8 replies to this topic

[asade abiodun]

Good day,

I had a discussion with a colleague on reading the pump head value from the attached pump curve.

Assume the throughput capacity from the pump is 1,250 gpm. From the curve, the corresponding Total Discharge Head is 164 ft.

My partner said since the TDH axis doesn't start from zero,it starts from 40 ft. Therefore, the corresponding head at 1,250 gpm should be 164 - 40 = 124 ft. My suggestion was that the value should be taken directly.

I would like to know what is the best way to read this TDH on this curve when its axis doesn't start from zero.

Your comment is highly appreciated.

Attached Files

•  Pump Curve.doc   1006KB   110 downloads

Edited by asade abiodun, 13 July 2012 - 03:59 AM.

[pawan]

I am not able to understand how could you read 164 ft at 1250 gpm, it is ~185 ft roughly. (Ankur is right)
Now second part - 40 ft is not to be deducted as this is actually the shut off head for this pump.

Edited by pawan, 13 July 2012 - 04:20 AM.

[ankur2061]

Asade,

I can't read 164 ft from the pump curve. What I am reading is 185 ft corresponding to 1250 gpm from the head-capacity curve.

IMHO, the total differential head value should be directly read as 185 ft and not as 185-40 = 145 ft.

Regards,
Ankur.

[asade abiodun]

Thanks Ankur, I read the value wrongly. You are right.

[ankur2061]

Pawan,

The shut-off head in this pump curve is 218 ft where the head-capacity curve intersects the y-axis (0 gpm flow).

Regards,
Ankur

[kkala]

Some data coming directly from the presented centrifugal pump curves may be also useful.

1. Head at Q=1250 gpm is H=186 ft of liquid, as explained in previous posts.
2. Shut off (if a discharge valve is closed to result in 0 gpm) will create a head of 218 ft, see previous post.
3. Pump efficiency at 1,250 gpm is e = 59%.
4. Brake power at 1,250 gpm is about 102 HP (liquid sg = 1.03).

The latter can be also calculated from rest available data, Q, H, e, sg, since in consistent units brake power = Q*H*ρ*g/e (ρ = density, g = gravity acceleration).

Note: In US customary units brake horsepower = 186*1250*1.03/0.59/3960 = 102.5 HP (Perry, 7th edition, pumping of liquids and gases, p. 10-23, formula 10-51).

But better, if not sure about the formula, to convert units to a consistent system; e.g. H = 56.69 m, Q = 0.07886 m3/s, ρ = 1030 kg/m3, g = 9.81 m/s2, resulting brake power 56.69*0.07886*1030*9.81/0.59 m*m3/s*kg/m3*m/s2 = 76563 Nt*m/s = 76.563 kW = 76.563/0.7457 HP = 102.7 HP.

[asade abiodun]

Thanks kkala

[Shivshankar]

Asade,

Hope this helps

https://app.qleapahe...?asset=85798,63

Regards
Shivshankar

[Steve Hall]

That's a funny looking pump curve; I don't recall seeing one with an inflection in the middle. TDH is usually defined as "Total Dynamic Head" not "Discharge" head. That's because this is the pressure increase imparted by the pump at operating (or "dynamic") conditions. Unless the pressure at the suction nozzle of the pump is exactly 0 psig, a pressure gauge on the pump discharge will not equal the value given by the chart.

My new book discusses how to read pump curves. The complete table of contents as well as spreadsheets that complement the book can be found on my website at www.pipesizingsoftware.com/book. I'm attaching the pages that describe centrifugal pump curves (these are from my original manuscript and do not depict the typeset printed pages in the published volume).

Steve

Attached Files

•  05 - Pumps - selected pages.pdf   618.65KB   111 downloads