The 6 Reasons for Regularly Cleaning the Diesel Tank of a High-Pressure Common Rail Test Bench

The high-pressure common rail test bench is a core precision device for testing and calibrating diesel injectors and high-pressure fuel pumps. The stability of its operation and the accuracy of test data depend entirely on a clean and stable fuel supply environment. As the source of fuel storage and supply, the diesel tank of the test bench continuously accumulates metal debris and sludge during long-term operation, while also breeding moisture and microorganisms, gradually causing a series of problems such as fuel deterioration, fuel system contamination, and component wear. Most equipment failures, test data deviations, and high-frequency maintenance losses stem from fuel system contamination caused by a long-term uncleaned fuel tank. To ensure the lifespan of the test bench's precision components, maintain stable testing accuracy, and reduce operating costs, regular cleaning of the diesel tank is an indispensable core maintenance item for high-pressure common rail test benches. The specific core reasons and quantitative basis are as follows:

1. Protecting the Precision Components of the High-Pressure Fuel Pump and Injector Components

The gap between components in the high-pressure common rail system is only 1.5–3.7 micrometers, making it extremely sensitive to impurities. Hard particles such as metal shavings, rust, and gum deposited at the bottom of the fuel tank can enter the high-pressure fuel pump plunger, delivery valve, and injector needle valve along with the fuel, causing abrasive wear, scratches, and jamming. This leads to component seal failure, difficulty in pressure build-up, and poor fuel atomization, ultimately resulting in serious malfunctions such as fuel pump seizure and injector failure.

1.1. Fitting Clearance Parameters

• The fitting clearance of the high-pressure fuel pump plunger assembly and injector needle valve assembly is only 1.5–3.7 μm, far exceeding the filtration accuracy of conventional filter elements. Metal shavings and sand particles (generally larger than 2 μm in diameter) deposited in the fuel tank can directly enter the mating surfaces.

1.2. Percentage of Wear-Related Failures

• In equipment where the fuel tank is not cleaned regularly, the percentage of failures due to abrasive wear and jamming of components reaches 68%; after regular fuel tank cleaning, this type of failure drops to less than 9%.

1.3. Component Lifespan Comparison

• Severe fuel tank contamination: The average lifespan of precision components in the fuel pump and injectors is shortened by more than 60%, with sealing failure and jamming occurring within 3-6 months.
• Regular cleaning: Components can maintain a normal lifespan of 18-24 months (standard cycle).

1.4. Performance Loss Data

• After impurities cause scratches on components, the high-pressure system's pressure build-up efficiency decreases by 12%-25%, and the idle pressure holding leakage exceeds the standard by 0.3-0.8 mL/min, directly causing functional failure of the components.

1.5. Maintenance Cost Data

• Replacing the entire high-pressure fuel pump and injector assembly due to wear caused by impurities costs 8-12 times more in materials and labor than the cost of regular fuel tank cleaning.

2. Stable Common Rail Pressure, Ensuring Test Accuracy

The core of the test bench is stable high-pressure (±0.1 MPa) and precise flow control. Impurities and moisture in the fuel tank can clog the low-pressure fuel line, filter, and common rail, causing poor fuel supply, pressure fluctuations, and flow drift. This directly leads to distorted test data (such as injection quantity deviation and abnormal pressure curves), affecting the accuracy of injector calibration and even misjudging qualified parts as unqualified.

2.1. Pressure Fluctuation Difference:

• Standard operating conditions require common rail pressure fluctuation ≤ ±0.1 MPa; when the fuel tank is contaminated or the fuel line is blocked, pressure fluctuation can reach ±0.4～±0.7 MPa, exceeding the acceptable threshold by several times.

2.2. Injection Quantity Deviation

• Unstable fuel supply due to blocked fuel lines results in a single-cycle injection quantity deviation of 3%～8%, exceeding the equipment calibration allowable error (≤1.5%).

