The hydraulic performance of a slurry pump naturally affects the mechanical load on various parts of the pump design.
For all centrifugal slurry pumps there is only one point which is really ideal for the particular slurry pump involved - the Best efciency point (Bep).
This point is located at the intersection of the best efciency line and the line relating differential head to volumetric ﬂow rate at a particular pump speed.
"Bep - the optimal operating point for the pump!"
Why is this point so important?
Hydraulic effect of efciency point operation
To fully understand the importance of operating at (or close to) the best efciency point we have to study the hydraulic behaviour in the pump.
If we look at the hydraulic effects on the page before we can notice the following effect on the slurry pump design.
Within a centrifugal pump casing there are unbalanced pressures acting on the impeller, causing the pump shaft to deﬂect.
In theory, this radial force applied to the impeller is negligible at the best efciency point (BEP).
At increased speed and ﬂows both above and below BEP, the radial force increases signifcantly.
Pressure distributed on the front and back shrouds of a pump impeller create an axial load towards the pump inlet.
For slurry pumps which are of end suction type, the inlet pressure acting on the shaft cross-sectional area creates an axial load away from the pump inlet.
The summation of these two forces gives a resulting axial loading on the shaft.
With a low inlet pressure (head) this net force acts towards the pump inlet, but with vanes on the back shrouds, this force is normally balanced.
As the inlet head increases, the force acts away from the pump inlet.
Effects of shaft deffection
Varying impeller loads cause the impeller and shaft to deffect. This shaft deﬂection has an adverse effect on the shaft sealing as well as bearing life.
Excessive shaft deﬂection will cause mechanical seals to fail and packed stufng boxes to leak.
As shaft packings not only seal a stufng box, but act as a hydrodynamic bearing, excessive shaft sleeve wear could also occur following operation under high radial load/shaft deﬂection.
Operating at Bep - summary
"Selection of a pump that operates at or very near its BEP is preferable, although not always possible with a limited range of pumps.
At BEP, radial load and shaft deﬂection are at a minimum, thereby ensuring good shaft seal and bearing life.
Power absorbed is at a minimum and smooth hydraulic ﬂow is assured.
For slurry pumps, the minimum of turbulence and recirculation at BEP also equate to minimum wear".
Hebei Tobee Pump Co.,Limited