Pump head calculation - Tricky Question.

[nasotang00]

This is kind of a strange question but I am going to be upgrading from my 55 gallon to a 125 AGA overflowed tank. I think that it is an AGA? Anyway, if I total all plumbing that will be going from my return pump i come up with a total of 12 feet of tubing with 6 90 degree elbows. The 6 L's would equal 6 feet of additional head loss. The main tubing is: (this is for dual returns with one pump)
1' vertical from pump to T
2.5' horizontal to the right overflow L connection
2.5' horizontal to the left overflow L connection
2' vertical up the right overflow L connection
2' vertical up the left overflow L connection
Both left and right outputs have an additional L (which would make a U to go down the outside of the overflows about 6" to expel the water at midtank from the back.
I would like to purchase a pump to accomplish this and maintain atleast 1000 -1200 gph. My long winded question is that the total height that will be pumped Up to the tank is about 4 feet. But with 12 feet of piping and 6 L equaling a total of about 18 feet.
Am I looking at this correctly? Do I need a pump that will pump 1000 gph at 18' head???
Thanks all, you advice and knowledge is eagerly accepted.
~naso

 

[broomer5]

nasotang00
The best way to determine total pressure drop of any system with valves, fittings and straight runs of pipe is to first figure out the total "equivalent straight length of pipe."
Do this first, prior to calculating the pressure loss to overcome any vertical head pressure from your pump to your tank.
In other words, add up all the "equivalents" that you have determined, and see what you have in friction loss / pressure drop of that total straight run. No vertical head introduced yet. Assume you are pumping in a horizontal run.
Each fitting has a value given to it that represents it's equivalent straight run of pipe value. This value is the length of pipe in feet and is called "L".
The lenght of pipe in feet "L", or the "L/D" in pipe diameters is the equivalent length of straight pipe which will cause the same pressure drop as a fitting under the same flow conditions.
The resistance coefficient "K", varies greatly from different types of pipes and fittings, but for calculating a sump/return pump/overflow, we will keep it as a constant.
After determing the total "straight" pipe equivalent - then you factor in the vertical head pressure value in feet.
The way I see it, you'll have
Pump
1 foot section of vertical up run to the
Tee
Branching off left and right ( each 2.5 feet horizontial run )
(2) 90 elbows horizontal to vertical up
(2) 2 feet sections of pipe vertical up
(2) 90 elbows vertical to horizontial
(2) short pieces of pipe horizontal
(2) 90 elbows horizontal to vertical down
I've got the info here, to figure out the total straight run equivalents - but first
What size pipe are you planning to use ?
PVC ?
Internal diameter of the PVC pipe would be helpful, but I think I can look it up.
see ya

 

[nasotang00]

I have been waiting for YOU broomer. You da man!

As for the size of pipe, I guess that it will all be 3/4" from pump to top 90 deg elbow on the overflows then to 1/2" for the parts of tubing in the tank itself.

 

[broomer5]

I don't think you'll get the flow you want using 3/4 inch pipe from your pump on up.
If you're shooting for 1200 GPH ( 20 GPM ) that will be a little over 12 feet per second velocity through the 3/4" pvc pipe, which can cause additional pressure drop. Plus 12 fps is humm'n along pretty fast for an aquarium application.
You want to go with a larger pipe size ??
Say 1" or 1-1/2"
1" would put you around 7 fps
1-1/2" about 3 fps
What ya think naso ???

 

[squidworth]

Wow, I know who I will ask my tricky math type questions now. But what color was the bus drivers hat?

