Water pipe and pressure

If we are talking about schedule 40 pipe the larger the pipe the less pressure it will handle. You will need to look at pressure ratings for what ever type(steel, PVC, CPVC) you plan to use to see if it will handle the head pressure.

GA!

Hello sb,

Wish I was as clever as you.........Good explanation Sir........GA!

Take care .........................

If you use a bigger pipe with the same flow your pressure will increase. The friction loss decrease with pipe size.

However outlet points or emitters will discharge more water when the pressure increases.

For normal domestic and watering animals you will almost be assured of a higher pressure with the bigger pipe. With the same number of emitters it is impossible to have a lower pressure.

Note the pipe class should be determined by the static height (closed valve situation) and not the reduced pressure due to friction loss.

That is easily taken care of by reducers and taps as well as smaller diameter tapping points at the user end (it is done with the domestic water line isn't it ? the water is usually transported in a few ft dia pipelines.

Hi sb

A lot of people mistakenly take increase of velocity in a smaller pipe as an increases in pressure.

In my youth I was assisting in a column in a farmers periodical regarding technical questions and came across some funny ideas.

One farmer had a siphon over a valley with a smaller pipe on the uphill side. He and his neighbours assured me he gained a few feet that way. He did not trust my theodolite proof as well.

We have a case here on a golf course housing scheme where the pipe class was reduced because they are using PRV'S only to find out that the PRV's do not work on small flows and the pipes are bursting.

you can use the PRVs on smaller flows as long as you have a pressure relief valve. This means some water loss, bu on a gold course this water bypassed by the relief valves can be returned to a watering system and used when they water the grass.

Not in this case (it is a 800ha housing scheme with a golf course)

The cost of the piping to drain the "leaking" water to the nearest common point is more than the original saving on the lighter pipe class.

It is also dolomite area and a leak into the soil will cause a sinkhole.

First of all let us understand the relations beween the capacity of water flowing through the pipe measured in GPM /LPM etc and pressure or head of water column and the diameter of the pipe. If we keep the the pipe diameter as constatnt at 3/4" then with increase in the capaciry there will be higher friction losses which will result in requirement of higher pressure or head of water column for pump to dvelope to deliver the water up 50 fet verticle head. Assuming that flow capacity is constant, pipe size constant with 300' running pipe and 50' vertical head, pump will be required to devlope a pressure head that will be equivalent to 50' of water column(A lbs/Sq Inch) plus the Friction loss head due to the water flowing through 1) 300 feet horizotal pipe( B lbs/Sq Inch)+ 2) 50' verticle pipe ( C lbs/Sq Inch) + 3) Friction losses through the number bends, couplings etc in 350' pipe line( D lbs/Sq Inch)

Since cpapcity of flow will be available in pump performance chart the friction losses can be found out from the friction loss tables generally available with all pump manufacturers. Thus the the total head / pressure required to be developed by the pump will be equivalent to A+B+C+D Lbs/Squ Inch. Since the cpacity and head developed by a pump are limited by the size & the hp of the pump selected, only thing that can be made variable will be the pipe diameter. With increase in delivery head / discharge pressure due friction losses the pipe size has to be increased to minmise the firction losses to deliver whatever capacity of water available through the pump to 50' of water column.

Chitaranjan Nagrecha

Hello digger,

If you increase the pipe diameter, you will increase the flow rate, but decrease the pressure.

You say that you are thinking of running 3/4" pipe - instead of what?

What is your desired flow rate?

You have not given enough information as is so frustratingly prevalent on this site.

Mike

Its 2.5 k.g. pressure

Pertinent is of the number of elbows and T's in the 300' run

What I'm doing is running a 3/4" line gravity feed from a spring to a barn apx. 300 ft with the black water pipe with no bends or 90's to a watering tub and a hose which I would like to have a fair amount of pressure, If going to a larger pipe will give me more pressure that is what I will do, the flow seam to be not a problem, there is a 3/4" pipe already there that we are replacing due to age. we would just like a little more pressure if installing a large pipe would do the trick. The spring is apx. 50 ft above the barn.

