Plumbing question

oilfieldsafety · #1 03-17-2009, 06:08 PM

So I was plumbing up my new (used) 90 and a question came to mind, this is my first system that will have a sump so I was more or less going to match what I have seen done on other systems that I have seen. Most of these have been plumbed with 1" line running from the pump to the tank even though the output of the pump was 1/2 or 3/4 inch. Now I assume that this was done with friction in mind and wanting to get max flow, but by going to a larger diameter pipe won't you increase your head pressure due to weight of the water column and in fact decrease your flow? Thoughts?

Shane

fkshiu · #2 03-17-2009, 07:12 PM

You, sir, are correct!

http://www.reefcentral.com/calc/hlc2.php

sphelps · #3 03-17-2009, 08:36 PM

No sir, you are not correct

Actually head pressure is equal to density x gravity x height. The diameter of the pipe doesn't actually effect head pressure, only the height difference between the two water levels. However pipe friction also adds to head loss and the larger the pipe the less friction. In other words 1" pipe will flow the same as 6" pipe in theory but with pipe friction the 6" pipe will actually allow more flow than the 1" pipe. The bigger the pipe the better!

Myka · #4 03-17-2009, 08:40 PM

I'm with fkshiun on this one! If you pump 500 gph through a 1" pipe you will get a lot more psi coming out the end than you will if that pipe was 4". That's not difficult to wrap the brain around. However, it is much more difficult on your pump to pump the water through a 1" pipe than though a 4" pipe because it will have to work harder because of the resistance.

banditpowdercoat · #5 03-17-2009, 09:19 PM

In theory, running a larger pipe will NOT increase head pressure because its measures in a 1" square area for PSI. BUT, the pump outlet is a specific diameter. Lets use 1" for this example. Now, take the 1" pump outlet and increase the pipe size to 4" for the rise up to the tank. Now the pump will only pump so much, Right? Should not pump any more GPH with a 1" pipe or a 4" when pipes are run horizontal. BUT. The weight of the water in the 4" pipe is much heavier than the 1" for each foot of pipe for the vertical rise. Now, the pump outlet is still 1" diam, even though the 4" pipe. This creates more head pressure at the PUMP because the pump has all the weight of the 4" pipe's water forcing into a 1" pipe. It's Hydraulics principle. The reason Hyd cylinders can have so much force with a little power input.

Reefer Rob · #6 03-17-2009, 10:08 PM

Hmm, sounds like what you guys are saying is eventually you could have a large enough diameter pipe that the pump wouldn't be able to lift the water.

If you went say 5ft down in a pipe that was... say the size of a swimming pool it would still be the same psi as 5ft down a 1" pipe, just a smaller area so it wouldn't feel like it. Therefore it wouldn't exert any more force on a 3/4" outlet of a pump.

It's all about PSI. 10 PSI on a 4" piston with exert twice as much force as 2" one, but the pump won't have to work any harder.

sphelps · #7 03-17-2009, 10:09 PM

Quote:

Originally Posted by Myka

I'm with fkshiun on this one! If you pump 500 gph through a 1" pipe you will get a lot more psi coming out the end than you will if that pipe was 4". That's not difficult to wrap the brain around. However, it is much more difficult on your pump to pump the water through a 1" pipe than though a 4" pipe because it will have to work harder because of the resistance.

Quote:

Originally Posted by banditpowdercoat

In theory, running a larger pipe will NOT increase head pressure because its measures in a 1" square area for PSI. BUT, the pump outlet is a specific diameter. Lets use 1" for this example. Now, take the 1" pump outlet and increase the pipe size to 4" for the rise up to the tank. Now the pump will only pump so much, Right? Should not pump any more GPH with a 1" pipe or a 4" when pipes are run horizontal. BUT. The weight of the water in the 4" pipe is much heavier than the 1" for each foot of pipe for the vertical rise. Now, the pump outlet is still 1" diam, even though the 4" pipe. This creates more head pressure at the PUMP because the pump has all the weight of the 4" pipe's water forcing into a 1" pipe. It's Hydraulics principle. The reason Hyd cylinders can have so much force with a little power input.

Sorry but you folks are incorrect. First off more pressure doesn't mean more flow, yes the smaller the pipe the more pressure, head pressure so less flow. Actual head pressure is only a function of density, height and gravity not cross sectional area. You also however have losses from pipe design which includes pipe friction from pipe diameter, finish, flow regime, and the number and types of fittings used. Bottom line is the bigger the pipe the better as fiction reduces with larger pipe sizes, however you will max out the benefit depending on flow rate.

sphelps · #8 03-17-2009, 10:13 PM

If you folks are still in doubt just try playing around with that calculator on RC, link posted above. You will see that increasing the pipe size can dramatically decrease head pressure depending on flow rate and never will head pressure increase due to a larger pipe size.

BC564 · #9 03-17-2009, 10:21 PM

volume increases....but the head pressure doesnt change......head pressure is the weight of the water vertically only.....unless your running a huge distance or have lots of elbows....which adds head pressure......

27.2inches of water veritcally is equal to 1 psi.

I agree with sphelps

Myka · #10 03-17-2009, 10:25 PM

Quote:

Originally Posted by sphelps

Sorry but you folks are incorrect. First off more pressure doesn't mean more flow, yes the smaller the pipe the more pressure, head pressure so less flow. Actual head pressure is only a function of density, height and gravity not cross sectional area. You also however have losses from pipe design which includes pipe friction from pipe diameter, finish, flow regime, and the number and types of fittings used. Bottom line is the bigger the pipe the better as fiction reduces with larger pipe sizes, however you will max out the benefit depending on flow rate.

I didn't say more pressure increases flow! Where do you see that? A person will get less gph, but more psi at the end of a 1" pipe than using the same pump on a 3" pipe.

This is the same principle for powerheads which an impeller produces less gph, but more pressure, and a propeller produces more gph, but less pressure. How a MJ1200 with 198 gph will blow the flesh off certain corals placed 4" away where a Koralia 1 with 800 gph won't.