Engineers- calculate water pressure?

[Fritzo]

Isn't there a formula to calculate water pressure flowing out of a pipe? Something about density of the water and the size width of the pipe? I'm having a product design argument and I can picture the physics in my head, but I can't prove it.

 

[gorcorps]

Static pressure is easy, but you're talking about dynamic flow

http://en.wikipedia.org/wiki/Bernoulli's_principle

good luck

 

[coxmaster]

You're going to need to know the velocity of the water coming out as well as some more information..

 

[Fritzo]

You're going to need to know the velocity of the water coming out as well as some more information..

I have 60PSI pressure on a 1/2" pipe. If you reduce that to 1/32", would the water pressure increase 16x?

 

[SKORPI0]

Measure Your Water Pressure

High Water Pressure and How It Makes a Difference

Why not attach a meter at the end of the pipe (if possible)?.

or this ...... Note - flow and pressure are different.

http://www.professionalequipment.co...meter-995-01sku397-654/water-pressure-gauges/

This Water Pressure Gauge and Water Flow Rate Meter is a useful, comprehensive combination gauge that fits any standard hose bib. A 3/4" brass gate valve controls the water pressure and the water flow. For extra protection of your gauge during storage and transport, you can purchase a cordura case with a shoulder strap and belt loop.

 

[kevinsbane]

I have 60PSI pressure on a 1/2" pipe. If you reduce that to 1/32", would the water pressure increase 16x?

No. It goes up by more than that. 256 times increase in pressure for constant flow.

And not only that, a 1/2" pipe going to a 1/32" pipe (that's tiny!), surface conditions will begin to have an increasing, non-negligible effect and can no longer to be ignored.

 

[Fritzo]

Measure Your Water Pressure

[url="http://www.single-family-home-remodeling.com/high-water-pressure.html]High Water Pressure and How It Makes a Difference[/url]

Why not attach a meter at the end of the pipe (if possible)?.

Because it's not for that

We're talking about a Waterpik gadget we saw today that attaches to your shower head. It's battery powered...and I say that it didn't need to be battery powered. The water pressure could have powered it.

Some are saying it's not strong enough, and I say that standard water pressure through a tiny opening will be insanely strong.

 

[gorcorps]

I have 60PSI pressure on a 1/2" pipe. If you reduce that to 1/32", would the water pressure increase 16x?

Are you sure you're asking the right question? If you know for a fact you're applying 60psi on one end and you're merely reducing, then your pressure will not change... your flow rate would (IIRC)

So are you asking if the flow rate would change?

 

[kevinsbane]

Because it's not for that

We're talking about a Waterpik gadget we saw today that attaches to your shower head. It's battery powered...and I say that it didn't need to be battery powered. The water pressure could have powered it.

Some are saying it's not strong enough, and I say that standard water pressure through a tiny opening will be insanely strong.

For that...

approximate flow through 1/2" pipe at 60psi: 40.78 gpm.

40.78 GPM = 2.5 L/s
At constant pressure, you lose 256x flow rate = 2.5L/s/256 = ~1ml/s. That's under ideal conditions; real flow rates will be somewhat less. 1mL/s isn't much for a WaterPik...

1mL/s = flow speed of 0.5m/s with a 2mm squared hole, or about 1.6ft/s.

 

[edro]

There is an amazing phenomenon known as "pressure drop".
When you step from one diameter to a lower diameter, there is a pressure drop.
Velocity will increase out of the small side, but flow through the larger sized pipe is reduced, thus reducing your outlet flow rate.

The garden hose analogy is common.
Put your thumb over the end of the hose, pressure increases on the hose side.
Flow is greatly reduced, but the velocity out of the hose is increased.
Keep covering the end more and the pressure increase is very high on hose side and flow rate past thumb is so low that even a high velocity cannot sustain the spray.

 

[phucheneh]

Are you sure you're asking the right question? If you know for a fact you're applying 60psi on one end and you're merely reducing, then your pressure will not change... your flow rate would (IIRC)

So are you asking if the flow rate would change?

