Plumbing question
 

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

You, sir, are correct!

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

No sir, you are not correct :mrgreen:

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!

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.

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.

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.

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.

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.

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

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.

I agree with you.....but that is something different ......your putting the same volume through a smaller pipe....which increases pressure...

I thought we were just talking about head pressure ???????

[quote=Myka;400466]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.
QUOTE]

Put a pressure gauge at the end of each pipe and it will be the same.

I can see where I got screwed up. The volume increases in the larger pipe. and pump only displaces a certian amount of water. Ya the larger pipe will not add anything to head pressure. Like the difference in a drain. Take a 40g tank, and a 140g tank, both of same height. Drill a 1" hole and install a bulkhead in it. Think of the tank as the larger pipe. more volume, right. Which would have more pressure at the 1" bulkhead? Neither

I was kinda thinking backwards in my previous post. It doesnt matter how large the pipe is, the pump is only pushing put it's amount of water, regardless. When working on gravity, water falling down a pipe, then the PSI gains as the pipe narrows due to the velocity of the water, not just head pressure.. Principal behind Hydraulic strip mining

Well you started off your post by saying you agreed with the fact that larger diameter pipe means more water weight and therefore less flow. Your next statement seemed to be your argument on why you agreed. Sorry for the confusion but I'm not a mind reader :biggrin:

You guys should listen to Sphelps on this matter or he may just go Bernoulli on you.

No it won't be. The pump will be restricted by the decreased flow out of the end of the pipe...the same reason fittings on a pipe decrease pressure. Now, if you close the end of the pipe you would be right.

Bernoulli, LMAO. Were not building plane wings here :lol:

I think you're getting confused. Decreasing the pipe diameter will increase back pressure at the pump, but I don't think you can use it to increase PSI at the outlet that way. Think of the applications for that kind of technology :wink: Perhaps you're thinking of velocity? I'm not sure what that has to do with head pressure though, which is influenced by gravity, not a pump.

If we take a 5" pipe and adapt it to a 3/4 opening in the pump, the weight of the water in the pump is only the area of the 3/4" opening times the weight of water. The rest of the weight, 4.5" will exert force on the adapter.
As sphelps says, use the calculater in the link above, as the pipe dia. increases, head pressure goes down.

So that we are are clear on this question, if the pump on the left has reached its maximum head, it would be the same height as the pump on the right with a much larger diameter?

haha, only as a last resort :wink:

Bernoulli's equation can be used in all kinds of fluid mechanics, including pipe flow.

:biggrin:

As said big is better for pipe runs and loss due fittings, why I stayed with 1.5" to the bottom of my display.

What I wish for is a calculator that would take into account various line sizes (I'm running a 1.5" return line from the pump but then reduce to 1" at the display bulkhead).

Hard to believe isn't it, but it is true.

Maybe I'm not being clear about what I mean, or maybe you're wrong. :lol:

We use say 1200 psi to go through a 5/8" hose then through a 1/8" fitting on the end (we use this on Hydro-Vac trucks to cut the ground), and voila! It will cut your toes off. If we use 1200 psi pumped through a 3" hose (which you would never be able to hang onto, and you'd need a muuuuuuuch bigger pump to get 1200 psi out the end of a 3" hose), and you wouldn't hurt your toes with it.

So...slap your fancy words (pressure, head pressure, velocity, psi, flow, whateeeever) on that equation, and tell me what the heck you mean that I am wrong. :eek:

I think the pump comes into play here, I agree with what you can do to cut my toes off (God forbid) but you are using a positive displacement pump that doesn't know the meaning of the word backpressure, a typical aquarium pump doesn't come close to 3 psi and simply doesn't do what a hydraulic pump is capable of, in effect you are both right.

Adding a nozzle will increase dynamic pressure within the nozzle and increase the head pressure on the pump, but this will result in less flow on a centrifugal pump. In addition as stated positive displacement pumps are not effected by head pressure, they pump the same amount of fluid no matter what. Of course they do have a maximum operating pressure before something blows up which is why such pumps will have a release valve for safety.

You can't relate such systems to aquariums, we use centrifugal style pumps where head pressure is relevant, I'm actually pretty confused on what you argument is at this point :confused:

LMAO!!! :lol:

I give up on you, you aren't understanding.

But were not changing the pump. What would your 1200PSI pump out out with a open 4" hose, No nozzle. I guarantee you it wont be 1200PSI. But it still woould take your toes and whole feet off if it was exiting the hose at 1200PSI

I'm not acctually sure where this is going anymore, but head pressure is irrelavent of the volume, its height. Thats the main reason why our tank glass gets thicker the higher the tank gets. Higher water, more pressure. Regardless of vessel size. Just like pressure in the Ocean at 15ft below, is the same as in a pool at 15' below. Head pressure has nothing to do with flow or anything. Its just the weight of a column of water.

Ooooooh but that was my point!!! If it's 1200 psi out of a 1/8" nozzle, it ain't gonna be 1200 psi out of a 4" tube.

Illustration and graph,
http://home.earthlink.net/~mmc1919/venturi.html

If it's on the internet, it must be true.

Myka, think your need to separate pressure and flow as they are not the same thing. As for your vac truck could have a 4" line with a 1/8" nozzle and it still would probably take your toes off with the orginal pump. Reason you wouldn't have a 4" line is having to drag around the weight of the water in the hose.

OH. LOL I had to many beers last night

Cat urine glows under a black-light :bananalama:

But back to the basic question. Does head pressure change at the pump, when using larger diameter pipes for tank return.

NO, it remains the same. The pressure the pump see's is equivalent to the weight of water equaling the volume of a pipe the same diameter as the pump outlet, times the head height.

Now as far as friction losses, they are regardless of head height. Friction losses will happen on horizontal runs as well as vertical. If said pump was loosing flow (GPH) due to frictional losses, then yes, upping pipe size can gain back some lost GPH.

Heres a chart comparing firehose sizes and friction losses per 100' of hose. Distance and flow determine friction losses, not head height



Losses in PSI of firehose per GPM flow @ 100 PSI pump pressure

1.5" diameter
GPM/ PSI Loss

50 6.3
100 25
150 56.3

2" diameter

50 1.7
100 6.6
150 14.8
200 26.3
250 41.1
300 59.2

2.5" diameter

150 4.9
200 8.7
250 13.5
300 19.5

And for elevation, add 0.5 PSI for each foot

Here I thought the original question was well answered already, and that we were delving off further into the topic...???

lol, I'll shut up now

BTW there is no head loss in a closed loop :)

What tends to happen when people figure out they're wrong is they go on and on about something completely irrelevant as a means to justify their original statement. We can't always be right so when we're not we should just cut the BS and admit it :mrgreen: