How does limitation affect velocity at which water enters the sampling pump
How does limitation affect velocity at which water enters the sampling pump?
Our biggest concern with low flow purging and sampling is what do we mean by low flow and it's not really just the flow rate measured at the wellhead but it's the flow of water through the well stream. What we are trying to achieve of course is to not greatly exceed the ambient groundwater flow. No matter what we do of course by pumping, we accelerate water toward the well screen zone, we can't avoid that. But that established limit of about 10th of a flip per second or 3 cm/second through the screen zone is to try and maintain laminar flow through the screen and into the wellbore. And I would say that in essence a 10th to 3/10th per second are about the limit so if you go back and look at books like Groundwater and Wells, Driscoll’s work and others, for maintaining that laminar flow. So it’s not really an issue of how fast the water is moving in the pump but how fast it's moving through the screens slots. You can quickly calculate that by just determining the open area of your screen say example a 10 foot long screen that had a 20 slot opening might have about 3% open area and if you calculated at a 10th of a foot per second, you end up with flow at around a liter to a liter and quarter per minute max.
Our biggest concern with low flow purging and sampling is what do we mean by low flow and it's not really just the flow rate measured at the wellhead but it's the flow of water through the well stream. What we are trying to achieve of course is to not greatly exceed the ambient groundwater flow. No matter what we do of course by pumping, we accelerate water toward the well screen zone, we can't avoid that. But that established limit of about 10th of a flip per second or 3 cm/second through the screen zone is to try and maintain laminar flow through the screen and into the wellbore. And I would say that in essence a 10th to 3/10th per second are about the limit so if you go back and look at books like Groundwater and Wells, Driscoll’s work and others, for maintaining that laminar flow. So it’s not really an issue of how fast the water is moving in the pump but how fast it's moving through the screens slots. You can quickly calculate that by just determining the open area of your screen say example a 10 foot long screen that had a 20 slot opening might have about 3% open area and if you calculated at a 10th of a foot per second, you end up with flow at around a liter to a liter and quarter per minute max.