Overflow gph rule?
- Thread starter coop21
- Start date
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kodi
Guest
If the overflow is rated at 300 gph then your return pump needs to be less than 300 gph. Keep in mind that most pumps loose gph due to head pressure (height from sump back up to the tank). As an example the Mag 7 drops from 700 gph at zero head to about 450 gph at 5 feet of head (a typical height from sump to tank).
IMO the 300 gph overflow is going to be undersized for an 80 gallon tank. I am running an 800 gph overflow with a Mag 9.5 on my 75 gal. The two work well together.
Running an undersized pump allows the overflow to keep up with the volume - if not - your floors are going to get wet, sump will run dry, and pump could burn up.
IMO the 300 gph overflow is going to be undersized for an 80 gallon tank. I am running an 800 gph overflow with a Mag 9.5 on my 75 gal. The two work well together.
Running an undersized pump allows the overflow to keep up with the volume - if not - your floors are going to get wet, sump will run dry, and pump could burn up.
mithrax
Member
Hi, I was told that the return pump must be at least the same gph as your overflow box (if not more.) This makes sense to me since you lose some of the energy driving the water against gravity. The stronger the return pump, the more force you will have in your return water which aids in water circulation. IMO.
broomer5
Active Member
I'm with Kodi on this one.
For an 80 gallon tank I would think an overflow rated between 600 gph and 800 gph would be better.
The explaination on head pressure is right on. All pumps lose true flow rate when having to pump against head pressure. Check the spec's on any decent pump and you will see the various flowrates at various heads. For an existing tank, measure the distance from where you intend to locate the return to the location you plan to place the pump. This distance is the head ( normally in feet ).
Measure this distance in height only to obtain the head pressure, but keep in mind that any elbows, 90 degree turns or reductions in tubing diameters will also reduce the flow somewhat.
It's not so much gravity we are pumping against, but head pressure due to atmoshperic pressure ( 14.7 psig at sea level )exerted on the column of water in the return line. Too much info ... sorry
My swag is an overflow rated between 600 to 800 would be excellent for an 80 gal tank, with a return pump selected for the actually head loss that does not exceed the overflow .... whew
Hope this helps Coop21
For an 80 gallon tank I would think an overflow rated between 600 gph and 800 gph would be better.
The explaination on head pressure is right on. All pumps lose true flow rate when having to pump against head pressure. Check the spec's on any decent pump and you will see the various flowrates at various heads. For an existing tank, measure the distance from where you intend to locate the return to the location you plan to place the pump. This distance is the head ( normally in feet ).
Measure this distance in height only to obtain the head pressure, but keep in mind that any elbows, 90 degree turns or reductions in tubing diameters will also reduce the flow somewhat.
It's not so much gravity we are pumping against, but head pressure due to atmoshperic pressure ( 14.7 psig at sea level )exerted on the column of water in the return line. Too much info ... sorry
My swag is an overflow rated between 600 to 800 would be excellent for an 80 gal tank, with a return pump selected for the actually head loss that does not exceed the overflow .... whew
Hope this helps Coop21
K
kodi
Guest
Mithrax what you have heard is partially correct regarding matching gph. But, the statement needs further explination regarding head pressure. For example, an overflow box rated at 800 gph will work fine with a pump (in the sump) that is rated 800 gph. This is because the true flow rate after factoring in the head pressure will be somewhere around 600 gph, depending on the pump make and model. Again, the important thing is not to exceed a total pump discharge flow rate greater than the overflow.
COOP21 - I am running the CPR 800 gph continuous siphon overflow box with a Mag 9.5 at 4.5' of head. I can run the pump flow wide open and the box keeps up just fine. My only complaint about the CPR box is it has a tendency to create fine bubbles that end up recirculating throughout the tank.
I have made some adjustments that have helped. Feel free to e-mail me if you want more details (mediatrng@kscable.com).
Hope this helps you in your decision.
COOP21 - I am running the CPR 800 gph continuous siphon overflow box with a Mag 9.5 at 4.5' of head. I can run the pump flow wide open and the box keeps up just fine. My only complaint about the CPR box is it has a tendency to create fine bubbles that end up recirculating throughout the tank.
I have made some adjustments that have helped. Feel free to e-mail me if you want more details (mediatrng@kscable.com).
Hope this helps you in your decision.
fender
Active Member
I ain't no expert is physics but...
the reason your overflow needs to be a higher gph than the return pump (even taking into consideration of gravity and head pressure etc.) is wet floors.
An overflow no matter what the flow rate is will only let the water flow until it drops below the slots. MAke your sump capacity capable of handling this so you don't have wet floors should your pump stop. The pump should be evenly matched to keep the overflow from outpacing it and your overflow to empty and lose siphon. The pump and overflow will balance out because your overflow has a limit to what it can actually drain. The pump on the other hand only has a limit on the amount of water in your sump. If it is higher than the capacity of your Overflow, your sump will empty into your tank. If your tank can't handle the extra water.....wet floors. Pump @head should NEVER exceed the overflow.
IMO.
the reason your overflow needs to be a higher gph than the return pump (even taking into consideration of gravity and head pressure etc.) is wet floors.
An overflow no matter what the flow rate is will only let the water flow until it drops below the slots. MAke your sump capacity capable of handling this so you don't have wet floors should your pump stop. The pump should be evenly matched to keep the overflow from outpacing it and your overflow to empty and lose siphon. The pump and overflow will balance out because your overflow has a limit to what it can actually drain. The pump on the other hand only has a limit on the amount of water in your sump. If it is higher than the capacity of your Overflow, your sump will empty into your tank. If your tank can't handle the extra water.....wet floors. Pump @head should NEVER exceed the overflow.
IMO.
broomer5
Active Member
ummmm,
maybe we need to make sure we are talking about the same thing.
