Help with "maximum suction lift"

[Daryl Chin]

Hello, I'm in first year Chemical Engineering. Our final project is to build a treadle pump. It's basically a column with 2 check-valves, an "o" ring and is dependent on reciprocating force to pump the water. Maximum suction lift is an important principle that all the groups are having trouble with. Through research, I have found that it is by definition, the maximum height that water can be lifted. It depends mostly on altitude (atmospheric pressure) and also on suspended particles, density of the fluid, and frictional loss. For sea level, the typical maximum suction lift for water is ~25" or (6-7m).

 

Now, each group was interviewed by our professor and he asked every group what this maximum suction lift range applies to our pumps. Apparently, all the groups got this question wrong and he still won't tell us the answer. Any help would be appreciated. My current idea is that this maximum suction lift range applies to the distance from the first check-valve (at the bottom of the pump, where water enters) to the second check-valve. I'm thinking this because though the pump dips below the water level, water only enters through that first check-valve. As one pulls on the handle of the pump, a vacuum is created within the column and so water rushes in to pressurize it. (to my understanding) So, I'm thinking that if the column was longer (around 10m for example), it could lift water between the two check-valves to a height of only 6-7m. I'm not sure, there hasn't been many useful resources on the net.

 

I hope all of this was understandable; it's kind of hard to explain. Any help would be awesome, thanks.