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Old 04-28-2007, 01:48 PM   #1
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Replumbing my Rena XP2, need help!!

I have a 24 gallon nanocube and I just bought a Rena XP2 to add some extra filtration. The problem is when you close the lid on the nanocube there is no open space to get tubing in unless you go through the feeding lid on the front which looks really ugly. There are however two tiny holes in the back in the center of the hinges where you could possible get tubing. I have checked and found that you really can only get 3/8 inch tubing through comfortably without a problem. Therefore I was thinking I would use a reduction coupling from 5/8 (Rena standard tubing) to 3/8 tubing on the last foot or so. Would this cause a problem with my filter? Will it reduce the life of my filter? I don't mind if the flow rate is slightly reduced because I am overfiltering the tank to begin with. According to incompressible fluid dynamics theory, the pressure drop in pipe goes linearly with the diameter of the pipe. So I should experience about a 67% increase in pressure drop over that last foot of tubing. However I wouldn't imagine the pressure drops in the tubing to be the real limiting factors in filters, I would think it would be the pressure drop through the filter. Anyways whats your opinion?

Also I envision a plumbing system on my pump that is as follows. I would have one three way valve on my outlet of the filter, one position connects the filter to the tank and another connects it to a section of tubing that I have go out my window. Another three way valve in on the intake and goes to my 6 gallon jug where I prepare my backish water in. Lets say I want to do a 3 gallon PWC, all I have to do is switch the first three way to vent the outlet water out the window until I get about 3 gallons. Then turn it back to the tank. Then take the other three way valve and pull water from my 6 gallon reservoir until I fill the tank back up. I would have to be careful to make sure I would have suction on the reservoir but I figure a one way on the end of that tubing and prefilling the tubing with water will prevent any problems. Let me know what you think?

I was thinking of getting the reduction coupling, PVC tubing and possibly three way valves (they don't seem to have the correct size three ways) at www.Mcmaster.com. They are in NJ so I get their shipments in a day or two. I was thinking of using the tubing barb fittings. Do you really need clamps on the barb fittings?
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Old 04-30-2007, 05:31 PM   #2
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Preliminary experimentation show that there is quite a decrease in flow rate even through a 6 inch section of 3/8 tubing added to the 5/8 Rena tubing. I don't know if this is totally the 3/8 tubing's fault or the restirctions in the reduction coupling.
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Old 04-30-2007, 06:14 PM   #3
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How about having multipul outputs? Like a 3 way output...If that makes sense.
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Old 05-01-2007, 03:34 PM   #4
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Yeah, I see what your saying but it turns out there are only two holes in the hood, enough for one inlet and one outlet.
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Old 05-01-2007, 03:49 PM   #5
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I take it you don;t want to make any more holes?
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Old 05-01-2007, 04:58 PM   #6
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Your flow will drop as a square of the change in diameter of your tubing.

Drill holes (IMHO).
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Old 05-02-2007, 03:31 AM   #7
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I used to do a lot of fluid dynamics research back in undergraduate so I "should" be able to actually calculate this.
http://www.engineersedge.com/fluid_f...ssure_drop.htm

For a given pressure drop dP in the system (determined by your filter motor) and for constant length of tubing and properties of water, the friction factor times the velocity squared divided by D is constant. But for laminar flow the friction factor equals 64 divided by the Reynolds number, but the Reynolds number is proportional to the velocity and the diamater. This leads to the fact that the velocity squared divided by the diamter squared is constant. Therefore for laminar flow the velocity increases linearly with decreasing diameter. And as I remember if you start becoming turbelent that exponent starts increasing from 1 up towards 2. So the real exponent is some where in between.

Enough useluss math, I went ahead and actually tried it and was not pleased. The flow rate seemed to drop down to about half. This is unnaceptable so I am going to have to figure something else out. I am toying with the idea of drilling holes but I think that is my only option.

Thanks your help guys, be sure to stay tuned to my other plumbing experiments
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Old 05-02-2007, 10:13 AM   #8
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Quote:
Originally Posted by helicopter
Thanks your help guys, be sure to stay tuned to my other plumbing experiments
I've been watching them.
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