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 flow rate through 1 1/2 inch bulkhead
Author: Anonymous User

I am setting up a fish tank that will have a drain pipe from the tank to a sump below the tank. The drain pipe in the tank will be 24 inches in height. The water from the tank will flow into that drain pipe. That drain pipe will be attached to a 1 1/2 inch bulkhead in the bottom of the tank. From there the water will flow into another 1 ½ inch pipe that will go down to the sump. All are straight pipes. The water will drain through the drain pipes to the sump by gravity.

My question: How much flow (in gallons per hour) can I expect through the 1 1/2 pipes and bulkhead?

I appreciate your thoughts and suggestions.

Chris

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 Re: flow rate through 1 1/2 inch bulkhead
Author: Anonymous User

You should be able to 82.8 gpm's through an 1 1/2" pipe so take it from there.

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 Re: flow rate through 1 1/2 inch bulkhead
Author: jimmy-o (CA)

If the pipe in the tank is 24" high, how deep is the tank? It can only drain down to the top of that pipe?

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 Re: flow rate through 1 1/2 inch bulkhead
Author: jimmy-o (CA)

At what head pressure?

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 Re: flow rate through 1 1/2 inch bulkhead
Author: Anonymous User

Gravity flow through what an 1 1/2" pipe will hold, flow @15 feet per second with minimum head pressure of about 4-5 feet.

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 Re: flow rate through 1 1/2 inch bulkhead
Author: Anonymous User

Billplum,

Thank you. That comes to 4980 gph, which is much higher than the 675 - 1350 gph rate I have heard before.

Chris

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 Re: flow rate through 1 1/2 inch bulkhead
Author: Anonymous User

Jimmy-o,

Thank you for your reply. My plumbing knowledge is nect to zero (as I am sure it appears). I am not sure what you mean by at what head pressure?. The fish tank is 24 inches deep. The drain pipe is about 20 inches tall. The water from the tank drains into the drain pipe by gravity.

Chris

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 Re: flow rate through 1 1/2 inch bulkhead
Author: Anonymous User

Jimmy-o,
The tank is 24 inches deep and can only drain down to the top of the drain pipe which will be about 20 inches tall. The flow is by gravity. Once the water goes into the sump below the tank it will be pumped back up to the tank by a pump.

Chris

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 Re: flow rate through 1 1/2 inch bulkhead
Author: hj (AZ)

In other words this is an overflow drain when the water gets to 20" deep? If so, then the water you will drain through it will be whatever amount you add as makeup water.

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 Re: flow rate through 1 1/2 inch bulkhead
Author: hj (AZ)

Your head pressure is going to be about zero, so your actual flow will be less that quoted. In addition, since it will be "open to the atmosphere", you are going to aspirate a lot of air with the water which is also going to reduce the amount of flow available. What is the capacity of the pump? That will be the maximum you can flow, and if it pumps faster than the water can flow back, you will have to install a modulator on the discharge pipe.

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 Re: flow rate through 1 1/2 inch bulkhead
Author: Phil H

Let's start toward the beginning. How much water do you want it recirculate? Or, what are you trying to accomplish. Depending on the pump you use, the flow through the pipe will be very little or a lot.
Phil

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 Re: flow rate through 1 1/2 inch bulkhead
Author: Anonymous User

Phil H,

Thank you for being patient. Here is the situation. The fish tank will be 120 gallons of salt water. The size of the tank is 4 ft long X 2 ft in width X 2ft in depth. Below the fishtank is a second tank (the sump) which will be about 29 gallons. (the sump is a tank with water in it that will hold the filters, heaters and the return pump) The flow I want to accomplish from the fishtank to the sump and back to the fishtank is about 2400 gallons per hour.

The fish tank will have two drain pipes inside it. Each pipe will be about 22 inches tall and connect to a bulkhead in the bottom of the fishtank. The water in the fishtank will be about 24 inches deep and will flow into each drain pipe by gravity. The water will flow though the drain pipe, through the bulkhead and then into the sump about one foot below the fish tank. The water will then be pumped back up to the fishtank by a water pump that is sitting in the sump.

