To read the pump curve would I have to convert the total dnamic head into pressure, if so how can I do it?

Question

To read the pump curve would I have to convert the total dnamic head into pressure, if so how can I do it?

Answer 1

Edited

Pumps marketed to the homeowner are often cataloged showing capacity and pressure. However, centrifugal pump curves are usually presented with the pressure already shown as TDH (total dynamic head) of whatever fluid is being pumped. If the fluid is cold water the conversion is 2.31 ft/psi. So a pump rated at 100 ft TDH for a given water flow would raise the pressure of that water 43.3 psi as it passed through the pump. If the fluid being pumped had a specific gravity different from water the TDH would still be the same, but the developed pressure rise would be different too by the same ratio and so would the horsepower.

In some installations the TDH is divided between the suction lift and the discharge pressure. For instance if that pump was 10 ft above the pond or river, and it could suck the water up 10 feet , the discharge would be 90 ft or 39 psig.

Pumps are limited as to how many feet they can lift water and whether or not they can pump hot water at all. This gets into NPSH (net positive suction head) which is a bit complicated to explain. It involves atmospheric pressure, the temperature and vapor pressure of the fluid, the elevation of the liquid above or below the pump, piping losses in the suction, the dynamic loss in that pump entrance. That entrance loss is sometimes shown on a companion curve showing capacity.

The differences in velocity pressure between the inlet and outlet are insignificant when compared to the total pressure and , except for NPSH considerations , those velocities are generally ignored in engineering applications.

Answer 2

\ P = \rho g h +P_a

*Use hydrostatic law:

P=ρ*g*h + Pa

where,

    * P is the hydrostatic pressure (Pa);

    * ρ is the liquid density (kg/m3);

    * g is gravitational acceleration (m/s2);

    * h is the height of liquid above (m);

    * Pa is the atmospheric pressure (Pa).

*For direct conversion , please click:

http://www.engineeringtoolbox.com/pressu...