Pipe Sizing Charts and Flow Rates

I made a really nice chart in Excel but it turns into a mess when copying it here, so here are smaller charts and their explanations:

Cross Sectional Area (in square inches) - Pipe sizes vs. their cross sectional area. Useful for dividing flow between pipes.
size __area
1/2 = .1963
3/4 = .4418
1.0 = .7854
1.25= 1.227
1.5 = 1.767
2.0 = 3.142

Maximum Gravitational Vertical Flow - This is what we look for when sizing drains or DIY overflows. The flow under the power of gravity reaches a maximum in the same way an object reaches Terminal Velocity as it falls through the air. The gravitational force is countered by the waters viscosity (resistance to flow) and the frictional resistance of the pipe. The viscosity creates a minimum vertical length to acheive the maximum flow. If the vertical pipe length is less than the minimum, the flow rate will be somewhat less than the pipes maximum potential.
size _GPM __GPH
1/2 = 2.50 = 150
3/4 = 5.63 = 337.5
1.0 = 10.0 = 600
1.25=15.6 = 937.5
1.5 = 22.5 = 1350
2.0 = 40.0 = 2400

Min. Vertical Length
1/2 = 2"
3/4 = 5"
1.0 = 9"
1.25= 14"
1.5 = 20"
2.0 = 36"

Frictional Head Loss per 90 (measured in Feet of Head)
size_ head loss
1/2 = .00970
3/4 = .00220
1.0 = .00386
1.25= .00602
1.5 = .00878
2.0 = .00156

Anyway... Each measurement is at the pipes maximum flow rate in the Vertical Flow Rate chart. When calculating the loss for the pump side, these values are slightly more.

There is a very conservative rule when estimating head loss. It is one foot of head per fitting. This rule does not take into account flow rates, pressure, actual frictional losses, etc. It does not have to because it is too conservative. If you multiply any of the above head losses by one thousand fittings, you will be very surprised at the actual head loss. (hint: just move the decimal to the right three places.)



Gravitational Horizontal Flow This is for horizontal applications that do not rely on a pump, or the force of a vertical pipe. These flow rates are considerably less than the vertical rates because gravity does not offer a significant horizontal force. It is a balance of gravity and the viscosity vs. the cross sectional area of the pipe.
size_ GPM
1/2 = 1.563
3/4 = 3.517
1.0 = 6.253
1.25= 9.769
1.5 = 14.07
2.0 = 25.0

In this application, you would use the chart for Vertical Flow.







In this application, you would use the chart for Horizontal Flow.

CHOMPERS;2641846; said:

Frictional Head Loss per 90 (measured in Feet of Head)
size_ head loss
1/2 = .00970
3/4 = .00220
1.0 = .00386
1.25= .00602
1.5 = .00878
2.0 = .00156

Click to expand...

I'm still editting, but the timer hit zero

Anyway... Each measurement is at the pipes maximum flow rate in the Vertical Flow Rate chart. When calculating the loss for the pump side, these values are slightly more.

There is a very conservative rule when estimating head loss. It is one foot of head per fitting. This rule does not take into account flow rates, pressure, actual frictional losses, etc. It does not have to because it is too conservative. If you multiply any of the above head losses by one thousand fittings, you will be very surprised at the actual head loss. (hint: just move the decimal to the right three places.)

Jgray152;2647973; said:

Is there a difference in head lose when water is flowing with gravity @ 600 GPH compared to being pumped @ 600 GPH? Because those numbers are very low compared to everything I have seen.

Click to expand...

That is a very good question. Yes there is a difference at different flow rates. The friction is variable and nonlinear for different flow rates and pipe sizes. When I had been looking around, I found that there was a huge discrepency from table to table. None explained the math and it was always "one size fits all" information (no flow rates). That is why there was so much discrepency with the tables. I found a calculator that had the friction coefficient chart as one of the input variables. This is where I got my data. The other important variable was the flow rate. I used the "max gravitational flow rate" for each pipe size in the calculator because that is what most applies to us. The result at this flow rate was always zero (the calculator only returned whole numbers). I had to enter one thousand fittings to get a non-zero result. Since it was a calculator, I could not verify the math but the input data was the most comprehensive that I had found.

As for the part of your question about 600 and 600:
There will be no difference. If the flow rate is the same, the pipe fitting won't know if it is gravity fed or pump fed. If the end were restricted for the pump's plumbing and the flow rate were the same the internal pressure won't really play a part because water is noncompressible (relatively speaking).

The closest table that I found (pumped velocities) were approximately at a ten fold difference. In other words, you would need on the magnitude of 100 fittings rather than 1000 to start to worry about head loss. Even still, we don't use anywere near that many fittings on our tanks.

johnptc;2649659; said:

...above this flow region the flow becomes turbulent and the water molecules no longer flow parallel to the ripe walls........ eg they might swirl around a discontinuity caused by a fitting......in this region frictional forces may be dramatic

Click to expand...

Yes, I have seen that. In extreme cases, there is around a 30% usable size reduction from the eddies and pipe erossion frequently can occur.