How to choose the suck pump set?

In real dredging and construction projects, the sand suction pump unit is a highly utilized piece of equipment, particularly when employed as a relay pump unit. How familiar are you with sand suction pumps? How does one go about selecting appropriate sand suction pump equipment for real-world working conditions? In this article, we’ll explore the critical factors involved in choosing sand suction pump units and their accompanying water pump units.

A. Suck Pump Selection Conditions

1. Physical and chemical properties of the conveying medium

The physical and chemical properties of the conveying medium directly affect the performance, material and structure of the suck pump, which is an important factor to be considered when selecting a suck pump model. For example, medium name, medium properties (corrosivity, abrasiveness, toxicity, etc.), solid particle content and particle size, density, viscosity, vaporization pressure, gas content, crystallization, etc.

2. Process parameters (important basis for selection)

1. Flow Q:In the production of process equipment, to get the amount of medium conveyed by the suck pump, the process personnel should generally give the normal, minimum and maximum flow.
2. Often only the normal and rated flow of the suck pump is shown on the suction pumpdata sheet.When choosing a suck pump, the rated flow is required to be no less than the maximum flow of the pump machine, or according to 1.1 to 1.15 times the normal flow.
3. Head H: The head value required by the process device, also known as the calculated head. Generally, the rated head is required to be 1.05 to 1.1 times the head required by the pump device.Inlet pressure Ps and outlet pressure Pd: Inlet and outlet pressure refers to the pressure at the flange of the inlet and outlet connecting pipe of the suck pump. The size of the inlet and outlet pressure affects the pressure resistance of the pump casing and the requirements of the shaft seal.
4. Temperature T: The temperature of the pump inlet medium. Generally, the normal, minimum and maximum temperatures of the pump inlet medium during the process should be shown.
5. Suck Pump NPSH NPSHa: Effective NPSH.
6. Operating state: The operating state is divided into two types, continuous operation and intermittent operation.

B. Number and Power of Suck Pumps

The optimal number of pump stations for large and medium-sized suck pumps generally ranges from 4 to 8. For small and medium-sized stations, 3-6 units are suitable, while 2-3 units suffice for smaller stations.

Typically, a single pump machine suffices for normal operation. This is because one large suck pump performs equivalently to two smaller ones operating in parallel, considering the same lift and flow. Large pumps demonstrate higher efficiency compared to smaller ones, favoring energy conservation. However, under specific circumstances, employing two pumps in parallel may be warranted:

1. In cases of exceptionally high flow rates where one pump cannot meet demand.
2. For large suck pumps requiring a 50% standby rate, employing two smaller pumps for operation and two as standby (three in total) is advisable.
3. Some large suck pumps may be suitable for parallel operation without backup pumps, provided they fulfill 70% of the flow requirements. This ensures continued production even when one pump undergoes maintenance.
4. Suck pumps necessitating continuous 24-hour operation should have three sets available: one for operation, one for standby, and one for maintenance.

C. Suction Pump Type Selection

The selection of a suction pump model should align with the process parameters of the device, the physical and chemical properties of the conveyed medium, the operating cycle, and the structural characteristics of the suction pump. Centrifugal pumps, due to their simple structure, smooth liquid conveyance without pulsation, and ease of flow adjustment, are generally preferred, except in the following scenarios:

1. Metering Requirement: Choose a metering pump when precise metering is necessary.
2. High Lift and Low Flow: In instances where lift requirements are exceptionally high and flow rates are minimal, and no suitable small flow, high lift centrifugal pump is available, consider a reciprocating pump. If cavitation requirements are not stringent, a vortex pump may also suffice.
3. Low Head and High Flow: Opt for axial flow pumps or mixed flow pumps when facing low head and high flow conditions.
4. High Medium Viscosity: For fluids with high viscosity (>650～1000mm2/s), rotary lobe pumps such as screw pumps or reciprocating pumps are suitable. In cases of extremely high viscosity, specially designed high-viscosity screw pumps or reciprocating pumps can be employed.
5. Medium Air Content: If the medium contains more than 5% air, and the flow rate is low with viscosity less than 37.4mm2/s, a vortex pump can be considered. Alternatively, if pulsating flow is acceptable, a reciprocating pump may be used.
6. Self-Priming Requirement: For applications requiring frequent startup or where pump filling is inconvenient, opt for a suction pump with self-priming capabilities, such as a self-priming centrifugal pump, self-priming vortex pump, or self-priming positive displacement pump.

D. Selection of Suction Pump Series and Materials

The selection of suction pump series involves pumps with identical structure and purpose manufactured by the pump factory, such as the IS type clean water pump, Y type oil pump, ZA type chemical process pump, SJA type chemical process pump, among others. Once the suction pump type is established, the pump series and materials can be chosen based on process parameters and medium characteristics.

