All About Water Pumps: Knowledge, Maintenance, and Servicing

Classification of water pumps:

 

It is not advisable to classify pumps by combining their operating principles with their applications, as this would lead to considerable confusion. Applications refer to the intended use, while principles refer to the underlying physics or mechanics; pumps based on different principles can often serve the same application, and the same pump can be used in different settings and for different purposes. For example, a mixed-flow pump is essentially an axial-flow pump that employs a mixed-flow impeller, meaning the direction of fluid discharge from the impeller is inclined relative to the pump shaft. In contrast, an axial-flow pump discharges fluid parallel to the shaft. Common categories of pumps include sewage pumps, chemical pumps, magnetic-drive pumps, oil pumps, fire-fighting pumps, vacuum pumps, diaphragm pumps, screw pumps, pipeline pumps, submersible pumps, reciprocating pumps, colloid mills, water supply and drainage equipment, hydraulic ejectors, control cabinets, and so on. Several examples are listed below for reference:

 

1. First, the broad categories are classified according to their operating principles:

 

1) Vane pump

 

Vane pumps can be classified into centrifugal pumps, mixed-flow pumps, axial-flow pumps, and vortex pumps.

 

Centrifugal pumps can further be classified into single-stage pumps and multi-stage pumps.

 

Single-stage pumps can be classified as single-suction pumps, double-suction pumps, self-priming pumps, and non-self-priming pumps, among others.

 

Multistage pumps can be classified as sectional-type and volute-type.

 

Mixed-flow pumps can be classified as volute-type or guide-vane-type.

 

Axial-flow pumps can be classified as either fixed-blade or adjustable-blade.

 

Vortex pumps can also be classified as single-suction pumps, double-suction pumps, self-priming pumps, non-self-priming pumps, and submersible pumps.

 

2) Positive-displacement pump

 

Positive-displacement pumps can be classified into reciprocating pumps and rotary pumps.

 

         Positive-displacement pumps operate by means of working elements that perform reciprocating or rotary motion within the pump cylinder, alternately increasing and decreasing the working volume to achieve the intake and discharge of liquid. Positive-displacement pumps in which the working elements move reciprocally are called reciprocating pumps, while those in which the working elements rotate are called rotary pumps. In the former, the suction and discharge processes alternate within the same pump cylinder and are controlled by suction and discharge valves; in the latter, the rotation of working elements such as gears, screws, vane rotors, or sliding vanes forces the liquid to flow from the suction side to the discharge side—this is the principle behind sewage pumps.

 

         Positive-displacement pumps deliver a constant flow rate at a given speed or stroke frequency, which is virtually independent of pressure. Reciprocating pumps, however, exhibit significant flow and pressure pulsations, necessitating the implementation of appropriate pulsation-damping measures. Rotary pumps, by contrast, generally produce little or no pulsation; diaphragm pumps also exhibit minimal pulsation. Diaphragm pumps possess self-priming capability, enabling centrifugal pumps to draw air out of the piping and subsequently suction liquid immediately upon startup. When starting a pump, the discharge-line valve must be fully opened. Reciprocating pumps are well suited for high-pressure, low-flow applications, whereas rotary pumps are ideal for medium- to low-flow rates at relatively higher pressures. Reciprocating pumps are particularly appropriate for conveying clean liquids or gas–liquid mixtures, making them suitable for use as chemical pumps. In general, positive-displacement pumps offer higher efficiency than dynamic (centrifugal) pumps.

 

3) Jet pump

 

         It relies on the high-speed jet generated by the working fluid to entrain the secondary fluid, and then, through momentum exchange, increases the energy of the entrained fluid.

 

         Dynamic pumps rely on the force exerted by a rapidly rotating impeller on the liquid to transfer mechanical energy to the fluid, increasing its kinetic and pressure energy. The pump casing then converts most of this kinetic energy into pressure energy, thereby achieving fluid delivery. Dynamic pumps are also known as impeller pumps or vane pumps.

 

Centrifugal pumps are the most common type of power-driven pump.

