Double Suction Centrifugal Pump

The efficiency of a centrifugal pump is the product of three efficiencies: mechanical, volumetric, and hydraulic. The efficiency of a pump set is the product of the pump efficiency and the motor efficiency. The main factors causing low efficiency of a centrifugal pump set include the following:
1. The efficiency of the pump itself is the most fundamental factor. Under the same working conditions, the efficiency of the pump can differ by more than 15%.
2. The operating condition of the centrifugal pump is lower than its rated condition, resulting in low pump efficiency and high energy consumption.
3. The efficiency of the motor remains basically unchanged during operation. Therefore, choosing a high-efficiency motor is of crucial importance.
4. The influence of mechanical efficiency is mainly related to design and manufacturing quality. After selecting the pump, the later management has a relatively small impact.
5. Hydraulic losses include hydraulic friction and local resistance losses. After the pump has run for a certain period of time, inevitable wear of the surface of the impeller and guide vanes occurs, resulting in increased hydraulic losses and reduced hydraulic efficiency.
6. The volumetric loss, also known as leakage loss, includes three types of leakage losses: the sealing ring of the impeller, the gap between stages, and the axial force balance mechanism. The efficiency of volumetric efficiency is not only related to design and manufacturing but also to later management. After the pump operates for a certain period of time, due to friction between components, the gap increases, and the volumetric efficiency decreases.
7. Due to clogging of the filter cylinder, pipeline air intake, etc., the centrifugal pump becomes empty or runs in idle mode.
8. Before starting the pump, employees do not pay attention to the preparatory work before starting the pump, such as warming up the pump, rotating the pump, and filling the pump, and the basic operating procedures are not carried out thoroughly. This often causes cavitation of the pump, resulting in high noise, vibration, and low pump efficiency.
II. Measures to reduce the energy consumption of centrifugal pumps and improve the efficiency of the pump set
Use high-molecular composite materials for repair and protection:
Energy-saving principle: During the operation of the pump, the water flowing inside the pump is affected by the friction between it and the flow channel and the surface of the pump impeller, as well as the viscosity of the water. The energy consumed by the pump is mainly used to resist the flow friction force and vortex resistance of the water. The energy consumed by the water during its flow (head loss) is used to overcome the internal friction force and the friction force between the water and the equipment interface. If the surface of the pump and the impeller are smooth (such a surface is called a hydrodynamic smooth surface), the surface resistance is small, and the energy consumed is less. By spraying high-molecular composite materials on the over-flow surface and the impeller, a hydrodynamic smooth surface is formed on the surface, with a surface smoothness 20 times that of stainless steel after polishing. This extremely smooth surface reduces the stratification of fluid inside the pump, thereby reducing internal turbulence, reducing volumetric losses and hydraulic losses, reducing power consumption, and achieving the purpose of reducing flow resistance losses, thereby improving the hydraulic efficiency of the pump, and to a certain extent, also improving mechanical efficiency and volumetric efficiency. The density of the molecular structure of the coating can isolate the contact between air, water, etc. and the pump impeller base material, minimizing electrochemical corrosion and rust.

