How to prevent scaling on vacuum pumps
The vacuum pump is the workhorse of countless industrial processes—from chemical distillation and pharmaceutical drying to power generation and food processing. However, one of the most persistent and damaging threats to vacuum pump reliability is a problem that often goes unnoticed until it is too late: scaling.
Scale formation on the internal components of a vacuum pump does not happen overnight. It is a gradual process driven by the quality and temperature of the circulating cooling water. Over time, mineral deposits accumulate on impellers, casings, and other critical surfaces, reducing clearances, impairing heat transfer, and ultimately causing the vacuum pump to lose efficiency or seize entirely. In severe cases, scale deposits can reach thicknesses of 30 mm or more [2†L6], effectively destroying the internal clearances that the vacuum pump relies on for proper operation.
This article provides a comprehensive guide to preventing scaling on vacuum pumps, covering the root causes of scale formation, practical prevention strategies, and effective descaling methods. By understanding and implementing these measures, industrial operators can significantly extend the service life of their vacuum pumps and maintain reliable performance.
Understanding the Causes of Scaling in Vacuum Pumps
The formation of scale inside a vacuum pump is not random—it is the predictable result of specific operating conditions. Understanding these causes is the first step toward effective prevention.
The Role of Circulating Water Quality
The quality of the circulating cooling water is the single most important factor in scale formation. As one industry source explains: "The water quality and operating temperature of the circulating water exceeding a certain index are the main reasons for the fouling of the vacuum pump" [7†L3-L5].
Among water quality indicators, water hardness has the greatest impact on scale formation [7†L5-L6][9†L6-L7]. Hard water contains high concentrations of calcium and magnesium ions, which precipitate out of solution as the water is heated and concentrated within the vacuum pump. These precipitates form solid deposits—primarily calcium carbonate—that adhere to internal surfaces.
When hard water with higher hardness is used, "the scaling phenomenon is very serious, and the scale on the blades will thicken, which will inevitably reduce the effective space" within the vacuum pump [0†L9-L11]. Extremely hard water "may result in the formation of scale deposits on the internal pump parts, which will reduce the clearances and may cause the pump to lock up" [0†L31-L33][3†L9-L11].
The Impact of Operating Temperature
Temperature is the second critical factor in scale formation. The water ring inside a vacuum pump operates at elevated temperatures, and as the temperature rises, the solubility of calcium and magnesium salts decreases, causing them to precipitate out of solution and form scale.
The difference between the water ring temperature inside the vacuum pump and the temperature of the water in the softening pool is an important factor leading to scale formation [7†L19-L21][9†L19-L21]. Higher operating temperatures accelerate the precipitation of minerals, leading to more rapid scale buildup.
Industry recommendation: During circulating cooling water operation, it is necessary to monitor the return water temperature of each pump to ensure that it does not exceed 40°C [7†L24-L27][9†L24-L27][11†L23-L25].
The Similarity to Boiler Water Systems
The operating process of circulating water in a vacuum pump is "extremely similar" to the operating process of boiler water in a low-pressure hot water boiler [11†L9-L10][7†L10-L11][9†L10-L11]. This similarity is significant because it means the same water quality standards that apply to hot water boilers can be applied to vacuum pumps.
By managing the water quality of the vacuum pump according to hot water boiler water quality standards, operators can "prevent the vacuum pump from scaling and corrosion" [7†L12-L14][5†L8-L10][10†L12-L14].
Prevention Strategy 1 – Control Circulating Water Hardness
Reducing the hardness of the circulating cooling water is the most fundamental and effective measure for preventing scale formation in a vacuum pump.
Ion Exchange Water Treatment
The most comprehensive approach to hardness control is the installation of ion exchange water treatment equipment. Ion exchange systems replace calcium and magnesium ions in the water with sodium ions, effectively "softening" the water and eliminating the minerals that form scale.
When ion exchange equipment is used for water treatment, the circulating water maintains low hardness levels, dramatically reducing the potential for scale formation inside the vacuum pump.
Softening Pool and High-Level Pool Systems
In cases where ion exchange equipment cannot be installed due to cost or other constraints, a practical alternative is the use of a softening pool combined with a high-level pool [7†L16-L18][9†L16-L17][11†L14-L17].