I am describing and external hang on the side of tank overflow with U-Tube siphon.
The overflow can never out pace the pump,
the pump can certainly deliver more water than the overflow is capable of handling.
A good designed overflow should never lose it's siphon unless you lift the U-Tube and break siphon.
If the pumps capacity at flowing conditions is higher than the capacity of the overflow - you're correct fender - you will empty your sump and most likely over flow your tank rim.
maybe we need to make sure we are talking about the same thing.
I am describing and external hang on the side of tank overflow with U-Tube siphon.
The overflow can never out pace the pump,
the pump can certainly deliver more water than the overflow is capable of handling.
A good designed overflow should never lose it's siphon unless you lift the U-Tube and break siphon.
If the pumps capacity at flowing conditions is higher than the capacity of the overflow - you're correct fender - you will empty your sump and most likely over flow your tank rim.
tanker newbie
Member
the returning pump should always be more than the over flow! if you have 800 gph comeing down and 799 gph going up, thats 1 extra gallon thats going down every hour, give it time and it WILL over flow!!!
personally i would get something that WITH HEAD will do 900 gph and then controll it with a valve if you have to little water in the sump its better than haveing too much over flowing the tank
i know what its like to have water flood(under the aquarium THE GREAT FLOOD) explanes my story
personally i would get something that WITH HEAD will do 900 gph and then controll it with a valve if you have to little water in the sump its better than haveing too much over flowing the tank
i know what its like to have water flood(under the aquarium THE GREAT FLOOD) explanes my story
fender
Active Member
I think me and broomer are on the same page here. I was trying to be a little simplistic above, but I guess I missed the mark.
Scenario:
Lets assume there is no pump at all.
Overflow has a rate of 1gph.
Your sump has a capacity of 5 gallons and has 3 gallons of water in it.
Assume your tank has 1g of water for every inch of height.
top of tank is 20"
If you have a tank that has a water line at 18".
The bottom of the slots in the overflow is at 17".
after 1 hour
tank level 17" -1gph
sump 4 gallons
after 2 hours
tank level 17"
sump 4 gallons
What happens?????
Nothing.
The overflow stops working.
Period.
No wet floors.
Lets add a pump
pump has a rate of 2gph.
in the same setup
same starting point.
after 1 hour
tank 19" -1gph for overflow +2 for pump.
sump 2 gallons
after 2 hours
tank 20" -1gph for overflow +2 pump
sump 1 gallon
after 3 hours
tank 20" -1gph for overflow +2 pump
sump empty
1 gallon on floor
after 4hours
tank 20" -1gph for overflow +2 pump
sump empty
1 gallon on floor
BURNT pump
Not meant to be a flame.
Just trying to find an answer.
Please show me if I am wrong.
Scenario:
Lets assume there is no pump at all.
Overflow has a rate of 1gph.
Your sump has a capacity of 5 gallons and has 3 gallons of water in it.
Assume your tank has 1g of water for every inch of height.
top of tank is 20"
If you have a tank that has a water line at 18".
The bottom of the slots in the overflow is at 17".
after 1 hour
tank level 17" -1gph
sump 4 gallons
after 2 hours
tank level 17"
sump 4 gallons
What happens?????
Nothing.
The overflow stops working.
Period.
No wet floors.
Lets add a pump
pump has a rate of 2gph.
in the same setup
same starting point.
after 1 hour
tank 19" -1gph for overflow +2 for pump.
sump 2 gallons
after 2 hours
tank 20" -1gph for overflow +2 pump
sump 1 gallon
after 3 hours
tank 20" -1gph for overflow +2 pump
sump empty
1 gallon on floor
after 4hours
tank 20" -1gph for overflow +2 pump
sump empty
1 gallon on floor
BURNT pump
Not meant to be a flame.
Just trying to find an answer.
Please show me if I am wrong.
jbirdy
Member
hello. Does the CPR continuous siphon overflow hold it's siphon during power outages? I am using a U-tube siphon now and this holds the siphon unless I lift the tube. The problem is this thing is too loud. The CPR claims to be quiet. Anyone have this one? Is it really quiet?
Thanks..
Thanks..
broomer5
Active Member
Exactly fender.
Your example clearly shows that if you have a pump that has twice the flow capacity of the overflow - you will certainly overflow the tank, empty the sump and burn up the pump.
In our real world set-ups, the volumes of water are so much greater, we're talking 800 gph in the above posts, that our small sumps would over flow much sooner.
Simple as I can say it is this.
Once the water level in the tank reaches the slots and begins to flow - for every gallon in - there is a gallon out, and your sump level will remain there until evaporation lowers it.
This was a good one
Your example clearly shows that if you have a pump that has twice the flow capacity of the overflow - you will certainly overflow the tank, empty the sump and burn up the pump.
In our real world set-ups, the volumes of water are so much greater, we're talking 800 gph in the above posts, that our small sumps would over flow much sooner.
Simple as I can say it is this.
Once the water level in the tank reaches the slots and begins to flow - for every gallon in - there is a gallon out, and your sump level will remain there until evaporation lowers it.
This was a good one
fender
Active Member
They keep their siphon.
It has an inlet that you are supposed to hook to a powerhead's air intake that will pull the air out. The are supposed to keep a siphon even in a Power outage. This device will reset it by vaccuuming out the air if it is lost.
CPR claims air can accumulate in any overflow and cause it to lose siphon which is why they have the air outlet device in addition to the PO proplem.
It has an inlet that you are supposed to hook to a powerhead's air intake that will pull the air out. The are supposed to keep a siphon even in a Power outage. This device will reset it by vaccuuming out the air if it is lost.
CPR claims air can accumulate in any overflow and cause it to lose siphon which is why they have the air outlet device in addition to the PO proplem.