Centrifugal Pump Maintenance Manual: Seal Replacement, Impeller Inspection, and Performance Curve Testing

1. Scope and purpose

This maintenance manual is designed for engineers and technicians who perform scheduled and unscheduled maintenance on standard industrial centrifugal pumps. It covers critical procedures such as replacement of the face seal, detailed inspection of the impeller and casing, and functional testing of the pump by measuring its performance curve. The goal is to ensure maximum reliability, efficiency and service life extension of pumping equipment operated at production enterprises of Ukraine. The application of this guide allows you to quickly respond to malfunctions and implement proactive measures to prevent failures in accordance with the requirements of DSTU EN ISO 9905:2018.

Maintenance should be carried out in cases of: planned maintenance according to the schedule, detection of leaks from the end seal, reduction in pump performance, increased vibration or noise, as well as during major equipment repairs.

2. Safety measures

MUST COMPLY!

Before starting any maintenance work on the pump, ensure that all equipment is de-energized and isolated from power sources in accordance with the LOTO (Lockout/Tagout) procedure. This includes electrical power to the motor, pressurized fluid supply (shutdown of inlet and outlet valves) and any auxiliary power (pneumatic, hydraulic).

• Isolation from energy sources: Turn off the pump and its drive. Lock and tag all switches and valves.
• Relief of pressure: Drain the working fluid from the pump body and pipelines. Make sure the internal pressure is equal to atmospheric pressure.
• High temperature: Allow the pump to cool to a safe temperature if it has been working with hot liquids. Surfaces may remain hot for a long time.
• Chemical hazard: When working with aggressive, toxic or flammable liquids, use appropriate personal protective equipment (PPE) and ensure adequate ventilation. Drain liquids into specially designated containers.
• Rotating parts: Never work on the pump if it is energized and there is a risk of unauthorized starting.
• Heavy components: Use lifting mechanisms to safely move heavy pump parts (motor, casing).

Personal protective equipment (PPE):

• Safety glasses or a face shield: Mandatory for any work.
• Protective gloves: Resistant to chemicals when working with liquids, or durable for mechanical work.
• Safety shoes: With metal toe.
• Protective clothing: Overalls.
• Hear protection: When working near noisy equipment.

3. Necessary tools and materials

4. Checklist before maintenance

5. Step-by-step procedure

5.1. Preparation and dismantling of the pump

1. Perform the LOTO (Lockout/Tagout) procedure:

   Make sure the pump is completely de-energized and isolated from all power sources.

   • Turn off electrical power to the pump motor and install interlocks and warning signs.
   • Close the inlet and outlet valves on the pipelines that supply and remove liquid from the pump. Block them.
   • Open the drain valves and completely drain the working fluid from the pump housing and piping. Make sure there is no residual pressure.
   • If the pump has been operated with hot liquids, allow it to cool below 40°C.

   Common Mistakes: Insufficient fluid flow can lead to dangerous spills and burns.

2. Uncoupling the clutch:
   • Remove the protective cover of the clutch.
   • Mark the relative position of the coupling halves (for example, with a corner or marker) to facilitate reassembly and maintain balance.
   • Loosen the bolts connecting the half couplings. Carefully separate them, making sure that the motor shaft and the pump shaft turn freely.
3. Dismantling the engine (if necessary):
   • Disconnect the electric cables of the engine (take a picture of the connection diagram beforehand).
   • Loosen the motor mounting bolts to the pump frame.
   • Using the lifting mechanism, carefully remove the engine and put it in a safe place.

   Common Mistakes: Incorrectly marking wires can lead to connection errors and damage to the motor.

4. Removing the bearing housing and end seal:
   • Loosen the bolts securing the bearing housing to the pump light or rear cover.
   • Carefully remove the bearing housing together with the pump shaft and the old end seal. Avoid damaging the shaft.
   • Clean all surfaces from the remains of gaskets and sealant.
5. Dismantling the impeller:
   • Fix the pump shaft in a vise with soft pads.
   • Unscrew the lock nut of the impeller (it usually has a left-hand thread, check with the manufacturer's documentation).
   • Using a puller, carefully remove the impeller from the shaft. Never hit the impeller with a hammer, it may damage or unbalance it.
   • Remove the key.

5.2. Inspection of components

6. Impeller Inspection:
   • Perform a thorough visual inspection for signs of cavitation (sponge-like surface), erosion (metal wear), corrosion, cracks, or mechanical damage.
   • Check the edges of the blades for sharpness and the absence of serrations.
   • Measure the outer diameter of the impeller and compare with the nominal value or the minimum allowable.
   • Measure the axial and radial clearance of the impeller relative to the housing or wear rings (if applicable). The permissible radial gap between the working wheel and the wear ring is 0.25 - 0.50 mm.
   • Check the balancing holes (if any) for blockages.

   Common Mistakes: Ignoring minor damage can lead to reduced efficiency and increased vibration.

7. Inspection of pump housing and wear rings:
   • Inspect the inside surface of the housing for erosion, corrosion or cavitation, especially in the area of the cut-off and spiral passage.
   • If the pump has wear rings, inspect them for wear and damage. Excessive clearance between the impeller and wear rings leads to a significant loss of efficiency.
   • Inspect the sealing surfaces of the flanges for deformation and damage.
8. Inspection of the pump shaft:
   • Inspect the shaft for corrosion, cracks, pitting or wear, especially in the area where the end seal and bearings are installed.
   • Using a clock-type indicator, measure the runout of the shaft. The maximum permissible radial runout of the shaft in the sealing zone should not exceed 0.05 mm.
   • Check the keyway for wear.
9. Bearing Inspection:
   • Visually inspect the bearings for signs of overheating, grease fading, cracks, or other damage.
   • Carefully rotate the bearings, listening for unusual noises or roughness.
   • Check the cleanliness of the bearing assembly.
   • If the bearings show signs of wear, they should be replaced. Use the bearings recommended by the manufacturer (for example, class C3 for most pumps).