How it works:
Softening pool: Water is stored and allowed to settle, reducing suspended solids and some hardness.
High-level pool: Provides gravity-fed water supply to the vacuum pump system.
While this approach is less effective than ion exchange, it provides a degree of water quality improvement that can slow scale formation.
Scale Inhibitors and Anti-Scalants
Chemical scale inhibitors can be added to the circulating water to prevent mineral precipitation. These chemicals work by interfering with the crystal growth of calcium carbonate and other scale-forming minerals, keeping them suspended in the water rather than depositing on vacuum pump surfaces.
Available products include:
Scale inhibition tablets such as CWP-TAB, designed specifically for circulating water in water-ring vacuum pumps, with a recommended dosing concentration of 20–25 ppm [4†L42-L44].
Anti-scalants and scale dispersants that prevent scale formation without harming the vacuum pump components [0†L18-L20].
Magnetic Water Treatment
Another emerging technology for scale prevention is magnetic water treatment. Magnetic water processors have been applied to water-ring vacuum pumps for scale removal and prevention, with studies demonstrating positive results through Raman spectroscopy, surface tension analysis, and field installation examples [6†L8-L10].
Prevention Strategy 2 – Control Circulating Water Temperature
Temperature control is the second critical pillar of scale prevention for vacuum pumps. By maintaining lower operating temperatures, operators can significantly reduce the rate of mineral precipitation and scale formation.
Monitoring and Controlling Return Water Temperature
During operation, it is essential to monitor the return water temperature of each vacuum pump to ensure that it does not exceed 40°C [7†L24-L27][9†L24-L27][11†L23-L25].
Practical measures:
Install temperature sensors on the return water lines of each vacuum pump.
Use valves to control water supply and maintain proper flow rates.
If return water temperature exceeds 40°C, supplement with low-temperature cold water or use other cooling methods to reduce the temperature [7†L28-L30][9†L27-L29][11†L26-L28].
Increasing Circulating Water Supply
"Improving the cooling effect through increasing the circulating water supply is an important guarantee for minimizing the rate of fouling" [7†L22-L23][9†L21-L22][11†L20-L21]. Higher flow rates improve heat dissipation, keeping the vacuum pump operating at lower temperatures and reducing scale formation.
Using Circulating Water Radiators
In applications such as coal mine gas drainage systems, the use of circulating water radiators has proven effective in controlling water temperature and preventing scale formation in water-ring vacuum pumps [0†L6-L7][8†L7]. Radiators dissipate heat from the circulating water before it returns to the vacuum pump, maintaining lower operating temperatures.
Prevention Strategy 3 – Regularly Flush the Pump Body
Regular flushing of the vacuum pump body is a simple but effective preventive measure that can be implemented with minimal cost and effort.
Using the Pump Body Drain Gate Valve
The drain gate valve on a vacuum pump body serves two purposes:
Normal discharge of water from the pump
Periodic flushing of dirt and water slag during operation [7†L31-L33][9†L30-L32][11†L29-L31]
By using the water pressure generated by the vacuum pump during operation, operators can periodically flush accumulated dirt and slag from the pump body. This practice serves two important functions:
Prevents dirt accumulation that can contribute to scale formation
Prevents water slag from converting into scale [7†L34-L36][9†L33-L34][11†L32-L33]
Establishing a Flushing Schedule
To be effective, pump body flushing should be performed on a regular schedule. The specific frequency depends on the water quality and operating conditions, but as a general guideline:
For systems with hard water or high operating temperatures: flush weekly or bi-weekly
For systems with treated water and moderate temperatures: flush monthly
Prevention Strategy 4 – Comprehensive Water Treatment
While temperature control and regular flushing are important, "water treatment is the most important link to prevent the pump body from scaling" [7†L38-L40][9†L37-L38][11†L37].
The Holistic Approach
The scaling problem of a vacuum pump "has its more complicated generation mechanism," and "correct analysis of water quality indicators and operating parameters is the key to finding correct preventive measures" [7†L36-L38][9†L34-L36][11†L34-L36].
A comprehensive water treatment program for a vacuum pump should include:
Regular water quality testing to monitor hardness, pH, and other key parameters
Appropriate treatment methods based on water quality results (ion exchange, chemical inhibition, magnetic treatment, etc.)