This. Is your 60psi at the inlet or the outlet? If you're talking about household water pressure, if it's 60psi at the main, AFAIK you will never get higher than 60psi, right?

Fluid through an empty pipe would accelerate faster through a smaller one, but the resulting pressure of a filled pipe is still 60psi. Velocity is not head pressure. And if the flow at said pressure is not adequate, the smaller pipe will produce less while in use.

(Right? I think that's right...)

 

[coxmaster]

Because it's not for that

We're talking about a Waterpik gadget we saw today that attaches to your shower head. It's battery powered...and I say that it didn't need to be battery powered. The water pressure could have powered it.

Some are saying it's not strong enough, and I say that standard water pressure through a tiny opening will be insanely strong.

Sounds like you are more concerned with velocity than pressure...

 

[phucheneh]

Are you trying to spin a little turbine with the water or something? That would be pretty clever.

 

[Hacp]

Are you sure you're asking the right question? If you know for a fact you're applying 60psi on one end and you're merely reducing, then your pressure will not change... your flow rate would (IIRC)

So are you asking if the flow rate would change?

Pressure could change depending on things like fouling, pipe length, bends, etc.

 

[Imp]

I figured this out and kicked the exam's ass in second year college... That was a long effing time ago and I haven't used it since.

 

[Matthiasa]

No. It goes up by more than that. 256 times increase in pressure for constant flow.

And not only that, a 1/2" pipe going to a 1/32" pipe (that's tiny!), surface conditions will begin to have an increasing, non-negligible effect and can no longer to be ignored.

Isn't that what computational fluid dynamics is for?

Or the op could do it the easy way and get a gauge as mentioned.

 

[5to1baby1in5]

There are emperical formulas and tables for measuring the pressure drop per 100 feet of pipe. Flow rate (velocity), smoothness of the pipe, density, viscosity, and others (?) all affect the calculated press drop per 100ft of pipe. You can also determine the equivalent length of pipe for various fittings. A 90 degree bend is equivalent to XX ft of pipe, so you add up all the fittings and straight pipe and calculate the total pressure drop. There is a book called Crane that detailss all of this. They issue it to Proces/Chemical Engineers.

The pressure drop per 100 ft increases as the pipe diameter decreases because the velocity increases (it must because the fluid is incompressable). Also, as velocity increases, kinetic energy increases. Due to conservation of energy, when kinetic energy increases, potential energy (pressure) decreases. These both cause the pressure to drop when the diameter decreases.

 

[5to1baby1in5]

Because it's not for that

We're talking about a Waterpik gadget we saw today that attaches to your shower head. It's battery powered...and I say that it didn't need to be battery powered. The water pressure could have powered it.

Some are saying it's not strong enough, and I say that standard water pressure through a tiny opening will be insanely strong.

Because the flow is low, youtake most of the pressure drop through the nozzle (tip of the waterpik) this increasesthe water's velocity. What blasts the plaque off your teeth is the velocity of the water. Its pressure is 0 psi as soon as it exitsthe tip of the pik.

60 psi of pressure drop may not be enough to increase the velocity of the water to blast the teeth. Can you waterpik your teeth with a garden hose nozzle? 100 psi may be just right. 600 psi would cut your gums.

 

[kevinsbane]

Isn't that what computational fluid dynamics is for?

Or the op could do it the easy way and get a gauge as mentioned.

Yep. I ran through a few of the rough calcs above I'd rather not go too much into it, imperial makes me want to pull my hair out

Besides, computational fluid dynamics requires either assumptions (such as no surface effects) or compute clusters.

 

[iGas]

Simple flow chart for cold water.
http://constructionmanuals.tpub.com/14259/css/14259_50.htm

Pipe Sizing.
http://people.rit.edu/megite/460_pipe_sizing_ASHRAE.pdf

 

[iGas]

Static pressure is easy, but you're talking about dynamic flow

http://en.wikipedia.org/wiki/Bernoulli's_principle

good luck

I think the OP have 60 PSI static pressure, because 60 PSI dynamic pressure would surely blown off all of the fixtures and faucets in the OP house.