Construction, selection, maintenance, and assembly and disassembly techniques for pipeline pumps

Basic structure of pipeline pumps

The basic structure of a pipeline pump is composed of six parts: impeller, pipeline pump body, pump shaft, bearing, sealing ring, and packing box.

According to different installation methods, it can be divided into vertical pipeline pumps and horizontal pipeline pumps. The common letters are ISG and ISW

1. The impeller is the core part of a centrifugal pump, with high rotational speed and high output. The blades on the impeller play a major role, and the impeller needs to undergo static balance experiments before assembly. The inner and outer surfaces of the impeller should be smooth to reduce friction losses caused by water flow.

2. The pipeline pump body, also known as the pump casing, is the main body of the water pump. It plays a supporting and fixing role and is connected to the bracket for installing bearings.

3. The function of the pipeline pump shaft is to connect the coupling with the motor, transmitting the torque of the motor to the impeller, so it is the main component for transmitting mechanical energy.

4. Bearings are components that are placed on the pump shaft to support the pump shaft, and there are two types of bearings: rolling bearings and sliding bearings. Rolling bearings should be lubricated with butter, which is generally 2/3-3/4 of the volume. If the volume is too large, it will generate heat, and if it is too small, there will be noise and heat! The sliding bearing uses transparent oil as a lubricant and is filled to the oil level line. Too much oil will seep out and float along the pump shaft, and too little bearing will overheat and burn out, causing accidents! During the operation of the water pump, the maximum temperature of the bearing is 85 degrees Celsius, usually around 60 degrees Celsius. If it is too high, it is necessary to find the cause (whether there are impurities, whether the oil is black, whether there is water ingress) and promptly handle it!

5. Sealing ring, also known as leak reducing ring. Excessive clearance between the impeller inlet and the pump casing can cause water in the high-pressure area of the pump to flow through this clearance to the low-pressure area, affecting the pump's water output and reducing efficiency! Excessive clearance can cause friction and wear between the impeller and pump casing. In order to increase reflux resistance and reduce internal leakage, and prolong the service life of the impeller and pump casing, a sealing ring is installed at the junction of the inner edge of the pump casing and the outer support of the impeller, and the sealing gap should be kept between 0.25 and 1.10mm.

6. The packing box mainly consists of packing, water seal ring, packing cylinder, packing gland, and water seal pipe. The main function of the packing box is to seal the gap between the pump casing and the pump shaft, preventing the water flow inside the pump from flowing outside and preventing external air from entering the pump. Always maintain a vacuum inside the water pump! When the friction between the pump shaft and the packing generates heat, the water seal pipe needs to hold the water inside the water seal ring to cool the packing! Maintain the normal operation of the water pump. So during the operation inspection of the water pump, special attention should be paid to the inspection of the packing box! The packing needs to be replaced after about 600 hours of operation.

Principles and steps for selecting pipeline pumps

Relatively speaking, pipeline pumps do not have high requirements for flow rate and the medium they transport. Therefore, the selection of pipeline pumps mainly depends on the appropriate flow rate and head. The selection of pipeline pumps is mainly based on the process flow, water supply and drainage requirements. Atlantic Pump Industry believes that it mainly considers five aspects, including liquid delivery volume, device head, liquid properties, pipeline layout, and operating conditions.

1、 First, list the basic data:

1. Characteristics of the medium: medium name, specific gravity, viscosity, corrosiveness, toxicity, etc.

2. What is the particle diameter and content of the solid contained in the medium.

3. Medium temperature: (℃)

4. The required flow rate for industrial pumps can generally ignore the leakage rate in the pipeline system during the process flow, but the impact of process changes on the flow rate must be considered. If agricultural pumps use open channels for water transportation, leakage and evaporation must also be considered.

5. Pressure: suction pool pressure, drainage pool pressure, pressure difference (head loss) in the pipeline system.

6. Pipeline system data (pipe diameter, length, type and number of pipeline accessories, geometric elevation from suction tank to pressure tank).

If necessary, a device characteristic curve should also be made.

Secondly, when designing and arranging pipelines, the following precautions should be taken:

A. Reasonable selection of pipeline diameter can result in small resistance loss under the same flow rate and small liquid flow velocity. However, the high price and small pipeline diameter can lead to a sharp increase in resistance loss, resulting in an increase in the head of the selected pump, an increase in belt power, and an increase in cost and operating expenses. Therefore, comprehensive consideration should be given from both technical and economic perspectives.

