What effect does temperature have on the selection of centrifugal pumps?

Temperature is one of the most important factors in pump selection. The operating temperature of the pump will affect the selection of pump materials, the selection of seals, the selection of lubrication methods, etc., so the temperature factor needs to be taken into consideration when selecting a pump.

First, there are two concepts to understand: temperature and absolute zero.

Temperature is the measure of the amount of heat present in a gas, liquid, or solid. The common temperature scales that everyone is familiar with are Fahrenheit and Celsius, two systems invented in the 1700s. The two systems differ in important ways:

1) The freezing point of water is 0 °C or 32 °F

2) The boiling point of water is 100 °C or 212 °F

Absolute zero is defined as the lowest possible temperature. This is the point at which the atoms in a substance are completely still and do not transfer any heat energy. Temperature measurements relative to absolute zero are expressed in Kelvins (K) in the Celsius system (0 K = -273.15 o C) and in Rankines (o R) in the Fahrenheit system (0 o R = 459.67 o F). Note that Kelvin is a "no degree" unit of measurement.

Secondly, you need to understand the relationship between temperature and pressure.

Temperature not only affects the stability and efficiency of pump operation, but also the pressure of the system. When the temperature of a gas approaches absolute zero, it becomes a liquid. As the temperature continues to rise, the pressure of the gas also increases. If the cryogenic fluid exceeds its boiling point, it will become a gas and create serious pressure and sealing problems.

Because different media form pressure in different ways, a system must be designed specifically for the characteristics of the pumped media. If this is not taken into account, failures may occur, costing the business a lot of time, money, and production.

In addition, pay special attention to the impact of the ambient temperature at the user's site.

When the pump is installed outdoors or permanently placed outdoors, and the temperature drops significantly at night, the liquid in the pump may freeze. When these pumps are restarted, problems may occur - damage or wear of parts. Therefore, an insulation jacket or integral insulation layer may be required to insulate or heat the pump. Alternatively, the pump can be mounted on a skid or trolley to allow the operator to move it indoors.

The expected temperature range that the pump needs to handle during operation is critical to making the right selection, involving not only the type and structure of the pump, but also the selection of pump components. Although temperature seems to be a familiar concept, in industrial applications it can make operation complicated or the equipment less reliable.

In the pump selection process, both the ambient temperature of the site and the temperature of the pumped medium must be considered.

Temperature affects centrifugal pumps in the following ways:

1. Effect on structural materials: If certain chemicals are being pumped, corrosion may occur depending on the temperature. Hot boiling liquids will have a greater corrosive effect on materials than cooler liquids. Therefore, it is important to check chemical compatibility at pumping temperatures. Extremely low temperatures (such as -150 o C and below) will make many materials brittle, such as standard carbon steel, so systems such as pumping LNG or other cryogenic liquids must use specialized component materials. By adding certain elements or forging metals with certain grain structures, it is possible to create parts that can withstand even these extreme conditions.
2. Pump components: For packing seals, as temperature increases, heat is transferred from the packing gland through the shaft to the bearings. This can lead to a significant reduction in bearing life and may even cause the bearings to seize.
3. Fluid viscosity: Liquids affected by temperature will change viscosity during pumping. For example, honey will become thinner when heated, changing the way it pumps. Therefore, understanding the effect of temperature changes on product viscosity during pumping will ensure the correct pump (type structure) is selected.
4. Part expansion: At high temperatures, metal parts will expand at different rates. This is particularly important during the pump selection process and will affect the structural materials you choose.
5. Insulation or keeping low temperature: In some cases, your application may need to maintain a certain temperature. This can be achieved by maintaining flow conditions or using insulation jackets/integral insulation.

Temperature affects:

1. Pump structure. For example, when the medium temperature exceeds 160 ℃, a pump with the pump foot as the centerline support is selected; when the medium temperature exceeds 200 ℃, a radial split structure pump is selected; when the medium temperature reaches about 400 ℃ and the pumping pressure is not too high, such as the bottom oil slurry pump in the petrochemical industry, in order to minimize possible leakage points, an OH2 pump is usually selected; when the medium temperature reaches about 400 ℃, although the pressure is not too high, but a single-stage pump or a two-stage pump cannot meet it (such as the radiation furnace feed pump in the petrochemical industry), in order to ensure safety, a BB5 pump is usually selected; when transporting low-temperature media, it is recommended to use a VS6 vertical barrel pump for easy cold preservation; when the medium viscosity is high or easy to solidify or crystallize at room temperature, it is necessary to configure an insulation jacket or heat/insulate the pump as a whole; when the viscosity is too high at the pumping temperature, it is usually not suitable to use a centrifugal pump.
2. Material selection. For example: when the pumping medium is below zero but not too low, low-temperature carbon steel or austenitic stainless steel is usually used; when the pumping medium is below zero and low, austenitic stainless steel is usually used; when the pumping medium is high-temperature oil slurry and contains catalyst particles, a liner OH2 pump is selected, and the liner and impeller are made of wear-resistant cast iron; when the pumping medium is high-temperature oil slurry and does not contain catalyst particles, a liner OH2 pump is selected, and the liner and impeller are made of CA-6NM material.
3. Selection of mechanical seals and systems. For example: under normal temperature conditions, type A seals are usually selected, and the maximum operating temperature can reach 176°C; under low temperature conditions, type B seals are usually selected, and the maximum operating temperature can reach 176°C; under high temperature conditions, type C seals are usually selected, and the maximum operating temperature can reach 400°C; pumps with operating temperatures greater than or equal to the auto-ignition point of the pumping medium usually choose layout 2 or 3; under high or low temperature conditions, it is usually necessary to add a PLAN62 seal flushing solution.