Closed Loop Head?

[Ratpack]

OK, I am about to drive myself crazy trying to figure out which pump I want to use for my CLS. But I think one piece of info would help me make that decision. How do you calculate the head for a CLS? For returns I use the physical height, 90's and pipe length to get the head in feet, but what about CLS?

[Ninong]

If you locate your CLS pump on the same level as your tank and very close to your tank, then you have virtually no head at all. Roughly speaking, you have one foot of head for each 10 linear feet excluding any vertical rise. In other words, if you stick your pump on the same level with your tank but 10 feet away, then that would be one foot of head, 20 feet away would equal two feet of head, etc.

Naturally you have to figure in any bends in your plumbing and adjust for those, if any. Most charts show 1-ft, 4-ft, etc. Use the 1-ft numbers for a CLS pump that is right next to the tank without any crazy plumbing involved.

[Ratpack]

Thanks Ninong, that helps me make up my mind. I do have one other question though and hate to start another thread for a simple answer. My overflow will be a 1 1/2" pipe, how much flow will that give me to the sump?

[Ninong]

Thanks Ninong, that helps me make up my mind. I do have one other question though and hate to start another thread for a simple answer. My overflow will be a 1 1/2" pipe, how much flow will that give me to the sump?

It will give you way more than you need for a 90-gal tank. Exactly how much you can push through a 1.5" drain depends on what sort of standpipe you use but you should be able to get about 2,000 gph. Remember that a single 1.5" drain can handle more than two 1" drains.

Your maximum flow may be limited by the amount of flow your weir can handle and by the amount of flow your sump can handle more than what your 1.5" bulkhead drain can handle.

[Ratpack]

OK, I need someone to verify my calculations. I mocked up my CL system and this is what I came up with. It will be 1 1/2" PVC throughout. The pump will be located below the tank in the stand but static head still should be 0 as the water coming down is helping push the water up. The entire CL system will have about 20' of straight PVC, 5 T's, 8 90's and 2 45's. According to charts I have seen on PVC friction loss, this equates to about 80' of straight pipe. I used 60 gpm (3600gph), which is the highest flow rate they had, and the friction loss was listed at 20ft head per 100ft run. So using 80' of pipe with this friction head loss comes to 16' of head. So do I use that when choosing my pump for the CL?

[Ninong]

The entire CL system will have about 20' of straight PVC, 5 T's, 8 90's and 2 45's.

That's a lot of T's and 90's! Obviously you can improve the flow dramatically if you can use Y's instead of T's, etc. Without seeing an exact diagram of what you're planning, I have a hard time estimating anything. To tell you the truth, I never bother to calculate the actual pressure loss (including loss from friction) that a hydraulics engineer would have to do. I simply use the rule-of-thumb estimates that have been published in the aquarium hobby literature for years: 10' of lateral pipe = 1' of vertical pipe, etc. One 90 = 1' loss, one 45 = 1/2' loss, etc. These are just rough estimates, not actual measurements of any kind.

Check out this website for some valuable information if you want to do the actual math. WetWebMedia probably has a lot of helpful hints on plumbing closed loops, too.

[Ratpack]

Those estimates actually come from the calculations of sch 40 PVC. When I used the straight length equivilent, I got the same friction loss as I did just counting the T's, 90's and 45's. Here is a drawing of what I am planning to do. The large back view shows how the return will come from the pump, Tee into two legs and then two more legs Tee of of that. The side view shows how the two low outlets will have a T where one side isa pointing towards the bottom to blow detritus from under the LR and the top has a 45 to push water flow up through the rock. The top outlets will have a 45 on each pointing towards the middle of the front pane where hopefully they will meet and become more random and turbulent.

I will most likely use more 45's than 90's to help with flow when possible, but I want to look at worst case.

All of this just to decide if I order the Sequence Dart or Barracuda for my 75g BB tank.