The one where CW and GBBUDD argue about pipe sizing.

[combatwombat]

So, @GBBUDD and I were looking at our tubes the other day and arguing about whose was bigger and whether it mattered. Then we realized we were making a mess of a new member's thread, and moved over here.

At the crux is this question: Is it pointless to plumb your pond with piping that is larger than your pump's outlet?

For example: You have a pump with a 1-1/2" outlet. Or your skimmer has an outlet port that is 1-1/2". Should you use 1-1/2 pipe in your pond?

Is there ever a benefit to increasing pipe size to 2", or is the 1-1/2" outlet on your pump/skimmer box a restriction that cannot be overcome?

In the next reply, I'll copy over the conversation from the other thread.

 

[combatwombat]

If your outlet is 1 1/2 it makes no sence to go larger you could put a 6 inch line up to the 1 1/2 and it's still only has the volume to push through of the smaller.

How are you unsure? you cant push through a 1 1/2" pipe the same amount of water that a 6 inch or for a closer reference even a two inch line can push. your max will only be what ever the smaller pipe is. sure you cant jack the pressure but equal pressure to both and 2 inch wins everytime

That's correct, but we're not talking about equivalent lengths of pipe. The factor is only the size of the outlet of the skimmer, which is a small part of the whole pipe system.

The way I read your post is that whatever size outlet you have on your skimmer, pump, whatever—that's the size pipe you should use because anything else would be pointless.

Many (maybe even most) pumps I've seen up to about 7,500 gph have a 1.5" outlet. If I wanted to deliver 6,000 of those gph to somewhere 100' away, should I use 1.5" pipe or upsize to 2"? Or even 3"? I've never seen pond pump or skimmer with a 3" outlet, but 3" pipe is used all the time because it reduces head loss over long distances.

Apologies if I misunderstood what you were saying.

that's correct no matter how you slice it yes . going to a 3 inch after a 1 1/2 pipe is a waste of money you can throw as much psi at it as you want a 1 1/2 pipe can't handle even a third of what a three inch can

Well, I'm not sure what else to say other than that is not correct.

Ok, actually that part is correct, but it is not applicable to what I'm talking about and what [OP] needs to know to understand friction loss in their plumbing system.

@GBBUDD: Don't you run 3" lines in your own pond? I saw a photo of you washing pea stone with a 3" flex pvc hose?

I'm trying to figure out if we're arguing the same point here, because I'm baffled. Ponds are built every day w/ 3" pipe. I've never seen a pond pump or a skimmer that has a 3" outlet unless it was modified. Do you think it's pointless to use a 3" pipe on a pump with a 2" outlet?

One small restriction doesn't eliminate the benefit of a larger pipe. It just adds some friction to the overall equation. You wouldn't run 10,000 GPH through a 1.5" line, but a 1.5" outlet on a skimmer doesn't keep you from running 10,000 gph at all. It means you have to compensate for it somewhere else in the system. Like a bigger pipe!

It's just a matter of how much head pressure you're able/willing to deal with. Theoretically, if you have a strong enough pump, you could send 50,000 gph through a 1/2" pipe. Not really as the pipe would probably explode, but the physics allow it.

The restriction that an undersized fitting or inlet/outlet makes is not a showstopper. Seems that pretty much every pond over about 5,000 gallons would have at least one. They're just restrictions that increase the power needed to push the amount of water you want.

YES that is correct. but the difference is my pump has a 3" inlet and a 3" output not a 1 1/2
YES aLL GOING TO A 3" IS GOING TO DO FOR YOU IS INCREASE HEAD"the amount of water the pump will have to push will double" yet the pressure reduces by more than half it can only push from the restrictions of a smaller pipe it can never give what the larger pipe is capable of AT THE SAME PRESSURES. COULD I TAKE A 1 1/2 " LINE separately pressurize it it to 3000 and get the same flow out of it that a 3 inch can at 40 spi i believe so but thats is only relevant to a point . Because you still only have the restriction of a smaller pipe at the start . Now fluid dynamics is an art all by it's self but having talked to engineers over the years and way to many of them, they factor in some ridiculous things like flex on a 15 foot WIDE concrete caisson. 50 feet deep. how much is a concrete cylinder going to bend REALLY. Can you increase the pressure of a 1 1/2 inch pipe to 3,000 psi and really push some fluid through it sure. are you getting again anything over a 3" nope throw the same 3,000 psi to a 3" and your pond will be empty in a minute.
U can certainly reduce from larger to small every day of the week you'll reduce flow and pressure each time you add another branch off the LARGER supply that's why we add ball valves to control who gets how much of that pressure and flow.

