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Pressure Vs Flow

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• #275494
Webmaster Imos

My question is can anyone tell me by reducing pressure through a pipe, can the volume of water be maintained

• #292252
Harold Kestenholz
Participant

Flow is a result of the force of liquid against the resistance of the pipe. If the pipe after the reducing valve is increased in diameter to accomodate the flow rate of the higher pressure liquid through lowering the total resistance, the flow might approach the flow rate in the smaller input line less the resistance of the reducing valve.

If the resistance of the initial line is reduced through partial substitution of larger pipe, the flow may equal to or may increase with the same liquid moving force. The effect is also dependent upon whether the incoming liquid flow rate is fixed or might increase due to a lowered total resistance.

• #292253
SylvanLMP
Participant

In reply to message posted by neil:
My question is can anyone tell me by reducing pressure through a pipe, can the volume of water be maintained

NO……….

If you want to know more read below or forget it as I gave you your answer.

To get slightly technical

Lets talk basic plumbing.

For example lets think like a 3rd year apprentice and figure it out mathematically.

Lets keep it simple and use a 3″ pipe and lets not take friction losses or other factors in consideration.

Now we take two pressures

50 PSI would give a velocity of 24.59 FPS

100 PSI would give a velocity of 34.78 FPS So far so good huh?

Now we would convert FPS to GPM and we would find the following

A 3″ pipe with a pressure of 50 # would have a flow rate of 24.59 FPS converted to GPM would thus be hovering around 553.27 GPM (sorry I do not have my old apprentice books available so I must do it from memory so please forgive me for not being exact)

Now we take 100 PSI going to a 3″ pipe and we find a flow rate in FPS of 34.78 WHICH in GPM would be 782.55 GPM

I am sure WALLFRAUD would be more then happy to explain how to derive at this and while Fraud is at it he can explain the beauty of using pneumatic controllers slave and master in calibrating a high pressure step down steam system as he be a Heatinnn guy.

When increasing pressure you are increasing the velocity and if your not careful you can cause premature piping failures with erosion and hydraulic shock highly possible.

Hey its a good thing I went to school that day

Got to love how lucky some folks are in P&H as they dont have to ever think about this stuff.

• #292254
Harold Kestenholz
Participant

EXACTLY. As Sylvan indicates, if the pressure IN a pipe that is the same size throughout is reduced (the only way of doing that is to make a blockage) the flow will be REDUCED.

Conversely, if the resistance from one end of the piping system to the other is reduced, while subject to a pressure approximately the same from end to end, the flow can be increased; but only if a long section of the pipe is increased in size to create a reduced total resistance.

The variable is based upon whether the pipe is considered the same only if a section of pipe remains unchanged, or the piping is considered the same after a section of the piping is enlarged.

• #292255
Harold Kestenholz
Participant

However, to continue the postulation: If the flow rate through a pipe is governed by a restriction at the outlet end of the pipe, removing the restriction can make the flow increase in the pipe even though the pressure drops. This variable is based on where the restriction that governs flow is located. This effect can be seen when the pressure drops as a tap is opened to increase flow.

Thus bumblebees can fly.

• #292256
SylvanLMP
Participant

In reply to message posted by Harold Kestenholz:
However, to continue the postulation: If the flow rate through a pipe is governed by a restriction at the outlet end of the pipe, removing the restriction can make the flow increase in the pipe even though the pressure drops. This variable is based on where the restriction that governs flow is located. This effect can be seen when the pressure drops as a tap is opened to increase flow.

Thus bumblebees can fly.

Exactly Grass hopper

BUT

Depending on the flow rate required and the available pressure as you cannot supply a 8″ water main with a 2 ” pipe even with a lot of pressure if the 8″ pipe is fully open.

YOU CANNOT compress water so thus you can only get a certain amount of volume in a given sized pipe.

Think about a pump sucking air from a water main Where does this air come from if indeed the pipe s full of water?

Friction losses and head loss (.434) plus the “Force” if taken into consideration would confuse the Frauds in P&H

Here let me give you an example ask an off the Wallfraud to explain the following.

Say you have a pipe 110 ft high and its 8″ diameter ask these P&H non trainables what is the hydrostatic “pressure” at the base ?