If a centrifugal pump is chosen, the following considerations may be taken into account:

1. Characteristic Pump Selection: Depending on the medium’s properties, opt for a suitable pump type such as a clean water pump, corrosion-resistant pump, chemical process pump, or impurity pump. For highly toxic, valuable, or radioactive substances intolerant to leakage, consider a leak-free pump (e.g., canned pump, magnetic pump) or a double-end mechanical seal equipped with a leak collection and alarm device. Volatile liquids like liquefied hydrocarbons may require a low NPSH pump, such as a barrel pump.
2. Installation Conditions: Choose between horizontal and vertical pumps (including submerged and pipeline pumps) based on site installation conditions.
3. Flow Rate: Select a single-suction pump, double-suction pump, or small flow centrifugal pump based on the required flow rate.
4. Lift: Opt for a single-stage pump, multi-stage pump, or high-speed centrifugal pump depending on the lift requirements.

Once these considerations are made, the appropriate suction pump series and manufacturer can be selected based on the characteristics of different pump series and the manufacturer’s conditions.

E. Determining the Suction Pump Model

Once the type, series, and material of the suction pump are chosen, the pump model can be determined based on samples and relevant information provided by the pump manufacturer.

1. Determining Positive Displacement Pump Model

• Determine Rated Flow and Rated Outlet Pressure: The rated flow (Q) typically uses the maximum flow directly. If this value is unavailable, use 1.1 to 1.5 times the normal flow. The rated outlet pressure (P) refers to the maximum pressure at the pump outlet.
• Check Flow Rate and Pressure: Compare the flow rate (Q) and pressure (P) provided by the positive displacement pump sample or technical data. Ensure that the chosen pump model can deliver the required flow rate and pressure for the process.
• Selection Criteria: Choose a pump model where the flow rate (Q) is less than or equal to the provided value [Q], and the pressure (P) is less than or equal to the provided value [P]. Additionally, ensure that the Net Positive Suction Head Required (NPSHr) of the pump is less than the available Net Positive Suction Head (NPSHa) of the device, with a safety margin (S) included.
• Comprehensive Selection: If multiple pump models meet the above criteria, prioritize the pump with high efficiency, low cost, and high reliability.

2. Determining Centrifugal Pump Model

• Determine Rated Flow and Head: Similar to positive displacement pumps, the rated flow and head are typically taken as the maximum values. If these values are unavailable, use 1.1 to 1.5 times the normal flow for flow and 1.05 to 1.1 times the required lift for head. For mediums with viscosity > 20mm2/s or containing solid particles, convert to rated flow and head for conveying clean water.
• Check Series Atlas: Based on the rated flow and head, identify one or more potential pump models from the series atlas.
• Performance Curve Check: Ensure that the rated operating point of the pump falls within the efficient pump working area on the performance curve. Also, verify that the NPSHa – necessary NPSHr requirement is met.
• Final Selection: If multiple pump specifications meet the criteria, choose the model with the highest comprehensive index, considering parameters such as efficiency, weight, and price.

F. Determining Prime Mover Power

1. Calculation of Shaft Power (Pa) of the Suction Pump

For Vane Pump: 𝑃𝑎=𝑄⋅𝐻⋅𝜌⋅𝑔𝜂Pa​=ηQ⋅H⋅ρ⋅g​

For Positive Displacement Pump: 𝑃𝑎=𝑄⋅𝑃𝑑⋅106𝜂⋅𝜂𝑡Pa​=η⋅ηt​Q⋅Pd​⋅106​

2. Determining Prime Mover Power

Select a prime mover with a power (kw) that matches the calculated shaft power (Pa).

3. Selection Criteria for Prime Mover

Consider factors such as explosion area, explosion-proof level, power supply, and gas supply conditions when choosing a suitable prime mover.

Where:

• $H$ = rated head of the pump (m)
• $Q$ = rated flow of the suction pump (m3/s)
• $\rho$ = medium density (kg/m3)
• $g$ = acceleration due to gravity (9.81 m/s2)
• $\eta$ = efficiency of the suction pump under rated conditions
• 𝑃𝑎Pa​ = shaft power under rated conditions of the suction pump (kw)
• 𝑃𝑑Pd​ = suction pump outlet pressure (MPa)
• 𝜂𝑡ηt​ = suction pump transmission device efficiency
• $K$ = efficiency margin coefficient of the prime mover

G. Determining Shaft Seal Type

The shaft seal is vital for preventing leakage between the suction pump shaft and the casing. Common types include packing seals, mechanical seals, and dynamic seals.

1. Packing Seal: Simple, inexpensive, and easy to maintain, but prone to leakage and power loss. Suitable for general media like water but not recommended for corrosive or hazardous substances.
2. Mechanical Seal: Offers excellent sealing, minimal leakage, and long lifespan but comes at a higher cost with stricter processing and maintenance requirements. Ideal for transporting petroleum and chemical media, including those with varying viscosities and containing particles.
3. Dynamic Seal: Utilizes centrifugal force to reduce medium pressure, preventing leaks during operation. Divided into back vane seals and auxiliary impeller seals, it’s reliable, affordable, and easy to maintain. Suitable for media with solid particles, but may incur higher power loss and shorter seal life compared to mechanical seals.

Packing seals are often paired with dynamic seals for parking purposes. Dynamic sealing is beneficial for media containing solid particles but may have drawbacks like increased power loss and shorter seal life compared to mechanical seals.

