Sorry if this doesn't quite fit the area, but I feel it it does. I was playing around with a pump just now seeing if the actual flow rate matches the manufacturers head loss chart and I had a thought. When calculating head loss I'm holding up the tube at the point of where the top of the tank is. However in reality, if the return tube is submerged (even with a seal break) should I only be calculating the head loss from the pump to the BOTTOM of the tank considering that the water in theory would supply back pressure to that point thus not actually using much effort to "lift" the water but only "move" the water from the bottom to the top of the tank. Hopefully I'm explaining this right.
Head loss, have I been doing it wrong all along?
- Thread starter savannah_az
- Start date
If both the suction and discharge are submerged in the tank and the suction line feeds directly into the pump this is basically a closed system. The head height of both lines are the same if you consider a typical canister filter. With the head height being the same for both they basically cancel each other out leaving friction loss which is usually going to be really low.
The vertical height comes into play when the pump is installed in a sump type install or where the suction line to the pump is fed from a source lower than the total height of the discharge.
The vertical height comes into play when the pump is installed in a sump type install or where the suction line to the pump is fed from a source lower than the total height of the discharge.
This is a sump setup, so obvious there will be head loss from the pump to what I always thought to be the top of the tank, but considering that the return will be submerged does that mean from the bottom of the tank to the top I'm essentially just pushing, not lifting?
If I'm understanding you, no. If you're pumping from a sump the highest point of your return to the tank is your static head in inches or feet. Having the return submerged doesn't change change anything there. The supply to the sump isn't adding any additional pressure to the inlet of the pump.
The total head is the sum of the static head and the friction head. If both the pump intake and return are submerged, the static head is the difference between the sump level and the tank level. The friction head is harder to estimate which is the frictional head loss through the pump conveyance hoses calculated from hydraulic chart. For a canister system, there is no static head, only friction head, as both intake and return are submerged in the same tank level. If the return is situated above the tank level, the static head is increased slightly by the clearance between the return hose and the tank level.
Right, I understand that a canister is essentially a closed loop, but my thought process was that if the return is submerged, obviously there is enough pressure to equalize the water level. So working with that theory, should the "static" difference only be between the pump point and the bottom of the tank because at that point it becomes a matter of friction loss only?
No, the fact that you have additional tubing going down into the display tank won't reduce your static head, however it will actually increase your friction head because the water has to flow through a longer run of tubing (although the additional friction head is probably miniscule at the length we are talking about here).
Static head is the distance from the water level in your sump to the level the water is being pumped vertically (assuming your pump is placed at or below water level).
Are you asking because you are getting more GPH than advertised? I was actually planning to do my own test this spring to see what the real shutoff head is for my Laguna 4200 pump. Curious to see if you are running a similar test and if so, what your results are.
Static head is the distance from the water level in your sump to the level the water is being pumped vertically (assuming your pump is placed at or below water level).
Are you asking because you are getting more GPH than advertised? I was actually planning to do my own test this spring to see what the real shutoff head is for my Laguna 4200 pump. Curious to see if you are running a similar test and if so, what your results are.
This all came to a point when I was drilling holes in a wet dry drip plate, I started doing the math to figure out what flow rate I was going to get. I'm running a waveline6000 and it seems like I'm currently pushing more than the manufacturers graph (surprise!) so I was just thinking about back pressure from the tube and thinking if that would come into play at all.
Here is a diagram that illustrates how to obtain the static head. There is no easy way to estimate the friction head as it depends on how long the hose is, how many and how sharp the turns are, and how much resistance the flow path encounters.
Right, I guess my original thought was considering if static was the top of the suction force (sine the water level tried to equalize) to the BOTTOM of the discharge tank (again because the water level would have the same pressure, same idea as it trying to equalize in a sense). Apparently I was way off but hey you never know if you don't ask right!