Jiangsu Haifa Machinery Manufacturing Co., Ltd.

In chemical plants, oil refineries, and low-temperature medium transfer systems, we often encounter a tricky working condition: the effective Net Positive Suction Head available (NPSHa) at the customer is too low, and even before the pump officially runs, insufficient suction conditions are already exposed during the selection phase. On the surface, this issue appears to be "difficult to select a pump," but in reality, it stems from a mismatch between the plant conditions, medium characteristics, inlet pressure, liquid level height, pipeline resistance, and pump structure. For ordinary horizontal centrifugal pumps, if the on-site NPSHa is low, it can easily lead to cavitation, vibration, noise, flow fluctuations, and in severe cases, cavitation damage to the impeller, abnormal bearing forces, and mechanical seal failure. Not long ago, our, Jiangsu Haifa Machinery Manufacturing Co., Ltd., encountered a similar issue in a customer project. The customer initially considered using an ordinary horizontal chemical process pump, but after our technical staff reviewed the situation, we found that the on suction conditions were tight the inlet pipeline resistance was high, and the plant liquid level could not be significantly raised. we proceeded with the ordinary horizontal pump plan, the operational risks would be high in the later stages. The on-site parameters were: Q: 180m³/h, H: 225m, propane specific gravity: 0.505kg/m³, temperature: -58°C, NPSHa: 1m. After recalculating and comparing structures, we ultimately the API610-VS6-HVS vertical multistage barrel pump, i.e., the VSD/VDD vertical multistage barrel pump solution. The core purpose of this solution is clear: by using a vertical barrel structure, the first-stage impeller is placed at a lower position, leveraging the liquid column pressure inside the barrel to improve the pump inlet conditions, structurally reducing the risk of cavitation This solution was successfully implemented in the customer's plant, solving the trouble of modifying the process design and on-site pipeline changes.

1. Why does low NPSHa occur at customer sites?

In pump selection, NPSH is not a parameter that can be overlooked. Many customers focus on providing flow rate, head, temperature, pressure, and materials during inquiries, but pay insufficient attention to NPSHa. In reality, for easily vaporizing media, low-temperature media, light hydrocarbons, liquefied gas, condensate, methanol, ammonia water, and chemical media containing volatile components, NPSH is often more critical than head. Low NPSHa at customer sites typically has several causes: First, low liquid level in the storage tank, resulting in insufficient static pressure at the pump inlet. Second, high saturation vapor pressure of the medium, making it prone to vaporization with slight pressure drops. Third, long suction pipelines with many elbows, valves, and filters, leading to high inlet resistance losses. Fourth, the plant is already built, and the pump foundation and nozzle elevations cannot be easily adjusted. Fifth, the original design uses a horizontal pump with a high pump centerline, causing insufficient inlet pressure at the first-stage impeller. When reviewing the customer's data sheet, we focused on verifying the inlet pressure, medium temperature, saturation vapor pressure, inlet pipeline losses, pump installation elevation, and NPSHa. The results showed that if an ordinary horizontal chemical process pump were still used, significant adjustments to the plant pipelines and foundation would be required; otherwise, long-term pump operation would be unstable. In such cases, rather than forcing a reduction in the pump's required NPSHr, it is better to reconsider the pump structure. The vertical multistage barrel pump is a more suitable solution for such low NPSH conditions.

