Does Size Really Matter? - Water Supply Pipe Flow Rates
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- Опубліковано 13 чер 2020
- www.homebuildingandrepairs.com... Click on this link for more helpful information about plumbing, new home construction and building repairs. Here's another video that will blow your mind, when you find out how much volume of water can flow through different sized plumbing pipes. The examples in the video will include different sized pipes, along with the area of those pipes and flow rates. It really is amazing to think about how much water can come out of some of these larger pipes.
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Learned this same lesson 20 yrs ago. lol. Now I can send your vid to people that want me to explain it instead of doing it myself. Thanks
That's funny.
I learned this making exhaust systems for cars where people often way oversize their tube diameters for the flow they need.
I think the reason why the relationship between pipe cross sectional area and volumetric flow rate is not linear is because of the energy losses (frictional head losses) that occur along the pipe wall as water moves along it. The greatest amount of friction is at the wall where water touches the pipe so velocity there is smaller compared to the center of the pipe where water has little resistance and can move faster. Different pipes probably have different roughness values.
I was about to post this. You are absolutely correct. Wall friction is the exact reason why this occurs and 2 4in pipes flow less than a 1 8in pipe.
I dunno. Real world vs real world. I ran a 4,768 foot 1” line off a 1” meter. At meter the psi was 175psi. Guess what the psi was crossing 2 hills and continued the 4768’? 🤫 175psi using pex. Sorry to dispute the charts. But I’ve run across 3,000’ lines where they claim an engineer told them to put a 2” line behind 3/4 meter. And that will maintain flow. Say what you want sitting there never tried it. But the meter pressure started around 135. Guess what I tested at 100’? 100psi. Then at the house over 500’ away. ? 45psi. Dumbass said “good thing I ran 2”. 🤦🏼♂️ so I bet him $2500tl pay for new 3/4 pex just to tickle my fancy. He jokingly agreed. How could s plumber have real world results contrary to engineer? But so after got done. Guess what I had at house top floor shower? 😂 yeah 135psi. Used the 2” to sleeve the 3/4. He was amazed to see the garden pressure touch the top gutter. Said he’s lived with low pressure for 18 years.
That plays a part. But it's just down the the area. I mean he explains it in the video... if you had a 10 inch pizza and upgraded to an 11 inch. You'd gain significantly less pizza than someone upgrading from a 20 inch to a 21 inch. When you look at the area gain like that, from the outer part of the circle is might be easier to visualise
One of the most informative videos I can actually put to practical use. Thank you so much for posting this.
Great to hear!
Me too, I was working on a hydronic boiler and when on without thinking to install 3/4 pipes into the boiler and couldn't for the life of me figure out why the boilers PRV was blowing water. The preview pipes where 1/4 inch
Amazing. Thanks for the video.
Glad you liked it!
I went through this a few years back trying to explain this to a worker. Without getting into a bunch of math for square area, I finally summed it up and asked him 'for example, how many 2x2s are there in a 4x4'. His first response was 2, which of course is wrong. I told him there were 4. It kinda works the same way. If you want to talk about volume. Give a video about restriction in PVC fittings
For years I delivered pressure washers to customers in a rental business. The intake had to be 2 inches or the pump would shut off. The pressure was 20 k. For cutting. The engine was a Cummins diesel. Many customers tried 4 or 5 garden hoses. Biggest problem I experienced,, ‘wouldn’t believe me. A 2 inch hose drawing from a full 50 gallon barrell worked fine, and a running garden hose placed in the barrell was sufficient to replenish water being used! At startup about half of the barrel drew down but the single garden hose then kept up with up with usrage
Where do you get 2" hose like that?
Do they have threading r is it all couplers?
I have tried to find flexible 'garden hose" type hose for a rain barrel for years but all the two inch hose I find is pretty expensive and meant for high pressure applications and also has couplers on them that I have never figured out where to get a bulkhead fitting to go into the rain barrel with.
I use a 5/8" hose now but it gets clogged easily and doesn't clear the water fast enough when it rains hard.
Very detailed information thanks 😊
So nice of you
Very informative and enlightening.
Glad you think so!