B. The discharge pipe and its joints should consider the maximum pressure they can withstand.

C. The pipeline layout should be arranged as straight as possible, minimizing the number of accessories in the pipeline and minimizing the length of the pipeline. When 

turning is necessary, the bending radius of the elbow should be 3-5 times the diameter of the pipeline, and the angle should be greater than 90 ℃ as much as possible.

D. The discharge side of the pump must be equipped with valves (ball valves or globe valves, etc.) and check valves. The valve is used to adjust the operating point of the pump, and the check valve can prevent the pump from reversing when the liquid flows backwards and prevent the pump from being hit by water hammer. (When the liquid flows backwards, a huge reverse pressure will be generated, causing damage to the pump)

2、 Determination of pipeline pump flow head and flow rate

a. If the minimum, normal, and maximum flow rates have been given in the production process, the maximum flow rate should be considered.

b. If only normal flow rate is given in the production process, a certain margin should be considered.

For large flow low head pumps with ns>100, a flow margin of 5% is taken. For small flow high head pumps with ns<50, a flow margin of 10% is taken. For pumps with ns ≤ 50, a flow margin of 5% is also taken. For pumps with poor quality and operating conditions, a flow margin of 10% should be taken.

c. If the basic data only provides weight flow rate, it should be converted to volume flow rate.

Use and maintenance of pipeline pumps

1. After every 500 hours of operation, loosen the screw plug on the sealing seat and use a syringe to extract residual oil from the cavity; Fill the sealing chamber with qualified No. 20 mechanical oil to half the volume of the chamber (a suitable inspection method for adding oil is to run the oil pump and ensure that the oil does not spill out); Tighten the screw plug to prevent leakage.

2. When it is found that the mechanical noise of the motor increases and the temperature rise at the bearings is abnormal, the lubrication of the motor bearings should be checked. If the lubricating grease changes color or becomes dirty, it should be replaced in a timely manner.

3. When oil leakage is found in the sealing seat, the screw plug on the sealing seat can be loosened and the oil pump can be operated. When there is oil gushing out and there is a smell of aviation oil, it can be determined that the mechanical seal has failed. Stop using the pipeline pump in order to quickly replace the mechanical seal.

4. Replace the failed mechanical seal

Key points for using pipeline pumps:

(1) Test run work: Check if the connecting parts are loose; Rotate the coupling by hand to rotate the rotor several times, check if the unit rotates flexibly, if there is any noise or uneven feeling of weight, to determine whether there are foreign objects inside the pump or if the shaft is bent, and if the seal is installed correctly or not; Check whether the clean No. 20 lubricating oil in the sealing chamber is filled with 1/2 of the chamber space; Whether the surface of the pump unit is clean; Unit turning no-load test.

(2) Manual start: Fill the pump (for the first time), slightly open the outlet valve, start the motor, and when the pressure rises and it is confirmed that the pump unit is running smoothly, gradually open the outlet valve to meet the operating requirements.

(3) Operation inspection: When the pump is operating normally at power frequency (variable frequency), the readings of the pump set ammeter, voltmeter, inlet and outlet vacuum gauge, pressure gauge, and flow meter should be regularly checked and recorded. Is the vibration, noise, temperature rise, etc. of the unit normal. There should be no obvious aviation oil leakage at the shaft seal.

(4) Normal shutdown: Close the discharge valve, lightly load the pump, and stop the motor.

5. Emergency parking conditions:

(1) Pump (such as vertical pipeline pump, pipeline centrifugal pump, etc.) motor operating ammeter indication is abnormal (excessively large or becoming few); The pump system makes abnormal noises.

(2) The inlet vacuum pressure gauge and outlet pressure gauge of the pump have abnormal indications, causing significant vibration and abnormal noise on the pump body, resulting in a serious decline in performance.

(3) The pump motor produces odor, aviation oil leaks from the shaft seal, and the bearing temperature exceeds 75 degrees Celsius.

Ten tips for assembling and disassembling pipeline pumps

Below is a detailed introduction to the top ten techniques for assembling and disassembling pipeline pumps.

