Closed loop questions

[das75]

Considering a closed loop for my 75G. Since tank is not drilled (nor planning), intake would be a u-tube going over the back wall to a pump below in the stand, or possibly in the basement. For the return, planning a closed perimeter loop with 4 -6 outlets at or just below the surface.

Questions:
-when using the pump head loss calculator, since closed loop assume leave vertical length at zero, wonder though how I bring in pipe length to see the difference in having the pump in the stand compared to the basement
-for the number of elbows etc, do you use just the number on the pump outlet side
-for the u-tube intake and plumbing to the pump, would that be sized to match the input at the pump, any advantage going bigger then reducing just at pump?

 

[Anonymous]

In answer to you first question. I would put in the height, but take it out of the final answer. Elevation adds 1 for 1. So if you pump if 10 ft down and you get 13 ft of losses your flow losses are only 3 ft. Remember you will have flow losses on both sides. So you may have to run it a few times to get everything.

Second question is similar to the first. You need to account for every thing on both sides. You will probably need to run it at least twice. Once of the suction and once for the discharge. IIRC the program is set up for discharge only.

Third question. I always oversize my suction. The larger the pipe the smaller the losses for the same GPH. It is more critical on the suction side if you have to many losses on the suction side you could form vapor pocket at the impeller eye (cavatation) this would damage the impeller and shorten the life of the pump.

 

[Mihai]

Let's start by saying that I don't know the answer to the first two questions. For the third one I agree with Wazzel, go bigger (one size bigger) than the input.

Now back to the first two -> despite the fact that I don't know the answer I'd say not to count either the height or the elbows of the intake (the part going down) as long as they can handle more than what your pump pushes back: think about it this way: if you remove the pump, the water will come rushing out of your tank anyway, so the pump doesn't have to work to pull the water from the tank, so it's not taking the pump's power.
That is as long as enough water comes such that the pump doesn't run "dry" (it will never actually run dry, but will start spending power to suck the water as well as to push it up). Perhaps it is now clear why we advise you to go with the larger pipe size on the intake: to reduce the power spent from the pump for sucking the water...

Again, I'm a networking guy, so I don't know almost anything about plumbing... take it wih a grain of salt.

M.

 

[ChrisRD]

As Wazzel mentioned, there will be form/friction losses on both the intake and the exhaust sides of the pump, but no gravity head losses.

If the calculator has a horizontal pipe length portion, just plug the total pipe length (for the leg you're computing) in there and enter zero for the vertical. This will account for the friction loss of the pipe without the gravity component.

As Wazz also pointed out, you'll probably have to run the suction and pressure legs separately and then add them if you're going to use different size pipe on each...

 

[Anonymous]

Let's start by saying that I don't know the answer to the first two questions. For the third one I agree with Wazzel, go bigger (one size bigger) than the input.

Now back to the first two -> despite the fact that I don't know the answer I'd say not to count either the height or the elbows of the intake (the part going down) as long as they can handle more than what your pump pushes back: think about it this way: if you remove the pump, the water will come rushing out of your tank anyway, so the pump doesn't have to work to pull the water from the tank, so it's not taking the pump's power.
That is as long as enough water comes such that the pump doesn't run "dry" (it will never actually run dry, but will start spending power to suck the water as well as to push it up). Perhaps it is now clear why we advise you to go with the larger pipe size on the intake: to reduce the power spent from the pump for sucking the water...

Again, I'm a networking guy, so I don't know almost anything about plumbing... take it wih a grain of salt.

M.

SInce I do not know the exact calculator he is using I was using the verticl run to get the friction losses. If it has a place to put in a horizontal distance that would be better. You need to count all piping in a closed loop system. Losses on the suction side can cause problems for the pump if they are great enough. The pumps we use can not suck, they are not designed to. The reason we oversize is to reduce the power used, but not to pull the water. The more losses in the system the more power it takes to run the pump.

 

[das75]

Calculator I was using is http://www.reefs.org/pumps/

One of the pumps I'm considering is a Mag18 (3/4" NPT fittings). Since planning a u-tube on intake wondering correct size to as to not restrict pump but small enough for aesthetics. Seen numbers like 600gph on a 1" bulkhead but realize that's for gravity flow, not suction.

 

[Anonymous]

Put in the total length of your pipe in the horizontal section. Include all of the elbows. Do 2 runs one for the suction and one for the discharge. I had a mag18 set up like you are planning and had to use 1.25 pvc. 1" was just not big enough. Another local guy tried with 1" and ended up with 1.5", he skipped the 1.25. If you are going under the stand use 1.25" for the basement I would use 1.5".

 

[das75]

Wow, looking like some big pipe and holes in the floor. Guess could live with the u-tube as 1.5", same for the vertical runs behind the tank, but for the manifold was thinking smaller.

For the return was hoping for a manifold similiar to one here but would have the front corners on 45°s (six sided tank, flat back hex?):
http://www.wetwebmedia.com/pbh2oret.htm

 

[Anonymous]

I guess I was not clear. You only need the 1.5 or 1.25 on the pump suction side. If you are under the tank 3/4" discharge will be fine. If you are in the basment use 1" for the return. Check your losses and compare to the mag18 curve. It may not be the best choise if you are in the basment. The Iwaki or Blueline pumps may be a better selection.