Wow this was exactly what i was looking for ty!
Awesome.
I appreciate your videos and this isn't meant to be criticism; just asking for more of your clearly communicated and useful videos. Because this material is not necessarily intuitive, it might be helpful to explain why these differences occur. For example: The area of a circle changes with the square of the radius. (Pi * (r^2)). So the first thing to realize is that the difference in area between a 1/2” pipe and a 1” pipe is the difference between 0.5^2 and 1. Since 1/2 squared is 0.25, the difference in area between a 1/2” pipe and a 1” pipe is 400%.
But there’s more. The flow rate of water through a pipe (at fixed pressure, length, and pipe material) is also affected by friction. When the water flow becomes 60% +/- of the theoretical capacity of the pipe, the effects of friction (water against the pipe’s walls) reduce flow rate. So there are two non-linear factors: the pipe diameter and friction.
Also, some examples of where this topic is relevant would also be helpful, say in home repair. For example, if you have an old house with 3/4” copper plumbing, and you re-do a 100’ line to a bathroom that terminates with 1/2” fixtures, do you use a 1/2” PEX connector to the copper or a 3/4” connector? With 1/2” PEX, you might find a noticiable drop in shower pressure - as much as 1.4 gal/min. Why? Two parts. First, copper to PEX has an inherent difference in flow based on interior diameter of about 20% (lower in PEX) because the interior diameter of PEX is slighly lower than in copper. Since the cross sectional area uses the square of the interior radius, there’s a bigger difference than you might imagine. Second, a drop from the 3/4” copper interior diameter based flow rate to the 1/2” PEX rate is even bigger: 3/4” copper has a cross sectional area of 0.436 sq-in and 1/2” PEX is 0.185 sq-in. So wow, that’s a really big difference. In a really short run the impact would be less visible to the home owner: 3/4” pex to the bathroom, then convert to the fixtures. You’ll say, “of course,” but this is just to illustrate the concepts.
Although it is a bit complex, you might want to talk about the Hazen-Williams equation which is an empirical (i.e., based on observing things, not theoretical) formula for flow rates that includes the affect of different pipe materials (which affect friction). (It has limitations based on water temperature and degree of turbulence.) Just for example, the “roughness coefficient” (think friction) of PVC is 150 compared to 130-140 for copper, and the cast iron you might find in a very old house’s sewer system could be 64-83. Which may help explain sizing decisions on renovations.
I wouldn't be offended by a comment like yours, because it offers constructive criticism.
Would love a video explaining how to calculate flow rates for distance and elevation
I will put it on my list.
I'm thinking of installing some vintage lead plumbing in my home. I feel that tap water tastes better that way. It has a clean taste. Would I want a water softener with lead plumbing if my water is moderately hard? Would you consider making a video about this topic? Thank you. Your videos have been very helpful.
I'm assuming this is a joke post but lead pipe may insulate better than copper and PEX keeping drinking water colder out of the tap. Thick wall Aluminum would have a similar insulating effect. Perhaps you could build a heat exchange unit for all the cold water piping to pass through that would cool it.
I was assuming the same thing. Lead is not a common building product today for safety issues.
Very nice video .
Many many thanks
Yes i ran into this at work. A piece of equipment a 6” inlet a supervisor had a manifold made from a 6” pipe with two 3” inlets the problem was it needed 3 3” inlets to work properly. The two 3” inlets causes a pressure drop and cavitation when running the unit at max rate, this cavitation causes the unit to fail on its third job. The supervisor had missed this on a bulletin and was let go.thanks for sharing.
You're welcome and thank you for sharing your story. I realize to most of our viewers who are in the construction industry that it might sound like the supervisor shouldn't of got fired, but when you find out how much money it cost the company to fix something like this, it can make sense quickly.
Hi , hopefully you can help , I am running a main water line from a 3/4 meter at the street to my 3 bd 1b cabin i built , the distance of the run from the meter to the house is roughly 1200 feet - it’s a straight shot now turns or Elbows , from the street to the cabin over the 1200 ft it will go up hill about 80 ft in elevation - what diameter pipe should I run ? From what I have read and learned it looks like 2” will be the best - my only concern is the pressure drop by the time I get to the house . I do residential hvac and plumbing so I am familiar with this , just not at this scale as far as that length of run
I would contact a plumber in your area or ask local building department for advice. If I gave you something and was off by 1/8 of an inch, I would feel horrible.