yes we are talking the same animals but your increasing pressure to pipes the same pressure both fed through a smaller pipe will have the restrictions of the smaller pipe throughout the system . you gain nothing" if i took my 3" outlet and reduced it to 1 1/2 my pressure will skyrocket because my pump is being restricted is it still going to put out through the 1 1/2'' pipe the same as it were the three inch AT THE ORIGINAL PRESSURES "HEAD" no but . Thats where fluid dynamics come in, AND ONE OF THE MOST COMPLICATED ENGINNERINGs THERE IS. "sorry for caps its just me.''

YOU NEVER WANT to intentionally reduce a pipe inline and then step back up to the larger for no reason. you will severely reduce your flow . don't make it confusing,. To answer to the question by the post is if you have 1 1/2 inch as a feed from your pump stay with that size you get no benefit increasing the pipe size in our simple plumbing designs.

 

[combatwombat]

To further my own argument:

Upsizing pipe is commonplace.

It is common knowledge that you can reduce the head loss in your plumbing system by increasing pipe size, regardless what fittings come on your pump/skimmer/filter/whatever. It's done everyday by pond builders all over the world. I don't believe they are all wasting their money and energy.

Large pumps routinely come with small ports.

Sequence—one of the biggest pond pump manufacturers in the world—produces all kinds high flow pumps with small discharge ports. Here's one of their 11,000 GPH pumps with 1-1/2" suction and discharge ports. All over the internet, you will find charts stating that a 1-1/2" pipe can carry a maximum of 3,600 GPH. It seems @GBBUDD would argue that the best this pump can do is 3,600 GPH. Does that make any sense?

Pump engineers would seem to agree with me.

If you google "what size pipe should I use for my pump" you'll find lots of blog posts and resources from pump engineers. Here's a quote from this article, published by Crane Engineering:

In terms of diameter, discharge pipe diameter should normally match the discharge flange on the pump but can be larger to reduce friction losses and decrease system pressure. On the suction side, the diameter can be the same size, but oftentimes engineers select a size or two bigger, thus requiring an eccentric reducer. Larger suction piping on the suction side is usually preferred if the liquid viscosity is greater than water. This also helps produce an even flow to the pump and avoid cavitation.

 

[addy1]

Lol gentle disagreement......I have never worried about it use two inch for all fittings. Pump has 2 inch connections.

 

[GBBUDD]

Good grief ! is it done yes should you on a simple pond design thinking youll get any benefit from a now larger pipe NO ..can you sure if no other parts are available go for it
Talk about beating a dead horse ok i'm wrong do as you'd like .

 

[TheFishGuy]

I would say it is better for future upgradeability. If I want to up my flow in two years I need larger pipes to handle that flow, and it would be easier to install them at the time of initial construction.

 

[combatwombat]

Good grief ! is it done yes should you on a simple pond design thinking youll get any benefit from a now larger pipe NO ..can you sure if no other parts are available go for it
Talk about beating a dead horse ok i'm wrong do as you'd like .

It's not a dead horse. Pipe sizing is a critical part of a pond plumbing system since, as you know, every inch of additional head pressure reduces flow. The argument you're making directly contrasts everything I've read about how these low pressure plumbing systems work, so it seems a pretty important point to nail down.

If you're right, then pretty much everyone—including anyone who buys a high flow pump with a 1.5" or 2" discharge port—is wasting money and not getting a fraction of the flow they think they are.