 

         Positive-displacement pumps have a limited head at a given speed; magnetic-drive pumps, on the other hand, exhibit a head that varies with flow rate. They operate steadily, and self-priming pumps provide continuous delivery with no pulsation in flow or pressure. However, most self-priming pumps lack inherent self-priming capability and must be initially filled with liquid or have their piping evacuated to a vacuum before operation can commence. Water pumps, by contrast, offer a broad range of practical applications and are well suited for conveying clean liquids with very low viscosity; specially designed models can handle slurry, sewage, and even mixtures of water and solid particles. Positive-displacement pumps are primarily used for water supply and drainage, irrigation, process fluid transfer, pumped-storage power generation, hydraulic transmission, and ship propulsion via water-jet systems, among other applications.

 

4) Other classifications of pumps

 

         In addition to classification by operating principle, pumps can also be classified and named according to other criteria. For example, based on the drive method, they can be categorized as electric pumps, steam-turbine pumps, diesel-engine pumps, and hydraulic-turbine pumps; based on their construction, as single-stage pumps and multi-stage pumps; based on their application, as boiler feedwater pumps and metering pumps; and based on the properties of the fluid being conveyed, as water pumps, oil pumps, and slurry pumps.

 

Working Principle and Characteristics of Water Pumps

 

I. Working Principle and Characteristics of Centrifugal Pumps

 

1) Working principle of centrifugal pumps

 

         Before starting the pump, the pump and the suction pipe must be completely filled with water. Once the pump is running, the high-speed rotation of the impeller generates centrifugal force, which flings the water in the impeller passages outward toward the volute casing, thereby pressurizing it. At the same time, a vacuum is created at the impeller inlet, drawing water from the reservoir through the suction pipe to replenish this space under atmospheric pressure. The water thus drawn in is then thrown outward by the impeller, passes through the volute casing, and enters the discharge pipe. It is thus evident that, as long as the centrifugal pump’s impeller continues to rotate, water can be continuously drawn in and discharged, enabling a steady flow of water to be lifted from a lower elevation to a higher one or conveyed over long distances. In summary, because a centrifugal pump relies on the centrifugal force generated by the high-speed rotation of its impeller to lift water to a higher elevation, it is called a centrifugal pump.

 

2) General characteristics of centrifugal pumps

 

(1) In a centrifugal pump, the water flows axially into the impeller and exits perpendicularly to the axial direction, meaning the inlet and outlet flow directions are at a 90° angle to each other.

 

(2) Since a centrifugal pump relies on the vacuum created at the impeller inlet to draw in water, the pump casing and suction pipe must be primed with water before starting, or a vacuum pump must be used to evacuate the air and establish a vacuum. In addition, the pump casing and suction piping must be tightly sealed to prevent any air leaks; otherwise, a vacuum cannot be formed, and the pump will be unable to draw in water.

 

(3) Since an absolute vacuum cannot be achieved at the impeller inlet, the suction lift of a centrifugal pump cannot exceed 10 meters. Moreover, accounting for the friction losses along the suction pipeline, the practical allowable installation height (i.e., the vertical distance between the pump shaft and the suction water surface) is considerably less than 10 meters. If the pump is installed too high, it will fail to prime; furthermore, because atmospheric pressure in mountainous areas is lower than in plains, the allowable installation height for the same pump must be reduced when it is installed in mountainous regions, especially at high altitudes, otherwise the pump will still be unable to draw water.

 

II. Working Principle and Characteristics of Axial-Flow Pumps

 

1) Working principle of axial-flow pumps

 

         Axial-flow pumps and centrifugal pumps operate on different principles; the former primarily relies on the thrust generated by the high-speed rotation of its impeller to lift water. As the blades of an axial-flow pump rotate, they generate lift on the water, pushing it from below upward.

 

         The impeller blades of an axial-flow pump are typically submerged in the water source reservoir. As the impeller rotates at high speed, the lift generated by the blades continuously pushes the water upward, forcing it to flow out through the discharge pipe. With the impeller rotating continuously, the water is steadily conveyed to a higher elevation.

 

2) General characteristics of axial-flow pumps

 

(1) In an axial-flow pump, water flows axially through the impeller—suction along the axis and discharge along the axis—hence the name “axial-flow pump.” (2) It features low head (1–13 meters), high flow rate, and high efficiency, making it well suited for irrigation and drainage in plain areas, lake regions, and river-network zones.

 

(3) No priming is required before startup, and operation is simple.