Then ask what is the “force” and see what answers you get on a list that is supposed to have “professionals” on here giving basic answers to simple plumbing questions.

The origional question was very valid and a great topic for helpers to learn that rweal plumbing is not a hit and miss application.

The folks dabbling in these fields without a formal education from a real trade schools are just handymen getting over on the public.

A jetter giving 3,000 PSI through a 3/4″ inch hose will also give me 3,000 PSI through an 1/8th inch hose But if I should increase the orifice size of the nozzles my pressure MAY drop but I know my volume would increase.

Pressure drop is not a given on all systems.

As a Master plumber and a Master Fire Suppression piping contractor (NFPA RULES) WE hydrostatically design our systems to keep flow losses to a minimum with the velocity to remain in safe limits.

“Plumbing” one has to know about sanitary,storm and water piping velocities as all of these are different.

Could you imagine taking a P&H guy and asking them to tell you the speed of STEAM for example flying in a vacuum system.

Ask the average P&H bum to tell you how a boiler on a roof 33 Stories works to supply heat to the entire building STEAM ot hydronics or a combination there of.

Harold these so called trades can get as complicated as anyone wants them if they are willing to ask the right questions rather then knocking someone for knowing something.

Every single day I learn something new like the new systems used for fire supression systems or steam operated elevators which I recently saw.

Harold thank you again for one heck of a web site you have created, this site should atleast make the average home owner much more aware of options in design then some of the unemployables out there unlicensed heating folks are dabbling in.

Thank you Harold for a most enjoyable discussion.

Im still learning so please be patient with me.

• #292257
Harold Kestenholz
Participant

SylvanLMP wrote: Depending on the flow rate required and the available pressure as you cannot supply a 8″ water main with a 2 ” pipe even with a lot of pressure if the 8″ pipe is fully open.

EXACTLY, the original premise didn’t state a requirement that the pipe be fully open. The pipe COULD be partially open. When designing a system, all the parameters have to be clear before you start.

SylvanLMP wrote: The origional question was very valid and a great topic for helpers to learn that rweal plumbing is not a hit and miss application.

Yes, the question contains too little information to come to a single answer, so the experienced would recognize the open-endedness and seek more information if trying to solve a real-world problem.

SylvanLMP wrote: Harold thank you again for one heck of a web site you have created, this site should atleast make the average home owner much more aware of options in design

Thank you, Sylvan; some frauds object to giving knowledge to homeowners, but many homeowners now put low water cutoffs on their boilers and require their repairmen to carry combustion test instruments for economy and safety. This makes more work for skilled plumbers and improves the respect for the skilled Masters in the trades. A skilled tradesman never needs to worry about getting enough good work and certainly doesn’t have to keep others from learning. If they want to stop customers from knowing good service, they should attack magazines and the manufacturers that advertise. The customers that ask questions on this site are never prevented from learning as we all are.

• #292258
SylvanLMP
Participant

“Thank you, Sylvan; some frauds object to giving knowledge to homeowners, but many homeowners now put low water cutoffs on their boilers and require their repairmen to carry combustion test instruments for economy and safety. This makes more work for skilled plumbers and improves the respect for the skilled Masters in the trades. A skilled tradesman never needs to worry about getting enough good work and certainly doesn’t have to keep others from learning. If they want to stop customers from knowing good service, they should attack magazines and the manufacturers that advertise. The customers that ask questions on this site are never prevented from learning as we all are.”

I think more and more home owners should look to sites like yours so they can Quiz the so called hewating guys on what they really know.

Personally I have always felt a LWCO with manual reset should be installed on EVERY SINGLE H/W boiler regardless of BTU input even the peanut sized ones (200,000 or less)

I like high pressure limits MANUAL reset also installed of hydronic boilers.

A lot of Frauds think of operating controllers as safety devices.
Ah the joys of being ingnorant that is why I feel the home owners are much better suited writing the specificcations rather then taking a NON formally trained heatin guy into their home

Give simple basic tests like asking about stay bolts mud legs wheatstone bridges and what is required for an internal and external boiler inspeection.

Harold keep up the fantastic job your doing to educate EVERYONE who really wants to learn.

My best accounts are Briliant folks willing to learn and ask questions.