Centrifugal Pumps are mechanical devices used to transport fluids, typically liquids, from one place to another. These pumps operate by using a rotating impeller to create centrifugal force. This draws fluid into the pump, increases its pressure and propels it out of the pump through the outlet. This mechanism allows for the efficient transfer of liquids in various applications.
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Centrifugal Pumps are widely used in the Industrial and Hygienic industries, catering to Food & Beverage, Pharmaceutical, Water & Wastewater Treatment as well as Paint and Paper applications, and are renowned for their efficient fluid-handling capabilities.
Ensuring correct safety measures are in place and adhered to is essential when working with and operating Centrifugal Pumps. Here are a few of the reasons why these safety measures are necessary:
To mitigate these risks, safety measures such as training for operators, the use of Personal Protective Equipment (PPE), regular inspection and maintenance, proper installation and adherence to safety protocols and guidelines are vital.
Additionally, safety devices and alarms can be installed to control and monitor pump operation. This will help to prevent accidents and protect both personnel and equipment.
1. Equipment Inspection & Maintenance:
Regular inspection and maintenance of your pumps are crucial for safe and efficient operation. Execute a scheduled inspection program to assess components such as impellers, shafts, seals and bearings for damage and wear. Ensure moving parts are correctly lubricated, pump components are aligned and electrical connections, wiring and motor controls are inspected. We recommend keeping a detailed record of inspections, maintenance and repairs. You also have the option to install pressure relief valves or systems to prevent over-pressurisation of the pump and system.
2. Proper Installation & Alignment:
Prior to installation of your Centrifugal Pump, carry out a site assessment to ensure a suitable location is identified. Factors like foundation stability, access for maintenance and proximity to power sources should all be considered. Prepare a level and stable foundation to support the pumps weight and vibrations. During installation, align the pump and motor using alignment tools. You should also pay close attention to torque specifications when tightening bolts and fasteners to prevent loose connections and leaks. If the pump is coupled to a motor, install the coupling correctly and ensure that coupling guards are in place to prevent accidental contact with moving parts.
3. Personnel Training & Certification:
Training should cover pump operation, maintenance, safety protocols and emergency procedures. Certified operators are better equipped to handle pump-related challenges, identify potential issues and respond to emergencies effectively. Proper training enhances overall safety, minimises the risk of accidents and promotes efficient pump operation.
4. Safe Start-Up & Shutdown Procedures:
Establish clear and documented protocols for the safe start-up and shutdown of Centrifugal Pumps. Before starting, ensure that all system components are in proper working order, valves are correctly positioned and personnel are aware of their roles and responsibilities. During shutdown, follow a systematic process to depressurise and secure the system. Proper start-up and shutdown procedures minimise the risk of accidents, protect equipment and contribute to the efficient pump operation while promoting safety in the workplace.
5. Monitoring & Controlling Pump Parameters:
Continuously monitor and control critical pump parameters such as flow rates, pressure levels, temperature and motor conditions. Use appropriate tools and automation systems to ensure that the pump operates within safe operating limits. Install alarms and shutdown mechanisms to respond quickly to deviations. Regularly calibrate and maintain monitoring equipment for accuracy.
6. Handling Hazardous Materials Safely:
It’s critical to prioritise safety when dealing with Centrifugal Pumps that transport hazardous materials. Ensure operators are properly trained to handle these materials. This includes accurate storage, transfer and disposal procedures. To prevent leaks or spills, use suitable PPE and containment measures. Maintain emergency response plans and equipment, such as spill kits and eyewash stations, for swift action in case of accidents. It’s always recommended that operators follow industry standards and regulatory guidelines when it comes to dealing with these substances.
7. Emergency Response & Shutdown Procedures:
Create clear emergency and shutdown plans. Designate trained operators to handle incidents like leaks, equipment malfunctions and fires quickly and safely. Establish swift shutdown procedures to isolate the pump during emergencies, with easily accessible emergency shut-off controls. Regularly review and practice emergency response plans with your team to maintain readiness. Remember, well-executed procedures help minimise damage, protect personnel and prevent further escalation during critical incidents involving Centrifugal Pumps.
8. Replace Old Parts:
Often, worn-out components of Centrifugal Pumps lead to workplace accidents and can even damage the pump itself. Even small parts, such as a bearing or casing wear ring, can cause catastrophic safety issues if they’re worn out. If the pump shaft starts to wobble, it can lead to the pump overheating. To avoid this, check the safety suction lines and pipe plugs frequently. Eventually, sealants wear away and can allow foreign objects into the pump itself. Always replace worn-out parts and components as often as possible.
9. Use a Centrifugal Pump for Intended Use:
There are different types of Centrifugal Pumps, and some are only intended to transport a certain type of material. Operators should never run liquid through a pump not designed to handle it. For example, pumping corrosive or flammable liquids through a pump intended for water or waste can lead to complications. The environment should also be clear of dangerous materials, especially if it’s flammable. Using a pump properly will maintain the levels of cleanliness, pressure, temperature and flow levels needed to keep operations safe.
10. Appropriate System Accessories:
Numerous system accessories can be supplied with the pump to extend its usage. Accessories often have alarms that shut off the system during safety emergencies. Examples of such system accessories include:
Some pump specialists have expressed the belief that process plants are lacking when it comes to applying fundamentals and that chasing after high-tech solutions makes little sense if a plant has not mastered the basics. You can easily check if this notion is true for your plant.