Ongoing monitoring of operating temperatures and flow rates
Periodic inspection of the vacuum pump internals for early signs of scale formation
Meeting Hot Water Boiler Water Quality Standards
As noted earlier, managing vacuum pump water quality according to hot water boiler standards can "prevent the vacuum pump from scaling and corrosion" [7†L12-L14][10†L12-L14][11†L11-L13]. These standards provide specific guidelines for hardness, pH, conductivity, and other parameters that ensure safe, scale-free operation.
For reference:
For pressurized hot water boilers, conductivity should be controlled below 50 μS/cm [5†L31-L33]
For medium-sized steam boilers, conductivity should be controlled below 20 μS/cm [5†L33-L34]
Descaling – When Prevention Is Not Enough
Despite the best preventive measures, scale may still form inside a vacuum pump over time. When this occurs, descaling is necessary to restore performance.
Mechanical Descaling
Mechanical cleaning involves physically removing scale from vacuum pump components. This can be done by:
Shoveling or scraping scale from accessible surfaces [0†L12]
Disassembling the pump and cleaning individual components
However, "mechanical cleaning obviously takes a lot of time because this approach cleaning requires equipment to be dismantled" [4†L31-L32].
Chemical Descaling
Chemical descaling uses acids or specialized cleaning solutions to dissolve scale deposits without disassembling the vacuum pump.
Common methods:
Rinsing with hydrochloric acid: Effective for removing calcium carbonate scale, but "after rinsing with hydrochloric acid, the residual hydrochloric acid must be rinsed with water" [0†L13-L14]
Citric acid solutions: A safer alternative for removing scale [2†L4-L6]
Specialized descaling fluids: Products such as DEKKER Vacuum's Scale-Ex are designed specifically for vacuum pump scale removal [3†L12]
Online descaling devices: Some systems allow automatic descaling without disassembly [4†L4-L10]
Precautions for Chemical Descaling
When using chemical descaling agents on a vacuum pump:
Ensure the descaling agent is compatible with the pump materials (seals, gaskets, impeller)
Use descaling agents with low corrosion rates that "do not harm seals and gaskets" [4†L33-L34]
Thoroughly rinse the vacuum pump after descaling to remove all residual chemicals
For heavy scale deposits, consider using multifunctional composite cleaning solutions designed for online cleaning [1†L34-L36]
Summary – A Comprehensive Approach to Vacuum Pump Scale Prevention
Preventing scale formation in a vacuum pump requires a systematic, multi-pronged approach:
Hardness control | Ion exchange, softening pools, scale inhibitors | Eliminates scale-forming minerals |
Temperature control | Monitor return water; keep below 40°C; increase circulation | Reduces precipitation rate |
Regular flushing | Use drain gate valve to flush during operation | Prevents dirt accumulation and scale conversion |
Water treatment | Comprehensive program per boiler standards | Addresses root causes of scaling |
Descaling | Mechanical or chemical removal when needed | Restores performance after scaling occurs |
Conclusion – Prevention Is the Best Protection
Scale formation is one of the most common and damaging threats to the reliable operation of a vacuum pump. The primary causes—hard water and elevated operating temperatures—are well understood and entirely preventable.
By implementing the strategies outlined in this article, industrial operators can protect their vacuum pumps from scale-related damage:
Control water hardness through ion exchange, softening pools, or chemical inhibitors
Monitor and control operating temperature to keep return water below 40°C
Flush the pump body regularly using the drain gate valve during operation
Implement comprehensive water treatment based on hot water boiler standards
Perform descaling when necessary using appropriate mechanical or chemical methods
The "scaling problem of vacuum pumps has its complicated formation mechanism" [7†L36-L37][11†L33-L34], but "the key to find out the correct preventive measures is to correctly analyze the water quality target and operation parameters" [11†L34-L36]. By understanding the causes of scale and taking proactive preventive measures, operators can significantly extend the service life of their vacuum pumps, reduce maintenance costs, and ensure consistent, reliable performance.
For any facility that relies on vacuum pumps for critical processes, scale prevention is not optional—it is essential. The small investment in water treatment and temperature control is far less than the cost of premature vacuum pump failure and unplanned production downtime.