H. Coupling and Its Selection

Flexible couplings are commonly employed as pump couplings, serving to transmit power, accommodate relative displacement between the pump shaft and motor shaft, mitigate precise alignment requirements during coupling installation, dampen impact, and alter the natural vibration frequency of the shaft system to prevent hazardous vibrations.

Various types of couplings are utilized for sand pumps, including claw type elastic couplings, elastic pin couplings, diaphragm couplings, and hydraulic couplings.

1. Claw Type Elastic Coupling: Also referred to as an elastic block coupling, this type features a compact size, lightweight, simple structure, easy installation, and affordability, making it suitable for low-power and less critical applications.
2. Elastic Pin Coupling: This type of coupling connects two halves of coupling flanges with a pin. One end of the pin is fixedly assembled with the tapered pin hole on the flange of the half coupling using a conical surface and nut, while the other end features an elastic sleeve made of rubber, fitting into the stud hole pin of the other half coupling flange. Elastic pin couplings are known for their simple structure, convenient installation, easy replacement, compact size, lightweight, and high transmission torque, making them widely used in various rotary pumps.
3. Diaphragm Coupling: Consisting of a group of thin metal spring plates shaped into various forms and connected with bolts to the two halves of the coupling, diaphragm couplings offer a simple structure, require no lubrication or maintenance, exhibit high temperature resistance, good anti-misalignment performance, high reliability, and large transmission torque. However, they are relatively expensive. The JM1J type integral diaphragm coupling connected to the intermediate shaft is recommended by the water pump industry.
4. Hydraulic Coupling: Also known as a hydraulic transmission device, the hydraulic coupling comprises three main parts: the shell, pump wheel, and turbine. During operation, the kinetic energy of the motor is transmitted to the hydraulic oil through the pump wheel, which then transfers the kinetic energy to the turbine output through circulating flow. Hydraulic couplings offer smooth starts, overload protection, and stepless speed regulation. However, they incur certain power losses and are relatively expensive, making them suitable for large sand pumps with high power or frequent changes in working conditions.

I. Water Pump Selection

1. Selection Principle

• Meet Process Parameters: Consider parameters such as flow, head, temperature, pressure, and Net Positive Suction Head (NPSH) required for the process.
• Suitability for Transported Liquid: Ensure that the pump can handle corrosive liquids, liquids intolerant of leakage, those containing long fibers, high-temperature or high-pressure liquids, and viscous liquids.
• Environmental Conditions: Pay attention to installation location, environmental conditions, power grid conditions, and hazardous area classification on-site.

2. Use Different Pump Types: Select water pump types based on environmental conditions and process requirements.

3. Determination of Water Pump Flow: Identify the rated, minimum, and maximum flow of the water pump based on process requirements, with the maximum flow rate serving as the selection basis. If the maximum flow rate is unspecified, use 1.1 times the rated flow as a reference.

4. Determination of Water Pump Head: The total head includes actual head and loss head. Actual head is measured on-site, while loss head is determined by:

• Selecting pump diameter and inlet/outlet pipe diameter based on required flow rate.
• Choosing pump model from performance table based on required flow and head. Typically, the rated head is 1.05 to 1.1 times the head required by the water pump device.

5. Model Selection:

• Refer to the performance specification table provided by the manufacturer.
• Compare designed flow and head values with those in the table, aiming for consistency or proximity to the middle row, which represents the high-efficiency working area.
• Use the model selection table to find the intersecting point of design flow and head values, then compare and analyze multiple suitable models for technical and economic viability.

6. Pipeline Arrangement: After primary selection, determine specific pipeline arrangements based on the selected pump. Ensure that the pump’s working point falls within its high-efficiency area.

7. Check Working Range: Confirm that the maximum and minimum design heads do not exceed the pump’s working range.

About OCEAN Pump

In this article, we’ve touched on the essential considerations for selecting and configuring sand suction pump units and their supporting water pump counterparts. If you have any insights or ideas to share on this topic, we welcome your input. Should you have specific requirements in your operational settings, don’t hesitate to reach out to us for further assistance and to obtain more detailed configuration parameters.

Tai’an Ocean Pump (OCEAN Pump) Co., Ltd. stands at the forefront as the premier manufacturer, supplier, and exporter of sand pumps and sand dredger solutions in China. With a team of over 30 skilled experts in sand pump machinery and a sprawling 15,000 square meters factory, we boast a diverse range of products. Our lineup includes over 20 types of sand pumps, slurry pumps, sand dredgers, and related components, meticulously crafted to meet your pumping needs. Recognized by the government as a Certification of New Hi-tech Enterprises, OCEAN Pump is committed to delivering cutting-edge solutions to our customers.

We offer comprehensive sand, slurry, and gravel pumping solutions, along with all the necessary components. Our portfolio encompasses centrifugal portable sand pumps, marine sand pumps, suction dredge pumps, gravel pumps, mud pumps, submersible slurry pumps, vertical sand pumps, compact sand pump dredgers, submersible dredgers, and much more. Whether it’s mining, metallurgy, coal washing, power plants, or sewage water treatment, our products find application in a diverse array of industries. Furthermore, we extend our reach to pump dealers worldwide, inviting partnerships for mutual growth and success.