 

[broomer5]

Okay naso,
Calculated everything using 1" PVC Schedule 40 pipe with internal pipe diameter of 1.029 inches.
Equivalent Straight Feet Pipe for each fitting values are below.
Equivalent Straight Feet Pipe:
(1) 1" Tee = 6 feet ( flow up into tee then branches left and right )
(4) 1" 90 Elbows = 2.25 each x 4 = 9 feet
(2) 3/4" 90 Elbows = 2 x 2 = 4
Straight sections of 1" PVC Schedule 40 pipe:
12 feet = 12 feet
Total all fittings = 19 feet Equivalent Straight Feet Pipe
Add this to your 12 feet of 1" PVC pipe
Total = 31 feet of Equivalent Straight Feet Pipe
31 feet of 1" Schedule 40 PVC pipe will give you about 6.5 feet of head loss
You have 4 feet vertical head
Total head loss all components and vertical head loss = 10.5 feet - this is the number !
1200 GPH is your desired flow
That's 20 GPM
That's about 7.42 feet per second running through the system if you did not have the tee installed. With the tee, obvioulsy the velocities will be reduced afer the flow braches off to the left and right.
But for sizing the pump - it does not make a huge difference - the head is still reduced from all the fittings and pipe sections.
The numbers above are correct to the best of my knowledge.
I got the data for calcs from books I use for work when sizing control valves, Crane Valve and Fitting Engineering Handbook, and +GF+ Signet PVC pipe schedule data.
Look for a pump that will deliver 1200 GPH at a vertical head of around 10 feet and you will be golden !
Later

 

[nasotang00]

All hail the broomer !!!
Now, can you put that in plain english or at least,,,,,talk to me like i am 3 years old. Just kidding.
That gives me a great guide line for the system. You are probably right about the turn over rate that I am looking for. I thought that 10 times was what you should do as a rule of thumb. Is that not true for the sump application? Is it not true that reducing the piping down the line create more water pressure? the tubing for the returns in the overflow unit will have to be 3/4 inch. So if I were to look to get something lower, say like 850 - 1000 gph i can still look for a pump that will produce that range at 10.5 head?
Now if the pump has a 1' outlet and I changed the Tee and the tubing FROM the Tee to 3/4" the rest of the way, can I still get at least 850 gph.
Your help has been and always will be appreciated. Thanks buddy!

 

[broomer5]

nasotang00
Most everything I've read recommends between 5-10 turns per hours. That does not mean it HAS to be 5-10 turns through the sump though.
There are rules of thumb for passing water over filter media, and similar "rules" for turns per hour total circulation. Sort of the same but for different reasons.
Reducing the pipe diameter downstream from the pump does not create more pressure - it actually causes a pressure drop by increasing the water's velocity. They go hand in hand. Flow is a function of pressure drop - you MUST have a pressure drop for flow to even occur.
From the pump to the open tank ( to atmospheric pressure ) - is your pressure drop - thus you have flow.
If the pump pressure remains constant, going from a larger pipe diameter to a smaller pipe diameter downstream will only increase the velocity - not increase the pressure. Reducing it too much can cause an increase in your static pressure - but the pressure will never be more than the pump is capable of producing against a dead head shut off.
Think of it like pinching off a garden hose when you're out washing your car in the driveway. It looks like you have increased the pressure - but you haven't, only decreased the opening of the hose, introducing a "restriction" in the end of the hose, causing a huge pressure drop at the end orifice of the hose, and thus increases the velocity of the water. The water coming out hits your car harder, but your house's water pressure at the spigot did not increase. Do a search on "Vena contracta" if you want to see more about it.
850 GPH ( 14.17 GPM ) in a 3/4" PVC pipe will have about a 9 feet per second velocity. That's pretty fast. Think about it.
Here's what I would do to allow you the best of both worlds.
Off of you pump, come off that with a length of pipe to a tee. Let the water flow through the straight part of the tee. Off of the "brached" end of the tee, install a pvc ball valve and pipe it back to your sump. Shut the ball valve off and you will have full flow from your pump to your tank. Opening the ball valve will act like a single valve bypass, allowing "some" of the water to flow back to your sump. This will cause some extra water movement in your sump, so if you do this, be aware. This will also help to protect your pump. Many folks will install a ball valve inline with the return line back to their tank. This is fine, until you shut it off TOO much, allowing the pump to deadhead against the ball valve. Can lead to premature pump failures or blow out seals.
You'll get your flow using 3/4 inch piping - it will just be moving at a quicker velocity.
HTH and I wish you much luck