Calculate Gauge Pressure On Suction Side of Pump

[cuels]

I am trying to determine the correct method for calculating the gauge pressure on a pressure transducer that will be installed on the suction side of a pump. This transducer will be used to set the water level in a tank that will be feeding the pump. There are several lines entering into the suction header of the pump, so I will have some friction and minor losses. I am trying to wrap my head around how to calculate what the pressure will be when the pump is running. I can easily calculate the static head (~20 feet). The suction losses at the design flow will be about 10 feet. I can easily determine what the gauge pressure will be when the pump is not running, but I can't figure out how to calculate the effect that the running pump will have on the pressure in the suction header. I know it shouldn't be too complicated to determine, but I can't seem to find any information in my textbooks that will guide me in the right direction.

 

[1gibson]

Calculate velocity head

 

[Latexman]

For me, the best starting point is a detailed, close-to-scale, hand sketch on graph or scaled paper. From there, everything seems to come together.

Good luck,
Latexman

Technically, the glass is always full - 1/2 air and 1/2 water.

 

[cuels]

So, in thinking more about it, my gauge pressure should be static head + velocity head - pipe friction loss - minor loss, if that is all I have in the system before the gauge. Does this sound correct?

 

[bimr]

Use the Darcy method:

http://www.engineeringtoolbox.com/darcy-weisbach-equation-d_646.html

or the Equivalent Pipe Length Method:

http://www.engineeringtoolbox.com/equivalent-pipe-length-method-d_804.html

to calculate the pressure loss in the pipe.

The pressure setting for the transducer will be field set so you do not have to calculate a precise number. You should be able to either set the pressure in the field on the instrument, or set the pressure within the SCADA control system.

 

[Latexman]

Most pressure gauges don't read the velocity head: only pitot tubes. Everything else is correct though. Should be static head - pipe friction loss - minor loss (fittings).

Good luck,
Latexman

Technically, the glass is always full - 1/2 air and 1/2 water.

 

[cuels]

Thanks Latexman....that was all I needed!

 

[LittleInch]

I know this isn't the question you asked, but I'm intrigued as to how this will operate. Your phase " This transducer will be used to set the water level in a tank that will be feeding the pump. There are several lines entering into the suction header of the pump" seems to indicate that the pump inlet has multiple lines, from other sources? Therefore I find it difficult to imagine how monitoring the inlet pressure is going to be directly applicable to tank level. Even if it did, the flow will need to be constant to get your fixed friction losses, unless these are minor compared to the head level. how will the control system react when the pump is stopped or starting / stopping?

It all seems an odd way to control a tank level to any degree of accuracy?

a sketch would be good.


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