 

III. Working Principle and Characteristics of Mixed-Flow Pumps

 

1) Working principle of mixed-flow pumps

 

         Because the impeller of a mixed-flow pump has a shape that lies between those of a centrifugal pump and an axial-flow pump, its operating principle involves both centrifugal force and lift. Through the combined action of these two forces, the water exits the impeller at a certain angle relative to the shaft and is then conveyed upward through the volute casing and the discharge piping.

 

2) General characteristics of mixed-flow bouncing

 

(1) Compared with centrifugal pumps, mixed-flow pumps have a lower head and a larger flow rate; compared with axial-flow pumps, they have a higher head and a smaller flow rate. They are suitable for irrigation and drainage in plains and lake regions.

 

(2) In mixed-flow pumps, the water flows at a certain angle relative to the impeller shaft as it enters and exits the pump; hence they are also known as diagonal-flow pumps.

 

IV. Submersible Pumps, Submersible Pump Structure, and Submersible Pump Operating Principle

 

A submersible pump is also known as a submersible electric pump.

 

         Submersible pumps are versatile water-handling devices, widely used in both agricultural production and industrial processing. Based on their application scenarios and intended uses, they can generally be classified into submersible sewage pumps, sand-discharge submersible pumps, and clear-water submersible pumps.

 

         A submersible pump typically consists of a pump casing, a discharge pipe, a pump base, a submersible motor, and a starting protection device. Simply put, it is a machine that combines a pump and a motor to convey liquids; it features a simple structure and is easy to use.

 

Depending on the relative positioning of the pump and the motor, submersible pumps can be further classified into top-mounted and bottom-mounted types.

 

1. In the top-pump submersible pump configuration, the pump is located at the top and the motor at the bottom. This design significantly reduces the pump’s radial dimensions, making it well suited for well-driven submersible pumps and small-scale operational submersible pumps.

 

2. In a downhole submersible pump, the motor is located at the top and the pump at the bottom; such pumps are further classified into internal-mounted and external-mounted types.

 

⑴ In submersible electric pumps with an internal-mounted, downflow pump design, the liquid being conveyed first passes through the annular flow passage that surrounds the motor, thereby cooling the motor before exiting via the pump discharge outlet. Because this type of pump does not require concern about motor overheating even when operating in conditions close to dry suction, its range of applications is steadily expanding.

 

(2) In externally mounted, submersible centrifugal pumps with the pump body positioned below the motor, the liquid is discharged directly from the pressure chamber behind the impeller or from the outlet of the guide vane casing, and the motor is cooled by the pumped liquid. Because this bottom-mounted configuration allows the pump to operate in relatively shallow water, it is commonly used for submersible pumps employed at work faces; in particular, it is the primary structural design for large-diameter submersible pumps.

 

(3) In submersible electric pumps with a downpump configuration, the mechanical seal is located in the high-pressure zone of the outlet water flow; the higher the head, the greater the water pressure at this location, thereby subjecting the performance of the mechanical seal to head-dependent control.

 

V. Precautions and Characteristics of Pipeline Pump Operation

 

1. During operation, the bearing temperature of the pipeline pump must not exceed 35°C above ambient temperature, and the maximum temperature must not exceed 80°C.

 

2. Add bearing lubricating oil to the pump bearing housing, ensuring that the oil level is at the center line of the oil dipstick; the lubricating oil should be replaced or topped up promptly.

 

3. Unscrew the priming plug on the pump casing of the pipeline pump and fill it with priming water (or priming slurry).

 

4. Manually start the pipeline pump motor to verify that the motor is rotating in the correct direction.

 

5. Close the gate valve on the pipeline pump discharge line, as well as the outlet pressure gauge and the inlet vacuum gauge.

 

6. Start the pipeline pump motor. Once the pump is running normally, open the outlet pressure gauge and the inlet vacuum gauge; after they indicate appropriate pressures, gradually open the gate valve while monitoring the motor load.

 

7. Whenever possible, operate the pipeline pump within the flow rate and head ranges specified on its nameplate to ensure it runs at its best efficiency point, thereby achieving the greatest energy-saving effect.