What do you make of these Sequence pumps delivering 11,000 GPH from a 1.5" discharge port? How is that possible from your point of view?

 

[Rabungalow]

This is how I see the situation. If you have a network modem that is providing 100GB of bandwidth and then connect a network cable with 10GB throughput to your network router that is capable of 100GB. The best bandwidth you will ever get on your router is 10GB. I would assume the same would apply to flow rate on a pipe if at any point there is a bottleneck.

 

[combatwombat]

This is how I see the situation. If you have a network modem that is providing 100GB of bandwidth and then connect a network cable with 10GB throughput to your network router that is capable of 100GB. The best bandwidth you will ever get on your router is 10GB. I would assume the same would apply to flow rate on a pipe if at any point there is a bottleneck.

That’s a relatable analogy, but—at least as far as I understand—not how water works in a pipe. The restriction of a fitting adds dynamic head pressure to the system. The more flow you are pushing, the more dynamic head it adds. But it doesn’t put a physical limit on how much water can be pumped through the system because there is no true physical limit to how much wate can flow through a pipe beyond the burst pressure of the pipe itself.

I think the wide array of 10k+ GPH pumps with 1.5 and 2” ports is a testament to that. If it worked like a network cable, then every pump over 3,600 GPH with a 1.5” port would only be capable of delivering 3,600 gph.

That’s obviously not what’s happening, right?

 

[Jhn]

Guess I will answer here since was tagged in the other thread. I was told by all the plumbers I have worked with, was that as @GBBUDD said it doesn’t matter what you use after a smaller pipe water can only be forced through that bottle neck so fast. Not a plumber or an engineer, just what I have been told by numerous plumbers.

@combatwombat while it is important to get pond volume turnover correct, (ie close) to say it is critical to nail it down, I disagree, with that. It Really isn’t unless you are going for a DKP. natural/eco ponds not so much, have never tried to or cared to figure out exactly what is flowing through my ponds. It is generally in the area, of what it needs to be, I know this because have never had an issue with my setups in over 25 years of being in this hobby.

 

[Rabungalow]

@combatwombat

I found this piece on South Austin's irrigation website.

"Too many people–even some industry professionals–believe that using progressively smaller pipe sizes in a lawn sprinkler system will help keep the water pressure high. The argument goes something like this: if water moves through the pipes and past the sprinklers, the pipe should get smaller in order to squeeze the water so that the pressure stays high enough to operate the sprinklers. However, this is not the case.

This misconception largely persists because the reasoning behind the argument seems logical and tallies with experience. For example, when you put your thumb over the end of a hose, you make the opening smaller; and as you do so, you can feel the water pressure behind your thumb increase. This would seem to be proof positive that decreasing the size of an opening increases water pressure and that, by extension, a smaller pipe would also do the same thing.

But the reality is that when you put your thumb over the end of a length of hose, you’re only changing the flow dynamics in the hose. When water moves through a conduit of any kind, it encounters resistance caused by conduit surfaces. But it still moves at the maximum speed possible while still overcoming this friction. When the water leaves its conduit, it has almost no pressure left.

What all this means is that when you put your thumb over the end of the hose, the water flows more slowly, resulting in a loss of pressure due to friction. The more tightly you squeeze your thumb, the more you’ll see reduced flow and feel greater pressure. But the bottom line is, you’ve not created any new pressure. You’ve just made a trade-off (reduced flow for increased pressure)."

The last piece in blue is what I found to be the kicker. You are reducing the flow for increased pressure.

 

[combatwombat]

Guess I will answer here since was tagged in the other thread. I was told by all the plumbers I have worked with, was that as @GBBUDD said it doesn’t matter what you use after a smaller pipe water can only be forced through that bottle neck so fast. Not a plumber or an engineer, just what I have been told by numerous plumbers.

@combatwombat while it is important to get pond volume turnover correct, (ie close) to say it is critical to nail it down, I disagree, with that. It Really isn’t unless you are going for a DKP. natural/eco ponds not so much, have never tried to or cared to figure out exactly what is flowing through my ponds. It is generally in the area, of what it needs to be, I know this because have never had an issue with my setups in over 25 years of being in this hobby.