Thank you very much for the reply , could I contact a mechanical engineer and pay a fee to have them size it ?
@@bortnerfamilyadventures1369 Hello I am a chemical engineer and maybe I could be of assistance. It sounds like you are trying to size your line according to the amount of “head” you have to overcome. I would recommend finding the head your water pump can generate and size it accordingly. 14.7 psi is about 33ft of head (elevation) then you just have to look up “K factors” for the friction your pipe material has and convert that into equivalent head(elevation). You can then size your line accordingly to give you the highest flow. I’d assume turbulent flow but you can learn to calculate that if you so desire and you want to give your pump about 15% error for breathing room.
Likewise, one 6’ wife is better than two 3’ wives. It’s all about friction over an area.
So needed to replace my 1.5 inches sprinkler pressure vacuum but noticed those 1.5 inches are more than double the price (1 inch). Is it OK to connect the main 1.5inches pvc pipe to 1 inch, then connect it to the 1 inch sprinkler pressure vacuum, then from 1 inch back to 1.5 inches pipe? Am I going to lose any water pressure? Thanks
I would contact the manufacture for more information.
Hi,
I'm having water issues at my home since last week. The flow is intermittent and is accompanied by air whenever the normal pressure returns. I suspect someone had taken connection from the main line with a bigger pipe thats why water in the homes that are at the bottom of the street is low and fluctuating. Please let me know if it could be a reason. ??
The only thing I could think of is that some is doing work to the pipes somewhere before it gets to your house. Check with neighbors also to see if they have the same problem.
If I upsize a pipe from 4" to 5" (56% more area), can I increase the length by 56% & still have the same resistance to flow? Thanks in advance, UA-camrs.
Can I have a link to the source of this information?
I did most of the calculations myself, but found some of the information by typing in "water pipe flow charts" into your favorite search engine.
Hello sir, our pipe is 1/2 inch from the source, would there be a changes if i am going to connect atleast 2 length 1 inch pipe and the connect again to 1/2 inch? To simplyfy
Source 1/2 inch pipe connected to 2lenght 1inch pipe then connect again to 1/2inch pipe. (For house hold used)
I've seen things like that done before with good results, but don't be surprised if it doesn't do much.
I am planning on re-piping my house in in type L copper (VERY soon in fact since I have 50 year old galvanized pipe that's not in good condition). I have currently have a 3/4 inch supply coming from the meter, 3/4 inch feeding the clothes washer and water heater, everything else is reduced to 1/2 inch. Am I correct in assuming that I would come off better just running 3/4 to every fixture when I do the re-pipe?
Not always, but if you need the extra water pressure, then go for it. You can always use the old pipe layout and assume that you will have more water pressure, because the old galvanized pipes might be restricting water pressure because they are rusting inside.
This is a good example of why it’s SO much easier to use charts and tables of actual measured water flow in pipes than it is to solve the equations. Humans evolved to have good intuition for linear changes (example 1x1, 2x1, 3x1, etc) but poor intuition for non-linear changes (example 1x1, 2x2, 3x3, ... or 1/1, 1/2, 1/3, ...). The equations for water flow have LOTS of non-linear changes happening at the same time. Actual water flow in real pipes is even more complex (example, is the water moving smoothly in the same direction, or is it turbulent and churning?). In these cases (and others, like pandemic growth rates) our ‘common sense’ intuition fails dramatically.
Obviously this was NEVER meant to replace any type of engineering tables or flow charts, because of the complicated nature of the process.
@gregvancom Agreed - and it was an effective explanation
My meter is 3/4 and I'm trying to run a line for 700 feet for 2 homes. What size of pipe do you recommend?
I would check with the people who you pay your water bill.
If I remember my physics well, resistance increases linearly with length, and it increases by a factor of 4 with radius. And flow is directly related to resistance.
