The Cupertino Sanitary District (CSD) recently underwent significant equipment upgrades at its lift stations. The district's submersible pumps now operate with a new type of impeller designed to virtually eliminate blockages. During the year following the pump retrofit program, the utility saved several thousand dollars by preventing all but one blockage. Additional energy savings are being realized due to the suspended high operating efficiency offered by the new pumps.
Products in Action: Pumps
Recommended preventive maintenance checks for centrifugal pumps and drives.
Machinery Reliability Programs
Centrifugal pump fits and clearance checklist: Basic data.
What is L3/D4 (L cubed over D to the fourth)? It is a measure of pump rotor stiffness, its ability to resist radial load and to minimize deflection. It comes from the basic cantilevered beam deflection formula, which you can find in any book on mechanics: y = F x L3 / (3 x E x I), where F is radial load, L is cantilevered length, E modulus is the elasticity of the material and I is moment of inertia.
Why is stainless steel so good against cavitation? If it were soft, wouldn't the imploding bubbles erode the material away in no time?
Is 316ss Soft or Hard?
One of the claimed advantages of centrifugal pumps over positive displacement pumps is their ability to operate over a wide range of flow. Since a centrifugal pump operates at the intersection of a pump curve and a system curve, by varying the system curve the operating point of the pump easily is changed. The convenience and simplicity of such flow control by the discharge valve throttling comes at a price because a pump is forced to run either to the left or right of its best efficiency point (BEP). The flow must be limited on both sides of the BEP.
Suction and NPSH
A "stable" curve is very important for a pump operation, especially for pumps operating in parallel. The higher the energy level and the more critical an installation is, the more this could become an issue.
The following case study describes a reliability problem with a Liquified Petroleum Gas (LPG) handling pump in a field and the way it was troubleshooted and fixed.
A shielded, grease-lubricated ball bearing can be compared to a centrifugal pump having the ball-and-cage assembly as its impeller and the annulus between the stationary shield and the rotating inner race as the eye of the pump. Shielded bearings are not sealed bearings.
Bearings and Lubrication
The following are general pump safety guidelines to keep in mind on the job.