1. Why is the verticalistage barrel pump suitable for low NPSH conditions?

Jiangsu Ha's API610 vertical multage barrel pump features a vertical installation, suction, and multistage impeller pressurization structure. Compared to ordinary horizontal pumps, its greatest advantage is not simply "small footprint," but the ability to improve the pump's suction conditions. The impeller inlet position of an ordinary horizontal pump is largely limited by the pump foundation height. If the on-site liquid level is low and the inlet pressure is insufficient the pump can easily approach the cavitation boundary. contrast, the first-stage impeller of vertical barrel pump can placed at a lower position inside the barrel. After the liquid enters the barrel, a stable suction environment is formed, providing better priming conditions for the pump's first-stage imp. Our understanding is simple: for low NPSH conditions, it's not just about whether the pump can deliver flow and head, but more importantly, whether it can stably draw in the medium over the long term. The barrel structure of the vertical multistage barrel pump essentially creates a more stable suction space for the pump, reducing inlet turbulence and pressure fluctuations at the suction stage, and lowering NPSHr through well-designed first-stage impeller. For customers with limited liquid levels, low inlet pressure, and easily vaporizing media, the vertical barrel pump is more reliable than an ordinary horizontal pump.

1. What technical adjustments did we make for the customer?

This project was not simply about replacing a horizontal pump with a vertical one. During our internal review, we made several key adjustments.

1. First-stage impeller designed for low NPSH performance: Under low NPSH conditions, the first impeller is critical. During selection, we did not solely pursue high efficiency points but instead considered the first-stage impeller's inlet flow velocity, blade inlet angle, suction area, and the pump's NPSHr together. For multistage barrel pumps, the subsequent stages primarily handle pressurization, while first-stage impeller must prioritize suction performance. Only with stable first-stage suction can the subsequent multistage impellers smoothly build up head.

2. structure to reduce inlet cavitation risk: The customer could not significantly raise the storage tank liquid level or rearrange the pump foundation. By adopting the vertical barrel structure, placed the key suction components at the lower part of the barrel giving the pump more favorable pressure conditions. This is the typical value of the API610 vertical multistage barrel pump in low NPSH conditions it doesn't force customers to make major plant modifications but helps the plant adapt to on-site conditions through pump structure.

3 Multistage impellers to meet high head requirements: The customer not only had low NPSH but also required a certain discharge pressure. Even if a single-stage pump could solve the suction issue, it would struggle to meet the high head requirement. By using a multistage, we could configure stages for gradual pressurization, allowing the pump to meet the plant's discharge pressure requirements even under low suction conditions. This type of vertical multistage barrel pump is suitable for applications in oil refining, coal chemical, fine chemical, low-temperature engineering, light hydrocarbon transfer, condensate recovery, liquefied gas plants, aromatics plants, methanol plants, and ammonia medium transfer.   4 Material selection based on medium corrosiveness and temperature conditions: Jiangsu Haifa has a solid manufacturing foundation in corrosion-resistant materials. Depending on the medium, we can select materials such as 304,304L, 316, 316L, 2205 duplex stainless steel, titanium alloy, Hastelloy, Monel, 904, 825, Mo2Ti, etc. Low NPSH conditions often involve volatile or special chemical media, so material selection cannot be solely on price. We typically determine the material for flow-wetted parts by considering the medium composition, water content, chloride ion content, temperature, pressure, and erosion conditions to avoid corrosion, pitting, or erosion wear during pump operation.

4 Technical parameters of Jiangsu Haifa's API610 chemical process pumps  
Jiangsu Haifa Machinery Manufacturing Co., Ltd. manufactures chemical process pumps in accordance with the API610 standard, covering various structural forms such as OH, BB, and VS, and can perform selection design and manufacturing based on customer working conditions.  
Project Technical Content  
Execution Standard: API610 Standard for Centrifugal Pumps for Petroleum, Petrochemical, and Natural Gas Industries  
Product Series: OH1, OH2, OH3, BB1~BB5, VS1~VS6  
Vertical Barrel Pump Series: VSDDD Vertical Multistage Barrel Pump  
Structural Form: Vertical installation barrel suction, multistage impellers, radial or mixed-flow first-stage impeller configuration  
Applicable Conditions: Low NPSH, high head, low liquid level, easily vaporizing media, high-pressure transfer  
Typical Media: Condensate, liquefied hydrocarbons, methanol, ammonia water, light oil,atics, low-temperature media, corrosive chemical liquids  
Common Materials: 304, 304L, 316, 316L, 2205 duplex stainless steel, titanium alloy, Hastelloy, Monel,904, 825, Mo2Ti, etc.  
Shaft Seal Configuration: Can be configured per API682 mechanical seal and flush plans  
Testing Capabilities: Furnace analysis, spectral analysis, dye penetrant inspection, X-ray inspection, high-temperature metallography  
Selection Parameters: Flow rate 180m³/h, head 225m, inlet pressure 0.055MPa, discharge pressure 1.3MPa, NPSHa 1m, medium temperature -58°C, density 0.505kg/m³, viscosity 0.098, corrosiveness, installation elevation, etc., determined per project data sheet  
In actual quotations and technical agreements, we further determine the pump's flow rate, head, number of stages, barrel length, impeller diameter, flange standards, seal plans, motor power, material grades, and cooling/flush plans based the customer's data sheet. For low NPSH conditions, special attention must be paid to verifying the safety margin between NPSHa and NPSHr.

