Page 113 - Know and Understand Centrifugal Pumps
P. 113
Know and Understand Centrifugal Pumps
Figure 8-2
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Determining the Hs
Of the four elements of the TDH, the Hs and the Hp (elevation and
pressure) exist whether the pump is running or not. The Hf and the Hv
(fiction and velocity losses) can only exist when the pump is running.
This being the case, we can show the Hs and the Hp on the vertical line
of the system curve at 0 gpm flow. The Hs is represented as a T on the
graph below. For example, if the pump has to elevate the liquid 50 feet,
the Hs is seen in Figure 8-2.
Determining the Hp
The Hp also can exist with the pump running or off. We can represent
this value with an 0 or oval on the vertical line of the below graph. The
Hp is added to and stacked on top of the Hs. Let’s say that our system
is pumping cold water and requires 50 ft of elevation change and 10 psi
of pressure change across the system. Now, our pump not only has to
lift the liquid 50 ft, but it must also conquer 23 ft of Hp. Remember
that 10 psi is 23.1 ft of Hp:
10 psi x 2.31
Hp =
SP- gr.
Here is the system curve showing Hs and Hp (Figure 8-3).
