Selection Principles of Pumps for Sale

1. Pump Selection Principles

1. The type and performance of the selected pumps meet the process parameters requirements such as flow, head, pressure, temperature, cavitation flow, suction depth, etc.
2. Meet the requirements of media characteristics. For pump that transports flammable, explosive, toxic or precious media, reliable shaft seals or non-leakage pumps are required, such as magnetic drive pumps, diaphragm pumps, and canned pumps. For pump that transports corrosive media, the flow parts are required to use corrosion-resistant materials, such as AFB stainless steel corrosion-resistant pumps, and CQF engineering plastic magnetic drive pumps. For pump that transports solid particles, the flow parts are required to be made of wear-resistant materials, and the shaft seal should be flushed with clean liquid when necessary.
3. High mechanical reliability, low noise and low vibration.
4. Economically, the total cost of pumps for sale costs, operating costs, maintenance costs, and management costs should be taken into account as the lowest.
5. The centrifugal pumps for sale has the characteristics of high speed, small size, light weight, high efficiency, large flow, simple structure, no pulsation when medium transportation, stable performance, easy operation and convenient maintenance.

1.1 Therefore, in addition to the following conditions, it is better to select centrifugal pumps for sale.

1. Choose a metering pump when there is a metering requirement.
2. When it requires high head, small flow and no suitable small flow high head centrifugal pumps for sales can be used, selecting reciprocating pumps. If cavitation requirements are not high, vortex pumps can also be used.
3. When the head is very low and the flow is large, choosing axial flow pump and mixed flow pump.
4. When the medium viscosity is large (greater than 650~1000mm2/s), considering the rotor pump or reciprocating pump (gear pump, screw pump).
5. When the air content of the medium is 75%, the flow rate is small and the viscosity is less than 37.4mm2/s, the vortex pump can be used.
6. If the pump equipment needs to be started frequently, or it is inconvenient to fill the pump with water, a self-priming pump should be selected, such as a self-priming centrifugal pump, a self-priming vortex pump, and a pneumatic (electric) diaphragm pump.

2. Selection Basis

The selection basis of pumps for sale should be considered from five aspects according to the process and water supply and drainage requirements, including liquid delivery volume, pump device head, liquid properties, piping layout, and operating conditions, etc.

1. Flow rate is one of the important performance data of pumps for sale selection, it is directly related to the production capacity and conveying capacity of the entire pump device. For example, in the process design of the design institute, the normal, minimum and maximum flow rates of the pump for sale can be calculated. When selecting the pump for sale, take the maximum flow rate as the basis and take into account the normal flow rate. When there is no maximum flow rate, usually 1.1 times the normal flow rate can be taken as the maximum flow rate.
2. The head is another important performance data for pump selection. Generally speaking, the head of the pump for sale should have a margin of 5%-10%.
3. Liquid properties, including the liquid medium name, physical properties, chemical properties and other properties. The physical properties include temperature c, density d, viscosity u, solid particle diameter and gas content in the medium, etc. This relates to the head, the calculation of effective cavitation allowance and the suitable pumps for sale. The chemical properties mainly refer to the chemical corrosiveness and toxicity of the liquid medium, which is an important basis for selecting the pump material and the shaft seal type.
4. The pipeline layout conditions of the pumps for sale refer to the data such as liquid delivery height, delivery distance and the delivery direction, the lowest liquid level on the suction side, the highest liquid level on the discharge side, pipe specifications and length, materials, pipe fitting specifications, quantity, etc. to carry out pump for sale head calculation and cavitation margin check.
5. There are many operating conditions, such as liquid operation T, saturated steam power P, suction side pressure PS (absolute), discharge side container pressure PZ, altitude, whether the ambient temperature operation is intermittent or continuous, whether the pump position is fixed or removable.

Basic composition of water pump: Motor, coupling, pump head (body) and frame (horizontal)

2.1 The main parameters of the water pump are as follows.

1. Flow, represented by Q, the unit is M³/H, L/S.
2. Head, represented by H, the unit is M.
3. For clean water pumps, the parameter of required NPSH (M) is very important, especially when it is used for water suction supply equipment.
4. For submersible pumps, the parameter of rated current (A) is very important, especially when used in variable frequency water supply equipment.

The main parameters of the motor: motor power (KW), rotation speed (r/min), rated voltage (V), rated current (A).

3. What is the efficiency of the pumps? What is the formula?

The efficiency of the pumps for sale refers to the ratio of the effective power to the shaft power. The formula is η=Pe/P.