2.3. Test False Judgment Rate

• Without regular fuel tank cleaning, the injector test false judgment rate reaches 22% (qualified parts are judged as unqualified, and faulty parts are missed); after standardized cleaning, the false judgment rate drops to below 2%.

2.4. Pressure Response Time

• Accumulated dirt and clogging can cause a pressure build-up response delay of 0.2–0.5 seconds, distorting the dynamic pressure curve and failing to meet high-precision calibration requirements.

2.5. Data Repeatability

• Under dirty conditions, the data dispersion of three consecutive tests for the same sample is >2.5%; under clean oil circuit conditions, the dispersion is stable at ≤0.8%, meeting test consistency standards.

3. Preventing Frequent Filter Clogging and Reducing Maintenance Costs

Long-term accumulation of sludge, sediment, and microbial slime (diesel bacteria) at the bottom of the fuel tank can quickly clog the coarse and fine filters, leading to a sharp decrease in filter element life (clogging within 100 hours from a normal 500 hours), requiring frequent filter element replacements and increasing consumable costs. Simultaneously, clogging increases fuel supply resistance, raises the fuel pump load, and causes motor overheating, resulting in additional downtime and maintenance costs.

3.1. Filter Element Lifespan

• Severely clogged oil tank: Filter elements become clogged and fail after an average of 80–120 hours of use.
• Regularly clean the oil tank: Filter element lifespan can reach 480–520 hours, an increase of approximately 300%–550%.

3.2. Filter Element Replacement Frequency

Based on 2000 hours of operation per year:

• Clogged state: Filter elements need to be replaced approximately 17–25 times per year.
• Clean state: Replacement only about 4 times per year, a reduction of over 75%.

3.3. Consumable Costs

• The average price of a single set of coarse + fine filter elements is fixed, reducing annual filter element procurement costs by over 70%.

3.4. Equipment Load and Energy Consumption

• Clogged filters increase oil supply resistance, increase oil pump load, and increase overall machine power consumption by 10%–18%; simultaneously, the failure rate of the motor and oil pump increases by 32%, resulting in increased additional maintenance time and parts costs.

3.5. Downtime Excessive

• Frequent filter replacements and oil line blockage repairs result in an average of 60–90 hours of additional downtime annually. With proper cleaning, this downtime is reduced to less than 10 hours, effectively improving equipment uptime.

4. Removing Moisture and Microorganisms to Prevent System Corrosion

Diesel fuel readily absorbs water, forming a free water layer at the bottom of the tank, which breeds microorganisms (fungi/bacteria), generating acidic metabolites and biofilms. Moisture and acidic substances corrode the tank walls, fuel lines, pump housing, and injector valves, producing new rust and creating a vicious cycle of corrosion → impurities → wear.Moisture also impairs fuel lubricity, exacerbating dry friction between components, inducing cavitation and cavitation, and shortening component lifespan.

4.1. Fuel Water Content Threshold and Hazards

• Equipment requires diesel fuel water content ≤50ppm. If the tank is not cleaned regularly, water accumulation at the bottom can cause local water content to rise to 300–800ppm, far exceeding safety standards. Moisture disrupts oil film lubrication, increasing the dry wear rate of components by 40%–60%.

4.2. Corrosion Rate Comparison

• In environments with moisture and microbial growth, the corrosion rate of oil pipes, pump housings, and the inner wall of the oil tank accelerates by 2.8 times. The resulting rust and corrosion debris continuously mix into the oil circuit, causing secondary pollution.

4.3. Component Failure Rate

• Valve jamming and seal leakage caused by rust and pitting account for 35% of failures under dirty oil tank conditions; after regular water and dirt removal, this type of failure drops to below 6%.

4.4. Impact of Microbial Derivatives

• Accumulated water breeds microorganisms, generating acidic substances that increase the oil's acidity by 0.25–0.4 mg KOH/g, accelerating the aging of rubber seals and shortening their service life by 50%.

