Science Question

[lilrobb]

So let's say I have a 1/2 pipe standing upright and a maxijet on the bottom - I can determine the max head pretty easy by measuring the height of the watercolumn in the pipe.

What happens when I use 4" pipe now, will the pump reach the same head height, more or less?

(my point of view - where I differ from a dear friend is the following:

The water column in a 1/4" pipe has a weight of x lbs pressing down on the pump, a pipe with 4" diameter has significantly more water (weight wise) to carry so the back pressure on the pump will be more, hence it will reach less head height,)

Scientifically proven comments?

 

[sharkbait]

You are correct Rob, the larger the diameter of the pipe the more weight/head pressure. So if you were to use the maxi-jet on the 4" pipe you would get significantly less height then with the 1/2" pipe. Most pumps have a pipe total diameter size on them to indicate for this very reason.

 

[acroholic]

Here is a link for a pond site that has a pretty good section on calculating maximum head pressure needed for pond systems. Look at Table Two and the text down to where Table Three starts, and it comments on flow and head height related to pipe diameter and pump rating.

 

[morganatlanta]

But you will have less drag on the main flow than you would have had with 1/2" pipe, so there's that to consider as well....

 

[grouper therapy]

Sharkbait;680231 wrote: You are correct Rob, the larger the diameter of the pipe the more weight/head pressure. So if you were to use the maxi-jet on the 4" pipe you would get significantly less height then with the 1/2" pipe. Most pumps have a pipe total diameter size on them to indicate for this very reason.

Wrong

 

[lilrobb]

Here comes my challenger!

 

[grouper therapy]

blixem;680286 wrote: Technically the weight is the same on both pipes at the same height, the difference is the weight is not distributed across the same area. You would be concentrating the 4" area of weight into 1/2".

Sharkbait is correct, but it's even worse than the weight issue. You also have to take into account the output on the pump is set for 1/2" and even with a 4" adapter to it, the stream of water going up the pipe is not going to be evenly distributed. The majority of the flow will be in the center 1/2", which means that there is also non-linear pressure pushing against the main stream. This will cause turbulence in the flow, introducing a whole new set of fluid dyanmics problems.

wrong

 

[crew]

It's simple.. Pascals law states that pressure remains constant while flow rate changes.

That is in relation to a change in pipe diameter.
Easy peasy

 

[lilrobb]

Acroholic is next, and his table reference looks pretty good to me...

Edit:

Crew;680350 wrote: It's simple.. Pascals law states that pressure remains constant while flow rate changes.

Easy peasy

Okay,

so that means at a certain height flow would be ZERO, correct?

 

[crew]

Yes, and the zero would be the head height that you previously reached.

Let's say your pump gets water to a height of 4 feet. What you aren't considering is how fast it got there. That's where your flow difference will be apparent. With the 1/2 pipe it might take 10 seconds, while the 4" pipe takes 1 minute

The height is still 4 ft

 

[grouper therapy]

Taken from Danner site(magdrives)




How do I know what my Head Height is?
There are 2 parts to the answer. First, the Static Head in a system is the height in feet from the surface of the water the pump is sitting in to the highest point it is pumping to. It doesn’t matter how deep the pump sits in the water, since it is only working when it is raising water up from the original level. Next, the friction or resistance added by the pipe and fittings the water must flow through is the Friction Head, which is added to the Static Head to get the Total Head. You can keep your Total Head as low as possible, maximizing the flow from your pump, by keeping the friction losses in the plumbing as low as possible, usually accomplished by using as large a diameter pipe and fittings as possible.
What size tubing do I need?
Generally speaking, the typical back yard water garden has a low Static Head (see above), that is, the waterfall is usually between 1&#8217; and 10&#8217; in height. If your pond falls into this category, you can take advantage of very efficient MagDrive and HY-Drive pumps which require very little electric to produce great flows at low heads. The catch is, you&#8217;ll want to move the water through relatively generous pipes or tubing so your pump is just lifting the water to your falls without having to work against a lot of friction in the plumbing. These are the recommended maximum flows per given diameter of pipe so your pump is just <u>lifting</u> water, not <u>forcing</u> it through restrictive plumbing.

 

[lilrobb]

Crew;680355 wrote: Yes, and the zero would be the head height that you previously reached.

Let's say your pump gets water to a height of 4 feet. What you aren't considering is how fast it got there. That's where your flow difference will be apparent. With the 1/2 pipe it might take 10 seconds, while the 4" pipe takes 1 minute

The height is still 4 ft

So the table2 in Acroholic's link is wrong?