Note: The following dimensional data refer to typical centrifugal refinery pumps and are taken from one of my own books (ISBN -152-7) that was published in ). Use this posted version to test your own knowledge and/or that of other staff members at your site. Resist the urge to look up the actual answers (see “fine print” at the end of the quiz) until you’ve selected your own answers to these 20 questions. Give yourself one point for every correct answer. A passing score should be higher than your shoe size.
1. On a 50 mm shaft, preferred radial ball bearing I.D. (bore) to shaft fits are:
(a) 0.”-0.” interference
(b) 0.”-0.” interference
(c) 0.” loose to 0.” interference
(d) 0.” loose to 0.” interference
2. Using the same 50 mm radial bearing, preferred O.D. to housing fits are:
(a) 0.”-0.” interference
(b) 0.” loose to 0.” interference
(c) 0.”-0.” loose
(d) 0.”-0.” loose
3. Back-to-back mounted 50 mm thrust bearing I.D. to shaft fits are preferably:
(a) 0.”-0.” interference
(b) 0.”-0.” interference
(c) 0.”-0.” loose
(d) 0.” loose to 0.” interference
4. Assuming a 50 mm bearing bore, back-to-back mounted thrust bearing O.D. to housing fits are
preferred at:
(a) 0.” loose to 0.” interference
(b) 0.”-0.” interference
(c) 0.”-0.” loose
(d) 0.”-0.” loose
5. Shaft shoulders at bearing locations must be square with shaft (50 mm) centerlines:
(a) within 0.”
(b) within 0.”
(c) within 0.005
(d) within 0.010”
6. Shaft shoulder height must be equal to the height of the adjacent bearing inner ring.
(True) (False)
7. Sleeve-to-shaft fits are best if kept within:
(a) 0.”-” interference
(b) 0.”-0.” interference
(c) 0.” loose to 0.” interference
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(d) 0.”-0.” loose
8. Keyed impeller-to-shaft fits, on single-stage, overhung pumps, are preferably:
(a) 0.”-0.” interference
(b) 0.”-0.” interference
(c) 0.”-0.” loose
(d) 0.002”-0.005” loose
9. Impeller to shaft fits, on multistage pumps, sometimes require interference fits and must be checked
against the manufacturer’s specifications.
(True) (False)
10. Keys should be located in keyways with:
(a) 0.”-0.” looseness
(b) 0.”-0.” interference
(c) 0.”-0.” interference
(d) 0.” loose to 0.” interference
11. For long-term best results and highest reliability, keys should be hand-fitted.
(True) (False)
12. Looking at the following four possibilities (50 mm shaft), assume:
(a) .002”-.003” interference
(b) .015”-.020” clearance
(c) .003”-.006” clearance
(d) .007”-.012” clearance
(A) Select the correct answer for throat-bushing-to-case fit: (a) (b) (c) (d)
(B) Select the correct answer for throat-bushing-to-shaft fit: (a) (b) (c) (d)
(C) Select two (2) correct answers for throat-bushing-to-shaft fits of inline pumps
(depending on shaft size), where throat bushings may act as intermediate bearings:
(a) (b) (c) (d)
13. Looking at the four possibilities listed in question 12 (above), impeller-wear-ring-to-impeller fit
should be as follows:
(a) (b) (c) (d)
14. Impeller wear rings should be secured by:
(a) dowelling
(b) set screws threaded in the axial direction, partly into the impeller and partly into the wear ring
(c) tack-welded in at least two places
(d) any one of these methods: (a) (b) (c) (d)
15. Clearance between impeller wear ring and case wear ring should be 0.010” to 0.012” plus 0.001” per inch up to a ring diameter of 12 inches. Add 0.” per inch of ring diameter over 12 inches.
(True) (False)
16. Referring to question 15 (above), for pumping temperatures of 500 F and over, it is customary to add 0.010.”
Also, whenever wear ring materials with high galling tendencies, such as stainless steel, are used, 0.005” is
added to the clearance.
(True) (False)
17. Impeller wear rings should be replaced whenever the new clearance reaches which of the following multiples
of original values:
(a) 0.005 inches over original
(b) 1.5 times original value
(c) twice original value
(d) three times original value
18. Metallic case wear rings are not to be bored out larger than which of the following percentages of the original
diameter:
(a) 1%
(b) 2%
(c) 3%
(d) 4%
19. Case wear rings made of Vespel CR are suitable for clearances as low as the following percentages of
the opposing impeller eye or shaft diameter:
(a) 1%
(b) 15%
(c) 3%
(d) 5%
20. The allowable axial float of a set of 50 mm back-to-back mounted angular thrust bearings should ideally be:
(a) negative 0.001” to (max) zero
(b) zero to +0.”
(c) 0.001”-0.003”
(d) 0.010”-0.015”
ANSWERS:
(1) a; (2) c; (3) b; (4) c; (5) b; (6) False; (7) d; (8) c; ( 9) True; (10) c; (11) True;
(12) A/a, B/b, C/c+d ; (13) a ; (14) d ; (15) True; (16) True; ( 17) c; (18) c; (19) d; (20) c
Editor’s Note: Click Here To Download A Full List Of Heinz Bloch’s 24 Books
ABOUT THE AUTHOR
Heinz Bloch’s long professional career included assignments as Exxon Chemical’s Regional Machinery Specialist for the United States. A recognized subject-matter-expert on plant equipment and failure avoidance, he is the author of numerous books and articles, and continues to present at technical conferences around the world. Bloch holds B.S. and M.S. degrees in Mechanical Engineering and is an ASME Life Fellow. These days, he’s based near Houston, TX.
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