 

8. When shutting down the pipeline pump, first close the gate valve and pressure gauge, then stop the motor.

 

9. If any abnormal noise is detected in the pipeline pump, stop the pump immediately and investigate the cause.

 

10. Inspect the pipeline pump, piping, and joints for any looseness. Manually rotate the pipeline pump to check whether it operates smoothly.

 

11. Regularly inspect the wear condition of the pipeline pump shaft sleeve and replace it promptly if significant wear is detected.

 

12. During the first month of operation, the pipeline pump’s lubricating oil shall be changed after 100 hours; thereafter, the oil shall be changed every 500 hours.

 

13. If a pipeline pump is to be left idle for an extended period, it must be completely disassembled, thoroughly dried, and all moving parts and mating surfaces lubricated with grease before reassembly and proper storage.

 

14. When a pipeline pump is operated during the cold winter months, after shutdown, the drain plug at the bottom of the pump casing must be unscrewed to completely drain the conveyed medium, thereby preventing freezing and cracking.

 

15. Regularly adjust the packing gland of the pipeline pump to ensure proper dripping from the packing chamber.

 

VI. Procedures for Regular Pump Maintenance

 

1. Purpose

 

Ensure that the water pump is always in good operating or standby condition.

 

2. Scope of Application

 

All residential water pumps, fire pumps, sprinkler pumps, pressure-boosting pumps, sewage pumps, and air-conditioning water pumps installed in the buildings.

 

3. Responsibilities

 

Regular maintenance of the water pump shall be performed by the maintenance personnel of the management office.

 

4. Content

 

1) The domestic water pump and the air-conditioning water pump shall undergo routine inspection and maintenance once a week, and a comprehensive overhaul once every six months.

 

2) The fire pump and sprinkler pump shall be put through a trial run once a month, and the pressure-boosting pump once every two months, with each run lasting 10–15 minutes. During fire pump startup, the water spray from the test fire hydrant at the top of the piping network shall achieve a range of at least 6 meters. A comprehensive maintenance inspection shall be conducted every six months.

 

3) Sewage pumps and submersible pumps shall undergo a comprehensive maintenance inspection every six months.

 

4) During pump maintenance, valves, pressure gauges, pipelines, and other components within a 2-meter range connected to the pump body shall be serviced concurrently with the pump.

 

5) Pump Body Maintenance

 

⑴ Inspect the pump casing for any damage, ensure the nameplate is intact, verify that the water flow direction indicator is clear and legible, and confirm that the exterior is clean and the paint is undamaged.

 

(2) Top up the lubricating oil; if the oil has discolored or contains impurities, it should be replaced.

 

⑶ Inspect the gland packing for leaks; if leakage is detected, add or replace the asbestos rope packing.

 

(4) If the coupling bolts and rubber pads are damaged, they shall be replaced.

 

⑸ Tighten the base mounting bolts and apply rust-proofing treatment.

 

⑹ Due to frequent operation, the bearings at both ends of the coupling for the domestic water pump and the air-conditioning water pump shall be disassembled annually for cleaning or replacement.

 

6) Motor Maintenance

 

⑴ Visual inspection shall reveal a clean appearance, an intact nameplate, and proper grounding connections.

 

⑵ Disconnect the wire connection links inside the motor junction box, and use a 500 V megohmmeter to measure the insulation resistance between motor winding phases and between each phase and ground; the measured value shall not be less than 0.5 MΩ.

 

⑶ The three-phase leads and connecting links inside the motor junction box shall be securely fastened and tightly connected.

 

7) Maintenance of relevant valves, pipelines, and accessories

 

⑴ The opening and closing of each valve shall be flexible and reliable, with no internal or external leakage.

 

(2) The check valve shall operate smoothly, with no water leakage inside or outside the valve body.

 

⑶ The pressure gauge provides accurate readings and has a clear dial.

 

(4) The pipeline and all associated accessories shall have a clean and aesthetically pleasing exterior, free from cracks, and the paint coating shall be intact and free from flaking.

 

⑸ Perform a jog test to verify that the pump is rotating in the correct direction; if not, make the necessary correction.

 

8) Maintenance of the control cabinet

 

⑴ Disconnect the main power supply to the control cabinet and inspect all transfer switches; the start and stop buttons shall operate smoothly and reliably.

 

⑵ Inspect the circuit breakers, contactors, relays, and other electrical components inside the cabinet to ensure they are in good condition, and tighten the wiring screws on all electrical contacts and terminal blocks.