The pumps for sale power usually refers to the input power, that is, the power transmitted from the prime mover to the pump shaft, so it is also called shaft power, denoted by P.

Effective power of pumps for sale is: the product of pump lift, mass flow and gravitational acceleration.

Pe=ρg QH (W) or Pe=γQH/1000（KW）

ρ: Density of the liquid delivered by the pump(kg/m³).

γ: The gravity of the liquid delivered by the pumps. γ=ρg (N/ m3)

g: acceleration due to gravity (m/s).

Mass flow Qm=ρQ (t/h or kg/s).

4. What is cavitation margin? What is suction lift? What is the letter of the respective measurement unit?

When the pumps for sale is working, the liquid will generate vapor at the inlet of the impeller due to a certain vacuum pressure. The vaporized bubbles will erode the impeller and other metal surfaces under the impact movement of the liquid mass point, thereby destroying the impeller and other metals. At this time, the vacuum pressure is called Vaporization pressure. The cavitation margin refers to the excess energy of unit weight liquid exceeding the vaporization pressure at the pump suction port，the unit is meters, denoted by (NPSH)r. The suction lift is the necessary NPSH Δh: the vacuum degree that the pumps for sale allows to extract the liquid, that is, the allowable installation height of the pumps for sale, in meters.

Suction lift = standard atmospheric pressure (10.33 meters) – NPSH – safe amount (0.5 meters)

The vacuum height of the pipeline under standard atmospheric pressure is 10.33 meters.

For example: a pump for sale necessary NPSH is 4.0 meters, what is the suction lift Δh?

Δh=10.33-4.0-0.5=5.83m

5. What is the characteristic curve of the pumps for sale? Which elements are included? How does it work?

The curve representing the relationship between the main performance parameters is usually called the performance curve or characteristic curve of the centrifugal pumps for sale. In essence, the performance curve of a centrifugal pump is the external manifestation of the liquid movement law in the pumps for sale, which is obtained through actual measurement. The characteristic curves include: flow-head curve (Q-H), flow-efficiency curve (Q-η), flow-power curve (Q-N), flow-NPSH curve (Q-(NPSH)r). The function of the performance curve is that at any flow point of the pumps for sale, a set of relative head, power, efficiency and NPSH values can be found on the curve. This set of parameters is called working state, referred to as working condition or working condition point. The working condition at the highest efficiency point of the centrifugal pumps for sale is called the optimum working condition point, and the optimum working condition point is generally the designed working condition point. Generally, the rated parameters of the centrifugal pumps for sale, that is, the designed working condition point and the optimal working condition point coincide or are very close. In actual work, the pumps should run in the efficiency range, where the pumps not only save energy, but also ensure the normal working. Therefore, it is very important to understand the performance parameters of the pumps for sale.

6. General Procedure for pumps for sale Selection

A. According to the layout of the pumps for sale, terrain conditions, water level conditions, operating conditions, economic plans and other factors.

B. Consider choosing horizontal, vertical and other types (pipeline, right-angle, variable-angle, corner, parallel, vertical, submersible, detachable, submerged, non-clogging, self-priming type, gear type, oil-filled type, water-filled type). Horizontal pumps for sale are easy to disassemble and assemble, easy to manage, but they are bulky, expensive, and require a lot of floor space. Vertical pumps: In many cases the impeller is submerged in water, can be started at any time, easy to automatic or remote control, and compact, small installation area, less expensive.

C. According to the nature of the liquid medium, determine the clean water pump, hot water pump, oil pump, chemical pump or corrosion-resistant pump or impurity pump, or use a non-blocking pump. pumps for sale installed in explosive areas should use explosion-proof motors according to the explosive area level.

D. Consider pneumatic or electric according to the vibration form (electric is divided into 220v voltage and 380v voltage).

E. According to the flow rate, determine whether the single-suction pumps for saleor the double-suction pumps for sale. According to the lift, choose a single-suction pump or a multi-suction pump, a high-speed pump or a low-speed pump (air conditioning pump), and the efficiency of a multi-stage pump is lower than a single-stage pump. When both single-stage pump and multi-stage pump can be used, single-stage pump is a better choice.

F. Determine the specific model of the pumps for sale. After determining which series of pumps for sale to use, select specific model on the type spectrum or series characteristic curve according to the maximum flow rate and lift which is from amplifying 5% to 10% margin of the maximum flow.

Using the pumps characteristic curve, find the required flow value on the abscissa and the required head value on the ordinate, draw a vertical line upword and a horizontal line to the right respectively, and the intersection of the two lines falls on the characteristic curve, this is the suitable types of pumps for sale. But this ideal situation is generally rare, and the following situations are usually encountered as follows.