Yes, there is more math involved and thanks for sharing.
@@gregvancom Yes, there is, but the power of 4 relationship to radius is the most critical bit of information. This also comes into play in medicine (my field) and explains why bronchospasm (asthma attack) in a child with small airways is so much more dangerous than the same degree of bronchospasm in an adult with large airways. When a little bit of reduction in airway diameter in an adult could lead to some difficulty breathing, the same percentage of reduction in a child can lead to rapid death. I find it interesting how the same fluid-dynamics that come into play in plumbing and pipe-fitting also come into play in a field so seemingly far removed as medicine.
I am a novice and could use some advice. I have a sump pump that pumps water through a 1.5 inch inside diameter pvc pipe up and out of the house. I connected a 2 inch inside diameter smooth silicone pipe to the pvc pipe at the house to carry the water all downhill to the outside drain.
I live in a cold climate where freezing is common at this time of year. The distance to the outside drain from the house is 75 feet. Is the pipe big enough? How do I keep it from freezing(heat tape vs insulation?). Or do I need to change anything as the water temp is 57 degrees as it leaves the house and it’s all downhill.
I would think the size is right, but as far as the freezing, I won't be much help.
What is the psi used for determining the flow rates of various dia. pipes ?
That is the one thing that varies and if you're looking for a particular PSI for water supply pipes in your area, then you might need to check it with the proper tools and gauges. Let me know if this didn't answer your question or try phrasing it differently.
Can I continue 20mm steel pipe with 25mm ppr pipe on my floor. Can reverse reduction work normally???
I need more details.
@@gregvancom i have main steel galvanized pipe led to my floor wich is 20mm or 1/2 inch. Can i continue with 25mm ppr pipe and make 25mm system bathroom? Its not logical to go from lower to higher diameter i know but could it work?
You are grrrreat teacher
Thanks!!
flow will increase with the same diameter output. but not psi. for example if your source only has 100psi using a larger pipe goin to your house wont increase psi. the flow will not also increase unless your output would be same same size in your input. but that's not the case. there will always be a consideration from your source, your pipe will go through valves water meter and at the end faucet which only have the average flow rate that is between 1.0 gpm and 2.2 gpm.
12 years ago i opened the walls in the house replaced all the 1/2" copper with 3/4" copper & foam pipe insulation ($4400 job) because every time the washing machine turned on when im in the shower i'ld get blasted with cold water. 3/4" solved the problem no noticeable pressure change but now it takes about 5 seconds for hot to reach the kitchen faucet it's not immediate anymore dont really care anyway and the bathroom shower/ water heater are opposite ends of the house. question: why does basement hot water pipe freeze and the cold pipe never? why not run pex? because it expands/contracts it's noisy
I've never heard that, both hot and cold water pipes can freeze and I haven't used enough of the rubbery plastic piping to provide you with any relevant information on whether or not it should or should not be used.
So what's your conclusion?
Bigger pipes deliver more water faster.
Pipe use from water supply is 3/4. If i change the pipe to 1" after the meter will it increase the flow of volume?
More than likely, one time I worked on a house where it had a three-quarter inch line coming off of the water meter on both sides and the homeowner installed a 3 inch line that ran for about 300 feet and then stepped back down (three-quarter inch and half inch water supply lines) to feed two houses that had plenty of water pressure.
Following the formula: pressure and volume are inversely related; as one decreases, the other increases.
So as the volume increases flow will decrease but because it's an incompressible liquid pressure will stay the same.
@@bobjoatmon1993 Correct. This is what i was taught.
This is how flow rate is calculated:
Q = A (area) x V (volume)
The greater the area, the greater is the flow, and the greater is the volume of water.
Thanks for sharing.
I have to correct you.
Yeah it's Q = AV
A = area
V = speed... Not volume
You skipped two sizes between 1in and 2in. Commonly 1-1/4 and 1-1/2 are both available.
I didn't include a variety of different sizes in the video, to make the video a little shorter. Keep in mind that the main point of the video is to provide viewers with just how much water flows through pipes with incremental changes in their diameter.
Dude use metric then math don't lie
How does a unit of measurement make a difference?