Pump shut off head

[nicwong7]

Hello all,

If lets say my tank is 12m tall, my pump rated 7bar, shut off is at 9.1 bar.

While not considering water column/density, where 1bar = 10m, my discharge pressure instruments can be designed as

min Pressure - 0
Normal Pressure - 7+1.2 = 8.2
Max - 9.1+1.2 = 10.3

Is this correct?

Thanks.

 

[LittleInch]

From your data, yes, but it's much better to use the correct wording.

Your pump (centrifugal I assume), generates head across it (Total differential head). This is fixed regardless of density, hence developed pressure is variable depending on density.

Your tank might be 12m high, but where is the liquid?

If at the top then Ok, you have 12m head.

Is it open to atmosphere - If yes then Ok you still have 12m head, but if it's pressurized or below atmospheric pressure, it's a different amount.

Unless you pump is mounted directly on the tank, you will have fluid losses before the pump, assuming you pump centerline is at zero metres relative to your tank height. These aren't listed.

Assuming therefore that your TDH is normally 70m and your shut off head is 91m, your true inlet head is actually 12m

running head is 12 + 70 = 82m

Static head is 12 + 91 = 103m.

If your SG is 1.0, then pressure = m x 100 / 9.81 in bar.

Note that in this case there are no friction losses. In your case there might be only a very small difference, but in many cases this can make the shutoff pressure much more.

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

 

[bimr]

Your pressure calculations are in the range.

Pressure instruments should be designed to read in the middle of the scale, not at the end of scale.