4.5. Cavitation/Cavitation Damage

• Moisture entering the high-pressure fuel system easily causes cavitation, resulting in cavitation pits on the plunger and injector inner walls. This increases high-pressure leakage by 0.4–1.0 mL/min, directly causing component failure.

5. To prevent fuel degradation and to prevent gum buildup that clogs the fuel lines

Diesel fuel that has been left stagnant for a long time will oxidize and deteriorate, producing gum and asphaltenes. These substances mix with impurities to form sludge, which settles at the bottom of the fuel tank. This sludge can adhere to the walls of fuel lines, filters, and injector nozzles, causing blockages in the injectors, sticking of the needle valves, and poor atomization. This can lead to uneven fuel injection, black smoke, and abnormal fuel return during testing. In severe cases, the entire fuel system may need to be disassembled and cleaned.

5.1. Changes in Gum Content

• The national standard for qualified diesel fuel is ≤25 mg/100 mL; after the fuel tank is not cleaned for a long time and the fuel oxidizes, the gum content rises to 70–120 mg/100 mL, exceeding the standard by more than 2.8 times.

5.2. Impact of Nozzle Clogging

• Gum buildup reduces the injector nozzle flow area by 15%–40%, resulting in a 12%–35% decrease in fuel flow and severely degraded atomization.

5.3. Needle Valve Sticking Failure Rate

• Under gum-accumulated conditions, injector needle valve sticking and sticking account for 41% of failures; after regular tank cleaning and fuel replacement, this failure rate drops to below 5%.

5.4. Fuel Circuit Flow Resistance

• Gum sludge adhering to the pipe walls increases low-pressure fuel circuit resistance by 22%–38%, significantly reducing fuel supply flow stability.

5.5. Frequency and Cost of Disassembly and Cleaning

• When the fuel tank is contaminated or the fuel is deteriorated, the entire fuel circuit requires disassembly and cleaning 5–7 times per year; with proper maintenance, this is reduced to only once per year, reducing cleaning time and consumable costs by over 80%.

5.6. Fuel Shelf Life

• In a sealed, clean fuel tank, diesel fuel has an effective service life of approximately 90 days; in environments with accumulated dirt and water, fuel will show significant deterioration and gum formation within 30 days.

6. Eliminating Safety Hazards and Extending Equipment Lifespan

Long-term accumulation of impurities, moisture, and sludge in the fuel tank can lead to:

• Fuel line blockage → fuel pump overload → motor burnout, pipe rupture;
• Moisture corrosion → fuel tank perforation and leakage → fire and environmental pollution risks;
• Microbial growth → fuel deterioration → abnormal combustion → equipment vibration and abnormal noise.

Regular cleaning can thoroughly eliminate hidden dangers, ensure the long-term stable operation of the test bench, extend the overall service life of the machine, and reduce downtime losses caused by sudden failures.

In summary, as the source of the high-pressure common rail test bench's fuel supply system, the cleanliness of the diesel tank directly determines the lifespan of equipment components, testing accuracy, maintenance costs, and operational safety. Fuel tank contamination is not merely a problem with the fuel system; it creates a vicious cycle of "impurity wear, water corrosion, gum blockage, data distortion, and frequent malfunctions," continuously impacting the core performance and production efficiency of the equipment. Therefore, regularly and thoroughly cleaning, removing water, gum, and impurities from the diesel tank is the most cost-effective and crucial basic task in the daily maintenance of high-pressure common rail test benches. Through standardized and routine tank cleaning and maintenance, various equipment failures can be avoided at the source, testing and calibration accuracy can be stabilized, consumable, repair, and downtime costs can be significantly reduced, maximizing the equipment's value and ensuring efficient, accurate, and safe testing.

Written by

Taian Crystal Automation Co., Ltd.

Editor Chen

www.crystalautotest.com

WhatsApp:+86 185 9528 8526

Email:martin@crystalautotest.com