Edit:

grouper therapy;680356 wrote: Taken from Danner site(magdrives)




How do I know what my Head Height is?
There are 2 parts to the answer. First, the Static Head in a system is the height in feet from the surface of the water the pump is sitting in to the highest point it is pumping to. It doesn’t matter how deep the pump sits in the water, since it is only working when it is raising water up from the original level. Next, the friction or resistance added by the pipe and fittings the water must flow through is the Friction Head, which is added to the Static Head to get the Total Head. You can keep your Total Head as low as possible, maximizing the flow from your pump, by keeping the friction losses in the plumbing as low as possible, usually accomplished by using as large a diameter pipe and fittings as possible.
What size tubing do I need?
Generally speaking, the typical back yard water garden has a low Static Head (see above), that is, the waterfall is usually between 1’ and 10’ in height. If your pond falls into this category, you can take advantage of very efficient MagDrive and HY-Drive pumps which require very little electric to produce great flows at low heads. The catch is, you’ll want to move the water through relatively generous pipes or tubing so your pump is just lifting the water to your falls without having to work against a lot of friction in the plumbing. These are the recommended maximum flows per given diameter of pipe so your pump is just <u>lifting</u> water, not <u>forcing</u> it through restrictive plumbing.

That would be an F in school - good answer, but not for my question... LOL

 

[grouper therapy]

Crew;680355 wrote: Yes, and the zero would be the head height that you previously reached.

Let's say your pump gets water to a height of 4 feet. What you aren't considering is how fast it got there. That's where your flow difference will be apparent. With the 1/2 pipe it might take 10 seconds, while the 4" pipe takes 1 minute

The height is still 4 ft

Thank you The larger pipe actually reduces the total dynamic head by reducing the head derived from friction.

 

[lilrobb]

See here:
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<legend> Attached files </legend>

 

[crew]

No, acroholics table 2 is correct. Notice they are separated by flow rate. Let's say pump a pumps 100gph at 5ft vertical with a 1/2" line. With a 4" line, it will still pump 5th vertically, just not at 100gph

You will eventually reach a height that the 4" line can't pump, but the smaller line won't be able to hit that either because of frictional forces, more specifically the 3rd law of friction. Two different forces are keeping the water from reaching the same height.

Pressure is constant
Flow is not

 

[lilrobb]

table 2 my friend, you're looking at 1

It says that a 600gph pump does 7.8' of head with 1/2" pipe but only 0.15' at 1.25" pipe

 

[grouper therapy]

<span style="font-family: Comic Sans MS, Arial, Helvetica">This from the chart that acroholic posted! I don't think it contradicts what we are saying.Maybe in redneck German!
So according to the above table, if we have 30 feet of pipe, and a flow of 3,333 GPH, the pump head due to the pipe alone, without any fittings, would be 4.22 * 3 = 12.66 feet of pump head for 1 ¼ &#8220; pipe; 1.99 * 3 = 6 feet for 1 ½ &#8220; pipe; 0.58 * 3 = 1.7 feet for 2&#8221; pipe, </span>

Edit:

LilRobb;680363 wrote: table 2 my friend, you're looking at 1

It says that a 600gph pump does 7.8' of head with 1/2" pipe but only 0.15' at 1.25" pipe

exactly
Less head = more flow duh

 

[crew]

I'm looking at right table. If you want a flow of 600gph you can go up 7.8 feet for the smaller or .15ft for the bigger pipe. That doesn't mean it's not going to reach that height eventually.

Edit: The bigger diameter will still reach 7.8 ft, but it won't be at 600gph

 

[grouper therapy]

The larger diameter pipe produces less friction thereby reducing the total dynamic head loss thereby increasing the gph for the pump assuming same vertical lift.

Edit:

Crew;680366 wrote: I'm looking at right table. If you want a flow of 600gph you can go up 7.8 feet for the smaller or .15ft for the bigger pipe. That doesn't mean it's not going to reach that height eventually.

Edit: The bigger diameter will still reach 7.8 ft, but it won't be at 600gph

That is not what it is stating. both would have the same vertical lift. The.15 represents the less head loss representied vertical lift

 

[lilrobb]

Well, I guess you can interpret the table both ways - you take the flow as a variable, and the height as fix - I take the flow as a fix and the height as variable.

I hear you - Dave, don't you have a stand to build?

And Crew, thanks for posting here - I love learning new things.

(I still down't believe a maxijet will will 1 4" pipe even 4' before crapping out - but that will have to be proven by experiment... stay tuned.)