Ross Mackay là một chuyên gia có tiếng trên thế giới về gia tăng độ tin cậy của bơm. Ông là chuyên gia trong việc giúp các công ty gia tăng độ tin cậy của bơm và giảm chi phí vận hành và bảo dưỡng qua các chương trình đào tạo về bơm. Ông là tác giả của cuốn: “Sổ tay thực hành bơm”, và bạn có thể viếng thăm website của ông www.practicalpumping.com.
Ross Mackay is an internationally renowned expert in pumping reliability. He specializes in helping companies increase their pump asset reliability and reduce operating and maintenance costs through pump training programs. He is the author of The Practical Pumping Handbook, and can be reached at 1-800-465-6260 or through his website at www.practicalpumping.com
|| Ross Mackay Associates Ltd.
4 Simmons Cr., Aurora ON
Canada L4G 6B4
| Ross Mackay Associates Ltd.
P.O. Box 670-PMB-29
Lewiston, NY, 14092
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The Pitfalls of Pump Piping
There are three major problems associated with poor pump piping.
1. There is a scarcity of accessible information available on the topic.
2. No one pays any attention to it when installing a pump.
3. It can remain undetected and cause repetitive pump failures for many years.
As a consequence of 1 and 2 above, most pumps are piped up incorrectly. In fact when we look at the way many pumps have been installed, it resembles a “plumbers nightmare.”
Net Positive Suction Head
“Never, in this world of human conflict, have so many been indebted to so few for so much.”
These words were delivered by Winston Churchill when he was Prime Minister of Britain, in praise of the Royal Air Force during the early days of the World War II. Today, they could be easily attributed to NPSH and Cavitation. Engineers all over the world are indebted to a very tiny percentage of the operating family of pumps for an over-abundance of analysis, discussion and confusion.
What The Pump Was Designed to Do
Contrary to popular opinion, a centrifugal pump is not designed to develop one head at a single capacity as requested by the pump purchaser. In fact a pump is designed and produced to supply a whole range of head-capacity conditions as identified on it’s performance curve. The pump will operate on that curve only if it is driven at the particular speed for which the curve is drawn. However, the actual conditions on that curve at which the pump will run, will be determined by the system in which it operates.
Cavitation or Not
Is this really cavitation I am dealing with, or is it air entrainment or recirculation? The reason for that question is that all three conditions have almost identical symptoms. Air entrainment and recirculation will also cause the same rumbling/rattling noise and high vibration as cavitation, as well as the recognizable impeller pitting damage. The major difference is that cavitation is an NPSH problem, while the other conditions have nothing to do with the suction pressure or NPSH.
Some Dangers of Batch Processes
At the end of every batch, the pump was vibrating so badly, it would shear the hold-down bolts and move off the baseplate. The pump in question was used to empty the raw wort (essentially unprocessed beer) from a large tank. The line to the pump suction came from a bottom connection in the tank, through a 90 degree elbow and a short section of line to the suction flange of the pump.
Mechanical Seal Selection Basics
Once referred to as the “black box” inside a pump that no-one really understands, the mechanical seal is that other part of the process pump that is constantly failing. To help alleviate that unworthy accolade we must understand the most important aspects of the mechanical seal.
“One Size Fits All” most definitely does not apply in this area of pumping. Even when we define a Slurry as a mixture of solid particles in a liquid that is usually water, we are still concealing a multitude of applications behind a simple sounding phrase. The variety of solids that are handled in slurry form covers an extraordinary wide range of products and waste material.
Multiple Pump Operations
One of the challenges that face pump users quite frequently, comes into play when more than one pump is required to operate at the same time on the same system. With such multiple pump systems, there are two arrangements where the operating characteristics of the different pumps can be considered to provide a single combined performance curve.
As one of the parts that is manufactured to t
he most exacting of tolerances, the ball bearing does not deserve it’s reputation in the process pump market as being one of the two parts of a pump that is constantly failing. Yet that is the reality. To alleviate this situation, we need some understanding of what bearings do and what we need to do in order to let that happen.
A Practical Approach to Pump Reliability
Over the last 15 years of a 40 year career in pumps, I’ve had the opportunity of training in excess of 20,000 engineers and technicians in pump reliability. This has provided me with the privilege of hearing the problems of that same number of pump users in the same period of time. From this experience I’ve learned 3 things;
1. Most of these problems are very practical.
2. Their solutions are also very practical.
3. Repetitive pump failure can be stopped.
Positive Displacement Pumps
In the many differences that exist between centrifugal and positive displacement pumps, one which has caused some confusion has been the manner in which they each operate within the system. Positive displacement pumps operate with a series of working cycles where each cycle encloses a certain volume of fluid and moves it mechanically through the pump into the system.