Working Principle, Characteristics and Applications of Chemical Pumps

What is a Chemical Pump

A pump is a machine used to convey liquids and increase their pressure. A chemical pump is a general term referring to pumps that meet the special requirements of chemical production, which include the following aspects:

Meeting the requirements of chemical processes

Withstanding high and low temperatures

Resisting corrosion

Withstanding wear and tear

Achieving zero or minimal leakage

Capable of conveying liquids in critical states

Ensuring reliable operation

These requirements are mainly aimed at the characteristics of the conveyed media. All pumps that can improve and enhance corrosion resistance against all chemicals except pure water through material selection or structural modification are collectively referred to as chemical pumps. They include:

Centrifugal pumps (conventional centrifugal pumps, axial-flow pumps, canned centrifugal pumps, magnetic centrifugal pumps, etc.)

Positive displacement pumps (gear pumps, screw pumps, plunger pumps, vane pumps, reciprocating pumps, etc.)

Other special pumps (pumps lined with metal-clad plastics or rubber materials)

Chemical pumps are energy-efficient pumps designed through a national collaborative program. Their performance and technical specifications are designed in accordance with the performance and dimensions specified in the international standard ISO 2858. Their advantages include: a rationally arranged hydraulic performance across the entire product series, a wide selection range for users, a back-opening structure for easy maintenance, and efficiency and suction lift reaching the international advanced level.

Characteristics and Applications of Chemical Pumps

Characteristics

Chemical pumps feature stable and reliable performance, excellent sealing properties, an aesthetically pleasing design, and convenient operation and maintenance. They play an important role in improving product quality, reducing run, emission, drip and leakage, preventing pollution, and improving the environment.

Applications

Chemical pumps are suitable for conveying corrosive media or media with special physical and chemical properties at various temperatures in industries such as chemical engineering, petroleum, metallurgy, power stations, food, pharmaceuticals, and synthetic fibers.

The main types of chemical pumps include: various glass fiber chemical pumps, corrosion-resistant plastic pumps, high-temperature chemical pumps, standard chemical pumps, magnetically driven pumps, insulated chemical pumps, and petrochemical pumps.

Chemical pumps are used for:

Pumping clean water, as well as media containing abrasive substances that are harmful to conventional pump body materials, suspended matter that is corrosive to stainless steel, and non-explosive substances

Water supply systems

Heating, air conditioning, cooling and circulation systems

Civil and industrial applications

Fire-fighting systems

Irrigation

Daily, civil, industrial and horticultural irrigation purposes

Rainwater harvesting projects

Occasions requiring low noise levels

Pipeline pressure boosting, suitable for conveying corrosive, explosive, particle-containing water or liquids

Working Principle of Chemical Pumps

Before starting the pump, the suction pipe and the pump body must be completely filled with liquid. Once the pump is started, the impeller rotates at high speed, and the liquid inside rotates along with the impeller blades. Under the action of centrifugal force, the liquid is thrown outwards from the impeller. The velocity of the discharged liquid gradually decreases in the diffuser chamber of the pump casing, while the pressure gradually increases, and then the liquid flows out through the pump outlet and discharge pipe.

At this time, a vacuum low-pressure zone (devoid of both air and liquid) is formed at the center of the impeller blades as the liquid is thrown to the periphery. The liquid in the sump flows into the pump through the suction pipe under the action of atmospheric pressure on the sump surface. In this way, liquid is continuously drawn from the sump and discharged through the outlet pipe.

Sealing Forms of Chemical Pumps

The main sealing forms of chemical pumps include: oil seal, gasket seal, thread seal, labyrinth seal, packing seal, dynamic seal, and mechanical seal.

1. Oil Seal

It is a self-tightening lip seal featuring a simple structure, compact size, low cost, and easy maintenance, with relatively low running torque. It can not only prevent medium leakage but also block the intrusion of external dust and other harmful substances, and has a certain compensation capacity for wear. However, it is not pressure-resistant, so it is generally used in low-pressure chemical pumps.

2. Gasket Seal

The gasket is a basic component for static sealing of centrifugal pumps and has an extremely wide range of applications. The selection of gaskets is mainly determined by factors such as the medium conveyed by the chemical pump, temperature, pressure, and corrosivity.

3. Thread Seal

There are generally two forms used in chemical pumps: one is threaded joint with gasket seal, and the other is thread seal with filler. Both are suitable for sealing small-diameter threaded connections. For the threaded joint with gasket seal, the gasket serves as the sealing element, while the thread only functions to provide clamping force.

4. Labyrinth Seal

When designed reasonably, manufactured precisely, assembled properly, and operated at a high rotational speed, the labyrinth seal can achieve excellent sealing performance. However, in practical applications, it often causes considerable leakage in chemical pumps, so it is not commonly used in chemical pump sealing systems.

5. Packing Seal

This seal involves placing compressible and resilient packing inside a stuffing box. The axial clamping force from the gland is converted into radial sealing force to achieve sealing. This method is called packing seal, and the packing used is referred to as sealing packing. Due to its simple structure, easy replacement, low cost, and wide adaptability to different rotational speeds, pressures, and media, packing seals are widely adopted in the design of chemical pumps.

6. Dynamic Seal

During the operation of the chemical pump, the pressure head generated by the auxiliary impeller balances the high-pressure liquid at the outlet of the main impeller, thereby realizing sealing. When the pump stops, the auxiliary impeller becomes ineffective, so a parking seal device must be equipped simultaneously to prevent potential pump leakage during shutdown. The auxiliary impeller seal has a simple structure, reliable sealing performance, and long service life, and can achieve zero leakage during pump operation. Therefore, it is often used in chemical pumps that convey media containing impurities.

7. Mechanical Seal

Currently, it is the most widely used sealing form in the chemical pump industry. Thanks to its advantages of minimal leakage and long service life, mechanical seals have become the primary shaft sealing method for such equipment worldwide. Also known as face seal, it is defined in relevant national standards as follows: A device that prevents fluid leakage, consisting of at least one pair of end faces perpendicular to the axis of rotation. These faces remain in contact and slide relative to each other under the action of fluid pressure, the elastic force (or magnetic force) of the compensation mechanism, and the cooperation of auxiliary seals.