I’ve heard the same, but but plumbers are typically talking about household plumbing fed by municipal, relatively unchanging water pressure. It makes more sense in that application. As far as I can tell, that’s still wrong, but closer to reality in household plumbing.

You can easily test that by timing a 5 gallon bucket fill from a hose and then doing so again after turning the nut in your pressure reducing valve. It fills faster/slower based on the pressure you set.

You’re right that in a lot cases we’re splitting hairs, but in a lot of other cases we’re talking about giving out phenomenally bad advice that either wastes lots of money or doesn’t deliver the desired flow.

Let’s go back to that 11k GPH pump from Sequence (and many others) with a 1.5” outlet.

If we believe that the smallest fitting in a plumbing system sets the maximum flow rate, then we have to believe that this 11,000 GPH pump can only deliver 3,600 GPH of flow, wide open with no hose attached.

Do you believe that to be true? That’s the basis that this argument is built on.

 

[combatwombat]

@combatwombat

I found this piece on South Austin's irrigation website.

"Too many people–even some industry professionals–believe that using progressively smaller pipe sizes in a lawn sprinkler system will help keep the water pressure high. The argument goes something like this: if water moves through the pipes and past the sprinklers, the pipe should get smaller in order to squeeze the water so that the pressure stays high enough to operate the sprinklers. However, this is not the case.

This misconception largely persists because the reasoning behind the argument seems logical and tallies with experience. For example, when you put your thumb over the end of a hose, you make the opening smaller; and as you do so, you can feel the water pressure behind your thumb increase. This would seem to be proof positive that decreasing the size of an opening increases water pressure and that, by extension, a smaller pipe would also do the same thing.

But the reality is that when you put your thumb over the end of a length of hose, you’re only changing the flow dynamics in the hose. When water moves through a conduit of any kind, it encounters resistance caused by conduit surfaces. But it still moves at the maximum speed possible while still overcoming this friction. When the water leaves its conduit, it has almost no pressure left.

What all this means is that when you put your thumb over the end of the hose, the water flows more slowly, resulting in a loss of pressure due to friction. The more tightly you squeeze your thumb, the more you’ll see reduced flow and feel greater pressure. But the bottom line is, you’ve not created any new pressure. You’ve just made a trade-off (reduced flow for increased pressure)."

The last piece in blue is what I found to be the kicker. You are reducing the flow for increased pressure.

I’m no irrigation pro (never even installed a sprinkler), but that all makes sense to me. I don’t think I'm seeing how it fits with what you said earlier, though.

 

[Rabungalow]

@combatwombat what I believe this to be explaining is that if you are reducing the pipe at some point you are reducing the flow-rate at which can be passed. So if you have a 10,000 gallon pump with a 2inch outlet and and some point you reduce your plumbing to 1-1/2 then you will not be getting the full 10,000 gallon flow-rate and in addition be adding the additional wear and tear on your pump due to the pressure increase.

 

[combatwombat]

@combatwombat what I believe this to be explaining is that if you are reducing the pipe at some point you are reducing the flow-rate at which can be passed. So if you have a 10,000 gallon pump with a 2inch outlet and and some point you reduce your plumbing to 1-1/2 then you will not be getting the full 10,000 gallon flow-rate and in addition be adding the additional wear and tear on your pump due to the pressure increase.

Yes, totally in agreement. But I’m talking about INCREASING pipe size beyond the outlet of the pump to achieve more flow in the same length of pipe. So if you have an 8,000 GPH pump with a 2” outlet and you need 6,000 GPH to come out of a waterfall 100 feet away, should you use 100’ of 2” pipe that will add 15’ of dynamic head on its way there or 3” pipe that will add about 2’?

That’s a trick question of course because we don’t know anything else about the pump. But it illustrates my point.

In your example, a 10,000 GPH pump with a 2” outlet shouldn’t exist because every engineering flow chart says 2” has a real world max flow of about 5,400 GPH.

But 10,000 GPH pumps with 2” outlets are sold all day every day…