I need to know what diameter drain pipes I need to have to get a total flow rate of 2400 gallons per hour. The size of the return pump sitting in the sump will be matched to the gallons per hour flow I can get through the fishtank drain pipes.

I have been told that a 1 inch drain pipe in this set up can drain 300 - 600 gallons per hour. [Further I have been told that at flow rates of 600 gph there will be significant water noise.] If a 1 1/2 inch pipe will drain 2.25 time the amount of the one inch pipe, then a 1 1/2 inch drain pipe should drain 675 - 1350 gallons per hour. Therefore if I have two 1 1/2 inch drain pipes I should be able to get a total of betwenn 1350 - 2700 gallons per hour.

I am not sure if the above flow rates are accurate or not.

I do not feel I can buy the return pump (that is in the sump) till I know the drainage flow rate since the pump flow rate (gallons per hour at whatever head) needs to match the drainage flowrate.

So my question is: what is the flow rate I can expect through the 1 1/2 inch drain pipe that is in the fishtank draining intothe sump?

Chris

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 Re: flow rate through 1 1/2 inch bulkhead
Author: hj (AZ)

You will get a lot less flow through the pipe at the top of the tank than if it were coming off the bottom, partly because of the loss of any head pressure. In addition, being at the "water level" the flow is going to create an eddy current that slows the water down and also aspirates air into the pipe which will take up a lot of space that should be filled with water. I doubt that you will get 60 gpm under those conditions because that would be equivalent to draining an almost full bathtub in a minute, which will never happen without a pump sucking the water. You will never accurately match the incoming water with the pump's discharge in an open system. The pump has to be "oversized" with a float to shut it off when it has pumped the majority of water out and turn it back on when the sump is filled.

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 Re: flow rate through 1 1/2 inch bulkhead
Author: hj (AZ)

One other thing. If you do this, putting a piece of plastic verically across the center of the drain opening will eliminate the eddy effect and allow the pipe to drain more water.

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 Re: flow rate through 1 1/2 inch bulkhead
Author: Phil H

Wow, a three minute turnover rate for an aquarium, I never guessed it would need to be that high. Anyway, I can't be too much help cause there are somethings I don't know, some stuff I can't remember, and some things that are really difficult to calculate. Besides that, the answer I come up with seems too high. Theoretically, with 3 ft of head(2 in the tank and 1 out the bottom) and a straight drop, you might be able to get 60 or 70 GPM not subtracting for inlet and outlet losses. These losses might be real significant (that's something I can't remember). I am assuming that your sump is an open reservoir.

I can not see how the drain pipe could ever be made too big except for appearance or cost. If you are worried that the pipe may be too small, put in a bigger pipe. If for some reason it flows too much you can always restrict the flow. If the pipe needs to be venting you will need a much bigger pipe. If it is a flooded pipe and you have problems with vortexing (water circling the drain) at the top of the pipe, you can put a horizontal plate above the pipe. If a big pipe looks real ugly, you can get clear PVC pipe(it is not optically clear like plexiglass, it's foggy with a blue tint and comes in normal pipe sizes and can be used with other PVC fittings).

You might have better luck talking to someone who has experience with fishtanks with the same pumping and filter set-up. I am guessing that you already figured this out, but make sure your sump is big enough to handle all of the water that may drain when the pump is shut-off. You might also want make it so that there is enough reserve in the fish tank above the drain pipe so that it can hold all of the water in the sump, filters, etcetera; this is incase something obstructs the drain pipe and tank can not overflow.

I don't know if this was any help. Sorry for not getting back sooner.
Phil

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 Re: flow rate through 1 1/2 inch bulkhead
Author: Anonymous User

Phil H,

Thank you very much for your thoughts and suggestions. I appreciate your time and efforts. I will use your ideas as I set up the tank.

Chris

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