Hello digger104:

Not sure if you have been reading the other posts at all? It seems as if you have the idea that a larger dia pipe with give more pressure?...................IT WON'T!!!

If you want a larger capture then use a drain pipe if you want but, reduce it to ½" and you will have brilliant pressure.

You will be wasting your time if you run a larger pipe all the way to your greenhouse. All you will have is a good pond filler.

No offence meant here OK?

Hi digger104

I disagree with babybear

If you replace your gravity pipe with a bigger pipe you will get higher pressure because of the lesser friction losses.

It will however never be higher than the 50ft static.

For using the hose for cleaning purposes a bigger pipe with a smaller nozzle would be the best. The hose should be limited in length because it also reduces pressure due to friction loss.

Ask your pipe supplier for friction curves,

You can determine the maximum percentage volume increase by going horizontally on the curve.

Your maximum pressure increase can be determined by going vertically on the graph.

Your actual duty point will be somewhere between the 2 maximums - that is higher flow and pressure.

Hi digger104

From sb's tables

At 4.8 GPM your pressure at the outlet will increase by about 40%

At equal frictions your flow will increase by about 40%

A rough guess with a 1" gravity line your flow and pressure might increase by 20%.

That is 4.8 to 5.7 GPM and 32.6 to 39.2 ft pressure.

Whatever you do don't go for a 1/2" pipe your flow may drop to 3 GPM and your pressure may drop to 20 ft.

Hello Hendrik,

Hope you are OK?..................With regard to my post I did say he coulc run a drainpipe to the user end. And although I did not make it clear, I meant run 1/2" for the last 6", to allow connections at the spray end to be high.

Can you confirm that would actually give a higher pressyre on the spray?

Take care.....................

I did not read much further than the won't ,

A 1/2" (or smaller) nozzle or short pipe at the end should give him a higher velocity for some tough cleaning jobs.

He would for sure get a better pressure with 1" pipe.

A bigger than 1" pipe will give a better pressure but the gain will now be small and it will not be cost effective.

Keep the 3/4" supply add a manifold and a tank with capacity of water necesary for hose use, plus a bladder to increase pressure.

FROM PRACTICAL EXPERIENCE: I have a similar setup and 3/4" plastic is fine for domestic use. Anything larger than 1" is overkill. One possible problem is air lock, which I remedied by adding a "T" port and access at a hump in the line. Use an oversized strainer at the springbox and keep surface runoff away from your collection area. Freeze up is another problem here in the Catskills of NY.

Good luck, Carl

50 ft of positive head will give 21.65 PSIG of pressure.At a no flow condition, a gauge will read the same at the end of a 300 ft pipe of any size. When flow begins, losses begin., the pressure drops.The more flow, the more loss.The larger the pipe, the less loss per linear foot.A 1 inch pipe will carry 4 times as much water as a 1/2 inch pipe.Your pressure will never exceed 21.65 psig no matter the size of pipe.The velocity, however, can be increased at the end of the line by reducing the diameter of the tap off, such as a nozzle.The pressure will remain the same, however,but it will appear to have more pressure due to the increased velocity. I would go with a 1 inch pipe.It will carry nearly twice as much as a 3/4 pipe.The cost difference is negligible compared to a 3/4 pipe. Good luck. ------------------------------- HTRN-----------------------------------------------I am a kleptomaniac, but when it gets really bad, I take something for it--------

It seems like everybody has been arguing apples vs oranges. Pipe size will not effect static pressure... as stated above it is the same with any size pipe. Pipe size will effect dynamic pressure; entirely based on the volume passing through the pipe.

Hello, If it were me I would run a 1"-1-1/4" pipe. If you use the same size nozzle you will increase the pressure closer to the maximum 50ft head because less friction. But I don't think it will be a very big pressure increase any way you go because 50ft of head is what your pressure is derived from. Personally I would not go any bigger than 1-1/2" though because the increase in pressure will not be great enough to justify the cost of bigger pipe IMO. I also would not run run black pipe for water but rather hot dipped galvanized pipe because it will last allot longer. If you want more pressure look into installing a booster pump with a stand pipe in order to prevent cavitation.