1. The intersection point is above the characteristic curve, which means that the flow meets the requirements, but the head is not enough. At this time, if the head is similar to the ideal condition, or the difference is about 5%, it can still be used. If the head is very different, choose a pump with a larger head. Or try to reduce the pipeline resistance loss.
2. The intersection point is below the characteristic curve, and within the fan-shaped trapezoid range of the pump characteristic curve, this ideal model can be used. If the head is very different, according to the required Q, H, its ns and cutting formula, cut the impeller diameter. If the intersection point does not fall within the range of the fan-shaped trapezoid, the pumps for sale with a smaller head should be selected.

When choosing the pumps for sale, sometimes it is necessary to consider the production process requirements, and choose Q-H characteristic curves of different shapes.

G. After the model is determined, for the water pump or the pump which transports medium similar to water on physical and chemical, it is necessary to correct according to the performance table or performance curve on the relevant product catalog to see whether the normal operating point is in the pump priority work area. Whether the effective NPSH is greater than (NPSH). It can also be reversed to correct the geometric installation height according to NPSH.

H. For liquid pumps that transports medium with a viscosity greater than 20mm2/s, it is necessary to convert the pump characteristic curve in the experimental state of clean water into the performance curve of the corresponding viscosity state, especially the suction performance should be carefully calculated or checked.

I. Determine the pumps quantity and spare rates.

Generally, one set of pumps for sale is used for working. Because one large pump is equivalent to two small pumps working in parallel (meaning the same lift and flow), the efficiency of the large pump is higher than that of the small pump, so from the perspective of energy saving, it is better to choose one large pump instead of two small pumps. But two pumps can be considered for parallel cooperation  in the following situations.

1. The flow is very large, a pump cannot reach this flow.
2. For large pumps that need a 50% spare rate, two smaller pumps can be used, and the other two sets are standby.
3. For some large pumps, the pumps with 70% flow requirements can be selected for parallel operation, and no spare pump is needed. When one pump is overhauled, the other pump still undertakes 70% of the production.
4. For pumps that need to run continuously for 24 hours, three pumps should be spared, one for normal work, one for standby and one for maintenance.

7. Conclusion

When choosing a pump to purchase, there are some key selection principles to follow to ensure that the selected pump will meet specific requirements and achieve the best results in terms of performance and economics. The following are conclusive principles for pump purchase:

1. Consider process parameters: The selected pump should meet the requirements of process parameters such as flow, head, pressure, temperature, cavitation flow, and suction depth. Ensuring that the type and performance of the selected pump meet these parameters is key to efficient and effective operation.
2. Consider the characteristics of the medium: When the pump handles flammable, explosive, toxic or valuable media, it needs a reliable shaft seal mechanism or a leak-free pump, such as a magnetic drive pump, a diaphragm pump and a sealed pump. For pumps that handle corrosive media, it is necessary to use flow parts made of corrosion-resistant materials, such as AFB stainless steel corrosion-resistant pumps and CQF engineering plastic magnetic pumps. For pumps transporting solid particles, it is necessary to use flow parts made of wear-resistant materials and flush the shaft seal with cleaning liquid when necessary.
3. Go for mechanical reliability, low noise and low vibration: Choose a pump with high mechanical reliability to ensure continuous operation. Consider selecting a pump with lower noise and vibration levels to reduce environmental disturbance and increase workplace safety.
4. Economic considerations: comprehensively consider purchase cost, operating cost, maintenance cost and management cost, etc., and pursue the lowest total pump cost. Consider factors such as energy efficiency, ease of maintenance and durability to achieve economic benefits while maintaining required performance and reliability.

In summary, by following these pump purchasing principles, you can ensure that the pump you select meets your application requirements, performs well, and operates efficiently and reliably at the lowest cost throughout its lifetime. Therefore, when making a pump purchase, various factors should be carefully evaluated and compared and the pump best suited for a specific application should be selected. If you have any questions, you can contact us.

OCEAN PUMP has engaged in the development, production and sales of sand pump machine such as sand suction pumps, dredge pumps, mud pumps, slurry pumps, submersible pumps, gravel pumps, portable sand pumps, sand dredgers for more than 20 years. Through in-depth exchanges, OCEAN PUMP is familiar with the construction conditions and requirements of various countries in the world. OCEAN PUMP not only provides high-quality dredging equipment and industry solutions, but also provides on-site installation services. Please feel free to contact us about program design and equipment problems in dredging, sand pumping, and relay.