external pumps and plumbing

[neuroslicer]

For all the plumbers and engineers,
I know that some external pumps can tolerate a reduction of their output flow (via a ball valve for example) while others might not be able to tolerate the increased resistance. What are some pumps that can and cannot have their flow cut back by such a method?

thanks.
Jay

 

[Rendos]

Most can tolerate the output being restricted...but not the input to the pump. You are safe with GenX, Sequence, and Blueline pumps for sure.

 

[neuroslicer]

Thanks R. I would imagine that a pump that is experiencing a 20 foot head (and the resultant reduction of water flow) might be experiencing something similar to reduced water flow via a ball valve. The Blueline Velocity pump I have (T3) is rated for a maximum total head of 28 feet.

 

[schigara]

I have seen a lot of setups where the return is restricted with a ball valve and don't understand why they don't Tee off of the return pipe and put the ball valve inline of the thrid leg and return it back to the sump.

This way pressure is bled off and no added load on the pump.

 

[aharvey]

You also have to take into account the diameter of the pipe used to a degree.
If the return side of the pump has a 3/4" end and you increase that to 1" you have increased the size of the water column that the pump has to push and decreased the height that the pump can push that increased weight. (A 1 foot tall column of water with a diameter of 3/4" weighs less than a 1 foot tall column of water with a diameter of 1")
If your pump is over sized for your application then diverting some of that water back to the sump is a very effective way to minimize the wear on the pump.
Place a T above the pump with a ball valve to control the amount of flow back into the sump.
If you really want to get crazy then on the pipe that is carrying the diverted water back to the sump, add one more T then a ball valve and a hose barb on the end.

Instead of diverting water to the sump you can hook up a hose and drain off water into a waiting bucket.

 

[Siffy]

<a href=showthread.php?s=&postid=11308554#post11308554 target=_blank>Originally posted</a> by schigara
I have seen a lot of setups where the return is restricted with a ball valve and don't understand why they don't Tee off of the return pipe and put the ball valve inline of the thrid leg and return it back to the sump.

This way pressure is bled off and no added load on the pump.

Here's 3. On some pumps throttling them back is actually good for them. It typically lowers the wattage drawn by the pump. And they may not want the added flow within the sump/refugium.

 

[just dave]

<a href=showthread.php?s=&postid=11353507#post11353507 target=_blank>Originally posted</a> by aharvey
You also have to take into account the diameter of the pipe used to a degree.
If the return side of the pump has a 3/4" end and you increase that to 1" you have increased the size of the water column that the pump has to push and decreased the height that the pump can push that increased weight. (A 1 foot tall column of water with a diameter of 3/4" weighs less than a 1 foot tall column of water with a diameter of 1")

I know that seems like that would be the case but it is not so. Not so as in it is harder on the pump as the pipe diameter increases due to the weight of the water in the column.

Take a BL HD100 pump (1900gph@0') that has 1" inlet and outlet. Plumb it so the inlet is unrestricted and the pump is pumping into a straight pipe five feet long with one outlet.

The following will show the above mentioned pumps output with a five foot pipe with various diameters.
3/4"= 1619gph
1"= 1768gph
1.25"=1821gph
1.5"= 1831gph
2"= 1839gph
2.5"= 1841gph
3"= 1842gph

As you can see when the pipe is small it's output is noticeably reduced due to the friction created from the pipe. As the diameter increases the out put increases but it reaches a point of diminishing returns.