1. Practical value of the vertical multistage barrel for the customer

After project ultimately adopted the vertical multistage barrel pump, the customer's key concerns were addressed. First, the pump's suction conditions became more stable. The barrel structure improved the first-stage impeller inlet condition, reducing the probability of cavitation Second, the amount of plant modification was reduced. The customer did not need to significantly raise the storage tank liquid level or make extensive adjustments to the pump foundation and pipeline elevations. Third, pump could simultaneously meet low NPSH and high head requirements. The multistage impellers provided gradual pressurization, making it more suitable for high discharge pressure conditions than single-stage pump. Fourth, operational reliability was higher. With reduced cavitation risk, the risks of pump vibration, noise, impeller damage, bearing stress, and seal failure all decreased. Fifth, maintenance was better assured. During the design phase, we considered materials, seals, inspection, and manufacturing processes together, rather than simply building a pump that "just runs" based on price.

1. Our recommendations for pump selection under low NPSH conditions

Based on our experience with API610 chemical process pumps, low NPSH conditions cannot be handled solely by empirical judgment, nor can horizontal pump parameters be simply. Especially for easily vaporizing media, high-temperature media, low-temperature media, and plants with low inlet pressure, the cavitation issue must be thoroughly calculated upfront. We recommend that customers provide the following information as comprehensively as possible during inquiries: medium name, medium composition, temperature, density, viscosity, saturation vapor pressure, flow rate, head, inlet pressure, discharge pressure, NPSHa, storage tank liquid level, pump installation elevation, suction pipeline length, valve and filter configuration, material requirements, explosion-proof class, and-site continuous operation requirements. The more complete the data, the more accurate the pump recommendation. If customers only provide flow rate head, we can still perform preliminary selection, but for low NPSH conditions, this is insufficient. Truly reliable selection must both the plant suction conditions and the pump structure.

1. Conclusion

Jiangsu Haifa Machinery Manufacturing Co Ltd. does not just manufacture API610 chemical process pumps according to drawings; more importantly, we help customers solve on-site problems. Low NPSH conditions may seem like just a parameter deficiency, but they affect whether the pump can operate stably and whether the plant can achieve long-term production. In this project, our core approach in recommending the vertical multistage barrel pump was to use the right pump type to address the insufficient on-site suction conditions. For conditions such as low liquid level, low inlet pressure, easily vaporizing media, and high head transfer, the API610 VSD/VDD vertical multistage barrel pump is a more reliable choice. In the future, if customers encounter issues such as low NPSH, pump cavitation, insufficient inlet conditions, or ordinary horizontal pumps failing to meet NPSH requirements in oil refining, chemical, coal chemical, fine chemical, low-temperature engineering, and liquefied gas transfer projects, they can provide us with their on-site data sheets. We will review the medium, working conditions, structure, materials, seals, and manufacturing inspection together to provide a more suitable API610 chemical process pump solution for long-term on-site operation.

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