the form of human body heat (and therefore sweat and fatigue) and the maximum energy transfered to the tank.

Basically, I'm asking whether a better mousetrap could be built along these lines. After all, it's well-known that if you can design and build a better mousetrap the whole world comes knocking on your door to buy it.

[derekm]

It would probably be possible to design a foot pump with a low pressure section feeding the higher pressure section(s), but the stroke would be so short that it would take a very long time to produce a useful volume of HP air. Possible, yes; practical, no.

[Antoni]

Why would the stroke have to be short?

Take the design of the car foot-pump with its short stroke away. We are simply talking about a foot operated pump. Any design you could think of.

The stroke could be any length the mechanical design sets it to be.

[Phil Russell]

That is a somewhat blinkered view.

.

No, I am afraid it is not a blinkered view; it is scientific fact. In order for a foot pump to be produced it would need to follow the basic laws of physics and follow the design of the multi-stage stirrup pumps. So, yes, I guess you could design a foot operated pump that incorporated the numerous stages to generate sufficient compression pressure but I strongly suspect it would be more difficult to operate than the stirrup pump. Look at the current stirrup pumps and consider the length of the compression stroke. At its simplest a foot pump would not have that length of pump due to the anatomy of the knee/hip joints. So an even more complex multi-stage mechanism would be needed. Maybe it could be done but given the effort required to operate today's stirrup pumps I think you would find it very difficult to use unless you were lying on your back as in a 'bench press' machine (is that the right term?).
Have a go ... get a stirrup pump, bolt it to the floor, add a foot plate to the handle and try pumping it with your foot.
Phil

[Antoni]

...So an even more complex multi-stage mechanism would be needed....

Yep, it would.

[angrybear]

That is a somewhat blinkered view.

It's not about the dimensions of the piston(s) or cylinder(s) which will of course need to be as necessary, it's about how to best use the power of the human engine to achieve the desired result. It's about how that power can be best harvested.

This is all about the conversion of the chemical energy contained in the combination of Weetabix, milk and strawbery jam, to the potential energy contained in an airgun's high pressure air tank.

A tool should be designed so that the conversion should be done with as little of the energy contained in the Weetabix dissipated in the form of human body heat (and therefore sweat and fatigue) and the maximum energy transfered to the tank.

Basically, I'm asking whether a better mousetrap could be built along these lines. After all, it's well-known that if you can design and build a better mousetrap the whole world comes knocking on your door to buy it.

It has been, you plug it in to the mains & flick the switch, absolutely minimal effort

With the stirrup pump you could place a seat on the handle & use your body weight to compress it, while using those leg muscles to raise your posterior for the next stroke
Or you could attach a pivoting lever to the top (like an old water hand pump) to get a better mechanical advantage, but the throw on such a lever would be impractical.

If you use a stirrup pump correctly, once it gets hard to pump you bend at the knee with arms & back straight so your whole body weight can compress the lever.

Speaking as someone who used to ride kickstart only motorcycles, mechanical advantage on a foot "pump" aint all it's cracked up to be

[derekm]

Why would the stroke have to be short?

Take the design of the car foot-pump with its short stroke away. We are simply talking about a foot operated pump. Any design you could think of.

The stroke could be any length the mechanical design sets it to be.

How high can you lift your leg and still apply plenty of weight to it??