System curve determination

[nucleareng78]

There is a large diameter vertical pipe with a high flow rate. The flow is going from north to south and we are taking a smaller diameter horizontal line off the side of this pipe. My question: how do I begin to draw a system curve for the inlet of the line we are taking off the large diameter pipe? I know what the NPSH avaliable is based off the elevations but it is slightly confusing to figure out how much resistance is in the system at this point...

Any good resources for developing a system curve? I have an existing hydraulic calculation for the leg of pipe we are looking at but trying to draw the system curve on the vendor supplied pump curve is really tripping me up. I know the minimum design flow/head but no where does it determine the max flow/head. Also, the impeller cannot be trimmed so we can only change the orifice plate at the discharge piping to put more resistance on the system...

 

[BigInch]

The vendor's pump curve shows differential head, so is not directly overlaid onto a system curve, or v/v.

The pump's suction pressure at all points in the range of flow you want to consider (converted to head) is first added to all the corresponding points on the pump curve. Take the combined curve now. Then you can superimpose the heads of the discharge piping system curve directly on the pump&suction curve.

"People will work for you with blood and sweat and tears if they work for what they believe in......" - Simon Sinek

 

[nucleareng78]

Thanks big inch. There is an existing calc that I should be able to use but it doesn not include the orifice plate at the discharge. This would be on the system curve right?

 

[BigInch]

Yes. You've got it. A fixed orifice diameter will have varying heads increasing with flows. Calculate the head loss across the orifice for all flows in your operating flowrate range and add each of those head loss values to all corresponding points on the existing system curve.

"People will work for you with blood and sweat and tears if they work for what they believe in......" - Simon Sinek

 

[nucleareng78]

Orifice plate increases the pressure in the system correct? From my understanding is that it will push the pump operating point back on the curve (flow goes down, pressure go up). SO I would add the additional head generated in the system to each pipe in the system?

 

[BigInch]

Yes, correct.

"People will work for you with blood and sweat and tears if they work for what they believe in......" - Simon Sinek