1. Leakage occurred during static test. After the mechanical seal is installed and debugged, a static test is usually conducted to observe the leakage. If the leakage is small, it is usually due to problems with the moving or stationary ring sealing rings; if the leakage is large, it indicates problems between the moving and stationary ring friction pairs. Based on the initial observation of the leakage volume and the determination of the leakage location, manual turning of the shaft can be performed to observe further. If there is no significant change in the leakage volume, it indicates problems with the sealing rings of the moving and stationary rings; if the leakage volume changes significantly during turning, it can be determined that there are problems with the friction pairs of the moving and stationary rings; if the leakage medium jets axially, the moving ring sealing ring is more likely to have problems; if the leakage medium sprays in all directions or leaks from the water cooling holes, it is mostly due to the failure of the stationary ring sealing ring. In addition.
There may also be leakage channels, but there is usually a primary and secondary distinction. As long as the observation is meticulous and the structure is familiar, the problem can be correctly determined.
2. Leakage during trial operation. After the mechanical seal for the pump has undergone static test, during the high-speed rotation caused by the centrifugal force generated during operation, the leakage of the medium will be suppressed. Therefore, the leakage of the mechanical seal during trial operation, after excluding the failure of the shaft seal and the end cover seal, is mostly caused by the damage to the friction pairs of the moving and stationary rings. The factors causing the failure of the friction pair sealing include:
(1) During operation, due to abnormal phenomena such as vacuum, cavitation, or prolonged pressure build-up, a large axial force is generated, causing the contact surfaces of the moving and stationary rings to separate;
(2) Excessive compression during the installation of the mechanical seal leads to severe wear and scratches on the end faces of the friction pairs;
(3) The moving ring sealing ring is too tight, and the spring cannot adjust the axial floating amount of the moving ring;
(4) The stationary ring sealing ring is too loose, and when the moving ring undergoes axial floating, the stationary ring detaches from the stationary ring seat;
(5) There are granular substances in the working medium, which enter the friction pair during operation, and the sealing ends are inspected by flaw detection;
(6) There is an error in the design or selection, the contact pressure of the sealing end face is too low, or the cold shrinkage property of the sealing material is too large. These phenomena often occur during trial operation, and sometimes they can be eliminated by appropriate adjustments to the stationary ring seat, etc., but most require reinstallation and replacement of the seals.
3. Leakage suddenly occurs during normal operation. For centrifugal pumps, sudden leakage during operation is mostly caused by normal wear or reaching the service life; most of the time, it is caused by significant changes in operating conditions or improper operation and maintenance.
(1) Vacuum, cavitation, or prolonged pressure build-up causes the seal to be damaged;
(2) The actual output of the pump is too small, and a large amount of medium circulates within the pump, causing heat accumulation. The medium vaporizes, leading to seal failure;
(3) The return flow is too large, causing sediment at the bottom of the container (tower, tank, drum, pool) to rise on the suction side of the pump.
It damages the seal;
(4) The pump has been stopped for a long time.
Manual turning of the shaft was not performed during restart.
The friction pair is torn due to adhesion and damage to the sealing surface;
(5) The medium contains more corrosive, polymerizing, or gelling substances;
(6) The environmental temperature changes sharply;
(7) The operating conditions change frequently or are adjusted;
(8) Sudden power outage or machine failure shutdown. If the leakage of the centrifugal pump during normal operation is not detected in time, it may lead to major accidents or losses, and it is necessary to pay attention and take effective measures. Note:
The discovery of problems and the solutions to them all come from daily practical work, just like the internal structure of a single-stage double-suction centrifugal pump. It cannot be fully understood merely by imagination; only by disassembling it and analyzing it based on theoretical knowledge can one master it well.
Understand the functions of each part of the structure and why problems occur.
The most important structure of a single-stage double-suction centrifugal pump is the impeller and the sealing body, which are also the components most prone to failure.
For example, once the shaft seal breaks, there will be problems such as water leakage, and in severe cases, it can damage the equipment, thereby affecting production. Regarding the issue of the shaft, generally, as long as the coaxiality is adjusted properly, there will not be too many problems.
Therefore, very high requirements have been put forward for the working principle and usage method of the dial indicator.
In simple terms, everything depends on the combination of theory and practice, which is indispensable. For the installation of the sealing body, only by doing it yourself can you master the techniques involved.

I. Pre-installation Preparation: Parameter Verification and Site Planning
Basic Parameter Confirmation
Verify the matching degree of the pump model with actual requirements: For example, the lift height needs to cover the terrain height difference + pipeline loss (e.g., irrigation field height difference of 20m, pipeline length of 300m, total lift height ≈ 20m + 15m = 35m, choose the 200S42 model).
Check the completeness of the equipment: Are the pump body, impeller, bearing assembly, sealing components (packing / mechanical seal), coupling protective cover and other accessories complete? Are there any cracks or wear on the surface?
Installation Site Requirements
Foundation Flatness: Horizontal error ≤ 0.5mm/m, use concrete foundation (thickness ≥ 200mm), pre-buried anchor bolts (spacing according to the pump base hole spacing).
Space Reservation: A 1.5-2m maintenance passage needs to be reserved around the pump, and a lifting device should be set above (when the pump weight > 500kg), to facilitate the disassembly of the pump cover and impeller.
II. Core Installation Steps: From Positioning to Trial Run
(1) Pump and Motor Positioning Installation
Base Fixation
Base leveling: Use a level gauge to adjust the levelness of the base (lateral / longitudinal deviation ≤ 0.1mm/m), pre-tighten the anchor bolts first, and then tighten them again after the pump body installation.
Damping Measures: If installed on a mobile pump truck or in a vibrating environment, place rubber damping pads under the base (thickness 5-10mm) to avoid resonance.
Pump Body and Motor Connection
Single-suction Pump Installation: Place the pump body on the base, insert the anchor bolts, do not tighten immediately; lift the motor to the coupling side and initially fix it.
Alignment Calibration (Key!) ：
Measure the radial / end face runout of the coupling using a dial indicator (allowable error ≤ 0.05mm). Adjust by adding or removing the motor base gaskets (the gaskets should be ≥ 3 layers, with a total thickness of ≤ 5mm).
Example: The coupling of the 250S65 pump has a diameter of 200mm. When the end face runout exceeds 0.08mm, a 0.1mm copper gasket needs to be added at the bottom of the motor for correction.
(II) Pipeline System Connection
Installation of suction pipe system
Pipe diameter requirements: The diameter of the suction pipe should be greater than or equal to the diameter of the pump's suction port (for example: if the pump's inlet diameter is DN200, the suction pipe should be selected as DN250), and the slope of the pipeline to reduce resistance: uphill towards the pump at a ratio of 1:50 (to avoid air pockets), and it is strictly prohibited to have a "U-shaped" bend; the bottom valve should be at least 1.5 times the pipe diameter away from the bottom of the pool, and at least 0.5 meters away from the water surface.
Filter net configuration: Install a filter net at the suction inlet (with a pore size of ≤ 5mm) to prevent debris from being sucked in (if the cement sand content in the irrigation channel is high, a metal filter net should be selected).
Installation of pressure water pipeline
Check valve and gate valve: Install the gate valve (for convenient flow regulation) and the check valve (to prevent water hammer when the pump stops) in sequence at the outlet, with a distance of at least 5 times the pipe diameter from the pump outlet.
Installation of pressure gauge: Install a pressure gauge before the gate valve at the pump outlet (with a range of 1.5 times the designed head), to monitor the operating pressure in real time.

