I. Instrument Overview

The KDN-380F automatic nitrogen analyzer (Kjeldahl nitrogen analyzer) is a specialized device designed for nitrogen content detection based on the classic Kjeldahl nitrogen determination method. It is widely used for the determination of crude protein in samples such as food, feed, grain and oil, agricultural products, soil, and fertilizers. It completes the release and absorption of ammonia through automatic alkali addition, steam distillation, and condensation collection, and can accurately calculate the nitrogen content of the sample with titration. The instrument is produced by Shanghai Zhiyue Scientific Instrument Co., Ltd. It features high levels of semi-automatic automation and stable operation. However, long-term exposure to strong acids, strong alkalis, and high-temperature steam conditions can easily cause pipeline corrosion, valve scaling, and pump aging. Systematic maintenance is a core means to extend equipment life and ensure the accuracy of detection data.

II. Immediate maintenance after daily use (mandatory)

(1) Cleaning of distillation pipeline

1. After distillation is complete, place an empty digestion tube, activate the steam mode, and use pure water to continuously steam rinse the distillation chamber and steam pipeline for 3 to 5 minutes to remove residual ammonia, alkali solution, and acid mist, thus preventing long-term corrosion of the glass inner tube and silicone hose by strong alkali;

2. Drain the alkali solution (NaOH) pipeline separately: Long press the alkali addition button to fully drain the remaining sodium hydroxide from the pipeline, preventing alkali solution crystallization from blocking the micro pump, which is the most common cause of failure for this model.

(II) Component cleaning and repositioning

1. Digestive tube, receiving conical flask: Immediately rinse with tap water, and use detergent such as dishwashing liquid to clean the bottle. Rinse with pure water, invert and let it dry. It is forbidden to leave waste liquid in the bottle for a long time;

2. Safety door cavity: Wipe off the alkali solution and boric acid absorption solution splashed inside, and dry the water stains;

3. Condensate water pipeline: When the instrument is not in use for an extended period, the condensate water can be drained. Disconnect the inlet and outlet pipes, and use an ear syringe to blow air into the water outlet. The condensate water will then be drained from the water inlet.

(III) Circuit and air source inspection

Turn off the main power switch of the host and the external main power supply, check if the power socket on the right side and the heating indicator light are working properly, and ensure that the panel buttons are not splashed with liquid. If there are reagent droplets, wipe them off with a dry cloth immediately.

III. Weekly in-depth maintenance

1. Thoroughly unblock and maintain the reagent pipeline

• Alkali solution tank and boric acid absorption solution tank: Empty them completely, clean the inner walls of the tanks, and replace with freshly prepared reagents; remove the suction filter head, and ultrasonically clean the filter screen with pure water to prevent impurities from being sucked into the pump and causing blockage;

• Dredging of pipeline crystallization: If the addition of alkali is not effective, boiled water can be added to dissolve the crystallization, followed by rinsing with a large amount of pure water.

2. Scale removal of steam generator (heating furnace body)

KDN-380F relies on a built-in heating furnace to generate saturated steam. If the water is not drained for a long time, it is prone to deterioration, leading to reduced heating efficiency, burned heating tubes, and insufficient steam volume

1. Drain the residual water from the steam boiler and add an aqueous solution of citric acid descaler (concentration 5% to 10%), soaking for half an hour;

2. The steam generator can be disassembled, and the glass wall thoroughly brushed with a brush. Afterwards, it should be rinsed multiple times with pure water until there is no sour taste;

3. It is recommended to use distilled water/deionized water for the steam oven on a daily basis to reduce scale formation from the source. It is advised to drain the water from the steam generator 1-2 times a week.

3. Inspection of sealing rings and transmission components

Check the clamping seal ring of the digestive tube for aging, cracking, and air leakage. If there is any decrease in elasticity or leakage, replace it immediately.

IV. Regular monthly maintenance and inspection

1. Troubleshooting of pipeline aging: Inspect each internal rubber hose, delivery hose, and steam connecting pipe one by one. Replace any that exhibit hardening, bulging, cracks, or leakage to prevent strong alkali leakage from corroding the internal circuit board of the instrument;

2. Solenoid valve and dosing pump: Test whether the alkali dosing is smooth, and regularly clean the alkali solution pump. The solenoid valve prevents foreign objects from entering the air inlet;

3. Electrical safety inspection: Check the insulation of the heating tube and the outer layer of the power cord for any damage to avoid the risk of short circuit and electric leakage;

4. Condensation system inspection: Observe whether there is scale attached to the condensation jacket, and check the smoothness of the water passage on the outer wall. Poor condensation effect will directly lead to lower detection results.

V. Sealing and maintenance for long-term shutdown (over 15 days)

1. Repeat rinsing with pure water for the entire pipeline, and drain all liquids from all reagent buckets, steam boilers, and pipelines;

2. Clean and dry the digestive tube and conical flask, then place them in the storage cabinet. Wipe the sealing ring clean to prevent adhesion and aging;

3. Clean the entire instrument thoroughly, ensure the interior of the chamber is dry and well-ventilated, put on a dust cover, and place it in a dry, dark laboratory environment free from volatile acids and alkalis;

4. Before reuse, conduct three blank distillations to verify steam stability and liquid addition accuracy before officially testing samples.

VI. Usage and maintenance taboos (key precautions)

1. It is prohibited to allow high-concentration strong alkali to remain in the pipeline for an extended period of time. The alkali solution pipeline must be emptied daily after use;

2. It is strictly prohibited to use strong acid for direct heating and steaming for descaling, to avoid corroding the heating liner;

3. During operation, the safety door must not be opened, as high-temperature steam can easily cause burns and affect distillation pressure;

4. Reagents must be prepared according to specifications: sodium hydroxide solution should be avoided to prevent sodium carbonate crystals from precipitating and blocking the pipeline, and boric acid absorption solution should be replaced regularly to prevent mold growth;

5. The environment should be protected from direct sunlight, corrosive gases, and high humidity to prevent the aging of the panel's digital display and the rusting of the box body.

VII. Maintenance Summary

The KDN-380F automatic nitrogen analyzer is a wet chemical precision analysis device, and corrosion, scaling, and pipeline blockage are the main causes of wear and tear. Adhering to a maintenance system that includes daily cleaning, weekly descaling, monthly overhaul, and standardized handling for long-term storage can not only ensure the parallelism and recovery rate of crude protein detection data, but also significantly reduce the replacement frequency of vulnerable parts such as solenoid valves, heating tubes, and liquid dispensing pumps, thereby enhancing the stability and service life of the instrument.