Before assembling the pipeline pump, all parts should be inspected, and the mating surface of the parts, especially the friction surface of the mechanical seal, should be cleaned. The sealing surface should not have obvious scratches, cracks, bumps and other defects. If there are any of the above defects, they should be replaced.

Assembly:

1. Press the water deflector onto the motor shaft and fasten the middle seat onto the motor with bolts.

2. After applying lubricant such as Vaseline to the rubber ring of the mechanical seal static ring, press the static ring component into the middle seat along the axis, apply clean grease on the sealing surface, install other sealing components, install flat keys, impellers, and stop washers, and tighten them with bolts.

Attention: The sealing rubber ring of the mechanical seal stationary ring is prone to deviation during installation, which will cause leakage of the mechanical seal. It should be carefully checked during installation.

Apply an appropriate amount of grease to the sealing end face of the middle seat and install the O-ring. When installing the O-ring, the sealing ring is prone to detachment and folding, please be careful not to cause water leakage.

3. Lift the motor assembly, place the impeller downwards and slowly insert it into the pump body. Then tighten it with bolts and install each pipe plug and vent plug.

4. Rotate the rotor by hand and check for any jamming.

Installation:

1. When installing, the closest location to the conveying liquid should be selected, so that the pump is installed at the location with the minimum suction height and the shortest suction pipeline

Attention: It should be ensured that the distance between the unit and surrounding obstacles is greater than 150 mm, so that the motor fan has sufficient air source.

2. When the pump is used in areas with strict vibration requirements, shock absorbers (pads) can be used and must be installed according to the manufacturer's instructions.

3. The installation of the pipeline should be reliably fixed, and the pipeline support close to the pump flange should have sufficient rigidity to prevent the pump from bearing the weight and pressure of the pipeline.

4. The installation of the pump unit should avoid direct sunlight and rain.

5. A vacuum pressure gauge should be installed at the inlet of the pump, and a pressure gauge should be installed at the outlet flange to observe and control the operation of the pump. The range of the pressure gauge should be 2-3 times the actual pressure.

6. The inlet and outlet pipelines of the pump should be equipped with gate valves for easy maintenance and operation adjustment.

7. Wiring: It is necessary to correctly wire according to the requirements of the nameplate. When wiring, the terminals must be firm and not loose, otherwise it may cause poor contact and lead to phase loss and burning of the machine. To ensure the reliable operation of the motor, an overload protection device should be installed at the electrical switch, and the setting value of the protection device should be adjusted according to the current requirements on the motor nameplate.

Warning: If an overload protection device is not installed, it may cause the motor to burn out due to overload when the outlet valve is fully open, excessive flow operation, or sudden increase in current under certain circumstances.

8. In the suction state (water level lower than the impeller axis or water level lower than the pump suction inlet axis), at standard atmospheric pressure, the installation height of the pump H is 10- (NPSH) r-0.5 hw, where hw is the resistance loss of the suction pipeline (calculation unit in the formula: m).

9. When pumping water from a pool, the length of the straight pipe section in front of the pump suction port should not be less than 3 times the inlet diameter, and the depth of the suction pipe mouth submerged under the water surface should be greater than 1.5 times the inlet diameter and not less than 500 mm. The distance between the suction pipe inlet and the tank wall should be greater than 1.5 times the diameter, and the distance from the tank bottom should be greater than 1.5 times the diameter and not less than 500mm. A filter screen should be installed, and the total area of the filter screen should not be less than 2-3 times the area of the suction pipe inlet.

Attention: The installation of the horizontal section of the suction pipe should be slightly tilted downwards against the water flow direction to prevent air pockets.

10. In order to facilitate the filling of water into the pump before starting, a bypass valve can be added at both ends of the check valve. Before starting the pump, open the bypass valve to fill the pump, and then close it after filling, making it convenient for use. For pumps used for water supply in high-rise buildings or with an outlet pressure greater than 0.2MPa, in addition to installing a gate valve at the outlet, a check valve should also be installed between the pump outlet and the gate valve to prevent sudden power outage and high-pressure water backflow from causing impeller damage.

Disassembly:

Follow the reverse steps of installation.

Attention: When disassembling the mechanical seal, it is not allowed to directly hit the static ring with a hammer or iron hammer. Instead, gently tap with wood and slowly remove the static ring. If dirt accumulation makes disassembly difficult, it should be cleaned first before disassembly.