500 hours (approximately 3 months)
Replace bearing lubricant: Clean the bearing chamber, rinse with kerosene, and then inject new grease (the model must match the original specification).
Check packing wear: When the wear depth of the packing gasket cover is greater than 2mm, replace it (the material can be selected as vegetable oil packing or carbon fiber packing).
2000 hours (approximately 1 year)
Disassemble the pump for maintenance: Open the pump cover, check the gap between the impeller and the sealing ring (the standard value is 0.15-0.3mm, and if the wear exceeds 0.5mm, replacement is required).
Measure shaft diameter wear: When the wear at the shaft neck is greater than 0.1mm, it can be repaired by electroplating or replaced with a new shaft (for example, for the 200S pump shaft with a diameter of 45mm, the allowable wear is ≤0.2mm).
Long-term inoperative (more than 1 month)
Empty the liquid in the pump: Remove the bottom cover, dry the pump chamber with compressed air to prevent rusting (pay special attention to anti-freezing in winter).
Anti-rust treatment: Apply anti-rust oil to the impeller and shaft surfaces, inject lubricating grease into the bearing chamber, and wrap the entire machine with plastic sheet.

Start-up sequence: Close the outlet gate valve → Start the motor → Wait for the speed to stabilize and then slowly open the gate valve (the full opening time should be no more than 2 minutes to avoid motor overload).
Shutdown sequence: Close the outlet gate valve → Cut off the power supply → If it is a long-term shutdown, empty the liquid in the pump.
Anti-surge measures: The suction height should be ≤ 5m (for normal temperature clear water), and when the water temperature is > 40℃, the installation height needs to be reduced (calculated according to the NPSH value for cavitation).

I. Quality Assurance
Before choosing a wholesale double-suction pump, it is essential to pay attention to the quality issue. As a high-load and high-speed equipment, if the quality is not up to standard, there may be safety problems such as water leakage and electric leakage. It is recommended to choose double-suction pumps from well-known brands, such as Grundfos Pumps and Ametek Pumps. These brands all have a high quality guarantee.
II. Brand Selection
When choosing a brand, it is advisable to select a brand with a good reputation. These brands usually have a complete after-sales service system, which can provide users with better services. At the same time, brands with good reputations usually have a high market recognition and can meet the needs of users.
III. After-sales Service
When choosing a wholesale double-suction pump, it is necessary to pay attention to the after-sales service. As a high-load equipment, there may be some problems that require maintenance by after-sales personnel. Therefore, when choosing a brand, it is necessary to choose a brand with a complete after-sales service system. This can ensure that during the use of the double-suction pump, timely and effective assistance can be obtained.
IV. Price Selection
When choosing a wholesale double-suction pump, price is also an important consideration. It is recommended to choose double-suction pump products with good cost performance. However, price is only one factor and cannot be the sole criterion. It is necessary to comprehensively consider factors such as quality, brand, and after-sales service, and make a comprehensive judgment.
V. Application Scenarios
Before choosing a wholesale double-suction pump, specific application scenarios need to be considered. Different application scenarios require different double-suction pump products. For example, if it is used for water treatment in the industrial field, a double-suction pump that can withstand high pressure and high temperature needs to be selected. If it is used for water treatment in the household field, a small-sized double-suction pump can be chosen.