5.3. Replacement of the end seal

10. Preparation for installation of a new seal:
    • Thoroughly clean the pump shaft and seats of any dirt, rust or remnants of the old seal. Use brake cleaner or other specialized degreaser.
    • Check the shaft for sharp edges or burrs that could damage the sealing elements of the new end seal. If necessary, carefully clean with a fine abrasive.
    • Apply a thin layer of antifriction coating or clean lubricant (compatible with the operating fluid) to the shaft where it contacts the rubber end seal elements to facilitate installation and prevent damage.

    Common Mistakes: Dirt or damage to the shaft is the main cause of rapid failure of a new seal.

11. Installing the stationary part of the end seal:
    • Carefully install the stationary ring (usually ceramic or silicon carbide) into the pump body or cover. Do not touch the work surface with your hands, use clean gloves.
    • Make sure that the stationary ring fits tightly in its seat, without distortion.
12. To install the rotating part of the end seal:
    • Wrap the end of the shaft with clean electrical tape (or use a special mounting cone) so that the rubber elements of the seal are not damaged by the keyway or sharp edges.
    • Carefully push the rotating part of the end seal onto the shaft as far as it will go.
    • Remove the insulating tape/mounting cone.
13. Adjusting the end seal (if required):
    • Some types of end seals require precise axial positioning or pre-compression adjustment. Follow the manufacturer's instructions.
    • Typically, for cartridge end seals, distance setting is automatic, using temporary retainers that are removed after pump installation.

5.4. Assembling the pump

14. Installing the impeller:
    • Install the key in the keyway of the shaft.
    • Push the impeller onto the shaft as far as it will go.
    • Закрутіть контргайку робочого колеса. Затягніть її динамометричним ключем до моменту 80-100 Нм (або згідно рекомендацій виробника). Перевірте, чи робоче колесо вільно обертається, не зачіпаючи корпус.

    Common mistakes: Insufficient tightening torque can lead to weakening of the impeller, and excessive torque can lead to deformation.

15. Bearing Housing and Back Cover Assembly:
    • Install new gaskets or O-rings.
    • Carefully fit the bearing housing together with the shaft and impeller into place, aligning them with the pump housing.
    • Tighten the mounting bolts evenly and crosswise to a torque of 40-50 Nm (depending on the size of the bolts).
    • Make sure that the shaft rotates freely without jamming.
16. Installing the engine and clutch:
    • Install the engine in place and secure it with the bolts, tightening them to a torque of 50-70 Nm.
    • Connect the coupling halves using the marks made during disassembly. Tighten the coupling bolts with a torque of 25-30 Nm.
    • Mandatory Shaft Alignment: Accurately align the motor and pump shafts using a laser alignment system or clock-type indicator. Permissible misalignment: radial - no more than 0.05 mm, angular - no more than 0.05 mm/100 mm of the coupling length.
    • Install the protective cover of the coupling.

    Common mistakes: Poor shaft alignment is the main cause of increased vibration, wear of bearings and end seals.

5.5. Performance curve testing

This procedure is performed to confirm that the pump is operating according to the manufacturer's stated specifications after service.

17. Preparation for testing:
    • Make sure the pump is fully assembled, the piping is connected and the system is filled with working fluid.
    • Install calibrated pressure gauges on the inlet and outlet lines of the pump.
    • Connect a calibrated flow meter on the outlet line.
    • Connect an ammeter and a voltmeter to the motor to measure power consumption.
18. Conducting the test:
    • Start the pump, making sure there is no air in the system (deaeration).
    • Start with the outlet valve fully open (maximum flow).
    • Record the readings of the flow meter, manometers (pressure at the inlet P_in and output P_out), as well as the readings of electrical devices (current I, voltage U).
    • Gradually close the outlet valve, taking at least 5-7 measurements for different flow points until fully closed (zero flow). At each measurement point, wait for the readings to stabilize.
19. Data processing:
    • Calculate the pump pressure H for each point: H = (P_out - P_in) / (ρ * g) + ΔZ, where ρ is the density of the liquid, g is the acceleration of free fall, ΔZ is the height difference between the pressure measurement points.
    • Calculate the motor power consumption (if not measured directly) and the pump efficiency.
    • Plot the dependence curves of head (H), power (P) and efficiency (η) versus flow rate (Q).
    • Compare the obtained curves with the passport data of the pump (according to DSTU EN ISO 9906:2018). Deviations up to 5% are considered acceptable. Larger deviations require additional diagnostics.

6. Checklist after maintenance

7. Troubleshooting guide

8. Recommended maintenance schedule

9. Directory of spare parts

To order original spare parts and high-quality analogues, refer to the UNITEC-D electronic catalog: https://www.unitecd.com/e-catalog/

10. Links

• DSTU EN ISO 9905:2018 Industrial centrifugal pumps. Technical requirements.
• DSTU EN ISO 9906:2018 Operational tests of hydraulic characteristics. Acceptance classes for centrifugal, mixed flow and axial pumps.
• DSTU ISO 10816-3:2018 (EN ISO 10816-3:2009, IDT) Mechanical vibration. Evaluation of machine vibration based on measurement results on non-rotating parts. Part 3. Industrial machines with a rated power exceeding 15 kW and a rated speed exceeding 120 rpm (ISO 10816-3:2009, IDT).
• ISO 21049:2019 Pumps. End seals for centrifugal and rotary pumps.
• Instructions for operation and maintenance of pumps from the equipment manufacturer.