Hydraulic ram (wikipedia)(youtube) uses the water hammer (wikipedia) to pump water.
Please help me understand how it works.
I understand that the check valve catches the pressure from the water hammer (since when the pressure below the valve is higher then above it, it opens)
What i do not understand is why does the waste valve open (and close)? (and how does it sync with the check valve?)
I guess it has to do with the air chamber (I do not exactly understand what is it for), but I do not understand why does it open?
Images are from here
Best Answer
I doubt if the person who made that animated gif knew how the pump works. It's not at all clear why the valves open and close, and the regular movement of the water is nothing like an actual ram pump. It's more likely to confuse than enlighten people imo.
The waste valve can be a spring-operated normally-open valve that closes when the flow velocity generates sufficient drag. The water in the drive pipe, which is long and rigid (steel pipes will generate higher pressure than pvc), has gathered significant momentum (p=m*v) by that time. When the valve closes, that momentum generates pressure, slamming open the check valve and compressing the air in the reservoir. The check valve closes again, the compressed air expands, pushing water up the delivery pipe. The waste valve reopens and the process repeats.
The air reservoir stores the energy, absorbs the pressure pulses, and provides continuous flow at the delivery pipe. It's comparable to a smoothing capacitor: can handle any incoming current, absorbs voltage (pressure) peaks, and delivers the energy during the whole cycle. Without the air, every time the waste valve closes, the two water columns are in direct contact, one at full speed, the other at rest. That will cause either large pressure peaks (when they meet head on), or large movement of the pump. At 30,000 times a day, they may not last very long.
But the fundamental difference between a pump with air reservoir and one without is the efficiency: without reservoir, energy is transferred by a perfectly inelastic collision: the water in the drive pipe and the water in the delivery pipe have the same velocity after the collision. Not only is that the collision where most energy is lost, the mass in the drive pipe is also the largest mass, and will keep most of its energy after the collision.
With a reservoir, most of the energy of the drive mass is transferred to the reservoir, and all that energy is used to pump the water in the delivery pipe.