Vertical Turbine Pump TDH Calculation

[jma1970]

Hello all:

Design scenario:
Vertical turbine pump pumping concentrate discharge to a containment area. Existing pumps to be analyzed with a new pipeline extension.

If min water level at turbine intake/tank is 23.5 feet, top of pump is at 31.0 feet and discharge is into containment area at 2.0 feet with no tailwater AND there is a high point in the system, how do you calculate TDH?

A coworker stated that I only take elevation of water level upstream and discharge elevation downstream into consideration (plus friction losses). I have been told in the past that the high point must be considered for what the pump sees for TDH calculations.

Will someone please clarify this for me?

 

[Artisi]

the high point will be considered on start-up as the pump has to achieve this head, this might be left along the performance curve but you have to ensure the pump can reach this head (you haven't stipulated the elevation of the high point, for all we know it might be 100ft). Once flow commences and if a syphon can be maintained then the high point elevation is no longer considered.

Now depends on how the performance curve is presented, if it is a turbine only curve then the head when becomes elevation of the sump level at the operating point or the minimum level to the discharge elevation + column, dicharge elbow etc + friction losses of the pipeline + valves etc. If the curve includes all losses upto the discharge flange then the head is looks like being 2ft + friction losses.

 

[jma1970]

Thanks.

The curve is the turbine pump curve only for the existing pump that is in place now.

The high point is 29.9 feet. The initial question was really relative to theory in as much as you do have to review the high point elevation and not just take the water levels at suction and discharge side of the pump into consideration.

I believe you have stated as such. In this case, the high point is below the discharge elevation of the pump (approximately 32.0 feet) so it can be negated from my understanding here of this particular scenario, correct? (Before reviewing As Builts, we did not have all the existing elevations and the theory was what was being discussed internally).

However, if we did have a point which was higher such as 60 feet, we would add the elevation from suction side water level to pump discharge centerline, then add the elevation to high point, plus friction and minor losses to obtain the TDH, correct? This is assuming that the water is thus pumped up to the highpoint and flows via gravity over the "hump" to the outfall. Am I understanding this correctly?

 

[JJPellin]

I have only one additional comment. If the high point is more than 32 feet above the elevation at the discharge location, then the siphon cannot completely recover the head to the top. Depending on the configuration, you would draw a full vacuum at the top and loose some of this head on the downstream leg.

Johnny Pellin