 

⑶ Clean dust from both the inside and outside of the control cabinet.

 

⑷ Close the main power supply and verify that the power indicator is functioning normally.

 

9) After maintenance is completed, start the water pump and observe whether the ammeter and indicator lights are functioning normally.

 

10) Observe that the pump operates smoothly, with no obvious vibration or abnormal noise; the pressure gauge reading is normal; and there are no unusual noises from any electrical components in the control cabinet.

 

5. Major Pump Maintenance Items

 

Maintenance Items and Requirements for SB Single-Suction Clean Water Centrifugal Pumps

 

Operational Requirements and Technical Requirements

 

1) Inspect the stuffing box

 

When this pump is sealed with a packing gland, it is essential to ensure the packing is properly tightened. If the packing is too loose, excessive leakage will impair performance; under normal operating conditions, the leakage should be approximately 60 drops per minute—dropping at this rate is acceptable, but any significant splashing around the packing indicates an abnormal condition.

 

2) Inspect the mechanical seal

 

When this pump is equipped with a mechanical seal, it is strictly forbidden to operate without water supply; during commissioning, only brief jog starts are permitted. Under normal operating conditions, a small amount of water will drip from the front of the water-retaining ring. If the leakage becomes excessive, the friction rings should be inspected and the mechanical seal overhauled or replaced as necessary. The service life of the mechanical seal under normal conditions is approximately 8,000 hours; in most cases, it is not necessary to replace the entire seal—simply replacing the rotating and stationary friction rings is sufficient.

 

3) Lubricate the bearing

 

This pump is equipped with semi-enclosed, imported SKF bearings that are pre-lubricated with high-temperature grease at the factory. It can operate continuously for two years, after which lubrication with grease is required once annually.

 

4) Inspect the impeller and remove any foreign objects.

 

In the event of special circumstances, such as damage to the pump impeller or foreign objects being lodged in it, requiring inspection and cleaning, the bearing housing and rear cover must be removed, and the shaft and impeller pulled out toward the rear; the pump casing and inlet and outlet nozzles do not need to be disassembled.

 

5) Inspect wear parts

 

The pump’s primary wear parts include the flexible coupling, mechanical seal, stationary and rotating rings, O-ring rubber seals, bearings, impeller nuts, and packing gland plates. During maintenance, these components should be carefully inspected, and any damaged parts应及时 replaced.

 

VII. Maintenance and Care of Submersible Sewage Pumps

 

Due to the unique operating conditions of submersible sewage pumps, regular inspection and maintenance are essential to ensure their proper operation and long service life:

 

1. Replace the sealing ring: After prolonged operation in sewage media, the clearance between the impeller and the sealing ring may increase, leading to reduced pump flow and efficiency. In this case, switch off the power supply, lift the pump out of the well, remove the bottom cover, and take out the sealing ring. Then, select a new sealing ring that matches the actual dimensions of the impeller throat ring; the recommended clearance is typically around 0.5 mm.

 

2. When a submersible sewage pump is not used for an extended period, it should be cleaned, lifted out of the water, and stored in a well-ventilated, dry location, taking care to protect it from freezing. If the pump is kept submerged, it must be operated for at least 30 minutes every 15 days (without allowing it to run dry) to verify its functionality and operational suitability.

 

3. Cables shall be inspected at least once annually; if damaged, they must be replaced.

 

4. Inspect the motor insulation and tightening bolts at least once a year. If the motor insulation has deteriorated, have it repaired by a qualified technician; if any tightening bolts are loose, retighten them.

 

5. Prior to shipment, the submersible sewage pump is pre-filled with an appropriate amount of lubricating oil to ensure proper lubrication of the mechanical seal; this oil should be inspected annually. If water is detected in the oil, the oil must be drained, the oil replaced, the sealing gasket replaced, and the drain plug tightened. Three weeks later, a re-inspection is required; if the oil has again turned into an emulsion, the mechanical seal must be inspected and, if necessary, replaced.

 

6. If a submersible sewage pump malfunctions during operation, follow the troubleshooting procedures provided. If the problem persists and the cause remains unidentified, do not attempt to disassemble or repair the pump yourself; instead, immediately contact a qualified technician for service.