Abnormal pressure of refrigerated dryer? It may be caused by these 3 reasons

In modern industrial production, compressed air is one of the important power sources and is widely used in various fields. The quality of compressed air directly affects the service life of pneumatic equipment and the efficiency of the production process. As a key equipment for handling moisture in compressed air, the stable operation of refrigerated dryers is essential. However, in actual operation, refrigerated dryers occasionally have abnormal pressure problems, which not only affects the drying effect, but may even cause equipment damage or production interruption. This article will explore in depth the common causes, diagnostic methods, symptoms and preventive measures of abnormal pressure of refrigerated dryers, aiming to help readers better understand and maintain refrigerated dryers and ensure their efficient and stable operation.

Overview of the working principle of refrigerated dryers: the cornerstone of understanding pressure

To explore the abnormal pressure of refrigerated dryers in depth, we must first have a clear understanding of their core working principles. As the name suggests, refrigerated dryers “dry” compressed air by “freezing”. The essence of refrigeration technology is to reduce the temperature of compressed air to below the dew point of water vapor, forcing it to condense into liquid water and separate and discharge. This process is a sophisticated physical cycle involving complex heat exchange between gas, liquid and refrigerant.

Its workflow can usually be broken down into the following key stages:

Heat exchange and initial cooling (precooler/air-to-air heat exchanger):

Untreated hot and humid compressed air (usually at a high temperature and rich in water vapor, oil mist and a small amount of solid particles) coming out of the air compressor will first enter the precooler inside the refrigerated dryer. This precooler is usually an efficient air-to-air heat exchanger. Here, the hot and humid air at the inlet does not directly contact the refrigerant, but is countercurrently heat exchanged with the low-temperature cold air that has been dried and is about to be discharged from the dryer.

Function: This design has two benefits:

Precooling: Preliminary reduction of the temperature of the hot and humid air at the inlet, reducing the load of the subsequent refrigeration system, thereby improving overall energy efficiency.

Rewarming: Raise the temperature of the dried cold air to close to the ambient temperature (usually higher than the dew point) to prevent the dry air from condensing again in the external pipeline after being discharged from the dryer, protecting the downstream gas point.

At this stage, the pressure change of the air is relatively small, and the main thing is the transfer of temperature.

Deep cooling and water vapor condensation (evaporator/air-refrigerant heat exchanger):

The compressed air that has been initially cooled by the precooler then enters the heart of the dryer – the evaporator. The evaporator is a highly efficient air-refrigerant heat exchanger. Here, the compressed air exchanges heat with the liquid refrigerant from the refrigeration system in a low-temperature and low-pressure state. The liquid refrigerant absorbs the heat of the compressed air inside the evaporator and evaporates (gasifies), becoming a low-temperature and low-pressure gaseous refrigerant.

Function: After losing a lot of heat, the temperature of the compressed air will drop sharply, usually to a dew point temperature of 2°C to 10°C (depending on the design and environmental conditions). When the temperature is lower than its pressure dew point, the supersaturated water vapor in the compressed air will condense into tiny liquid water droplets. At the same time, some oil vapor will also condense into oil mist or liquid oil droplets.

This stage is the core drying process. In terms of pressure, the gas flows from the high-temperature area to the low-temperature area, accompanied by volume contraction (water vapor condensation).

Air-water separation (air-water separator):

The compressed air coming out of the evaporator is already very humid and carries a large amount of condensed water and oil droplets. These humid air will immediately enter a specially designed air-water separator. The air-water separator usually uses the principles of centrifugation, collision or coalescence to separate the water and oil droplets with larger specific gravity from the airflow.

Function: Efficiently separate liquid water and oil from the compressed air to prevent them from entering the downstream system with the airflow. The separated water and oil will gather at the bottom of the separator.

At this stage, the air may produce a slight pressure loss when passing through the structure of the separator.

Automatic drainage (automatic drain valve):

The water and oil accumulated at the bottom of the air-water separator will be discharged to the outside of the dryer regularly or continuously through an automatic drain valve (usually float type, electric or electronic type).

Function: Ensure that the condensed water and oil are discharged in time to prevent them from being carried away by the airflow again, or accumulate too much to affect the separation effect or even blockage.

The normal operation of the drain valve is essential to maintain the balanced pressure and drying effect inside the dryer.

Reheating and discharge:

After the air-water separation and water discharge, the dry cold air returns to the precooler again, and conducts secondary heat exchange with the hot and humid air at the inlet to absorb heat.

Function: The temperature of the dried air rises to close to the ambient temperature (usually 20-30°C), which not only recovers part of the cold capacity and reduces energy consumption, but more importantly, it avoids the “secondary condensation” (i.e. condensation on the outer wall of the pipe) caused by the temperature difference on the connecting pipe after the dry air is discharged from the dryer, which is a phenomenon that needs to be avoided in many industrial applications.

Finally, the temperature-recovered, dry and clean compressed air is discharged through the outlet of the dryer and sent to the gas point.

Composition of the refrigeration cycle: The above cooling process is supported by a complete refrigeration cycle system, which consists of a refrigeration compressor, a condenser, an expansion valve and an evaporator. The refrigeration compressor is responsible for compressing the gaseous refrigerant into high-temperature and high-pressure gas; the condenser cools and liquefies the high-temperature and high-pressure gas; the expansion valve throttles and depressurizes the high-pressure liquid refrigerant and cools it; the evaporator absorbs heat to evaporate the refrigerant. The efficiency and stability of this cycle directly determine the cooling capacity and overall performance of the dryer.

Understanding these principles is the basis for diagnosing abnormal pressure problems. Problems in any link may affect the smoothness of the airflow or the refrigeration efficiency, thus manifesting as abnormal pressure.

Common causes of abnormal pressure in refrigerated dryers

Abnormal pressure in refrigerated dryers can usually be attributed to the following three main reasons:

Filter blockage: the invisible killer of pressure drop

The filter is an important part of the refrigerated dryer, used to filter particulate matter, oil and moisture in the compressed air to protect subsequent equipment. However, if the filter is not cleaned or replaced for a long time, its filter element will gradually be blocked by pollutants, resulting in increased resistance to air passing, thereby causing pressure drop.

Inlet filter blockage: If the filter at the inlet of the dryer is blocked, the air flow entering the dryer will be reduced, and the inlet pressure may increase, while the outlet pressure will be relatively reduced, forming a pressure difference.

Internal filter blockage in the cold dryer: Some cold dryers also have filters inside. If these internal filters are blocked, they will also hinder the airflow and cause internal pressure drop.

Drain outlet blockage: The drain valve or drain pipe is blocked, resulting in the condensate being unable to be discharged smoothly, accumulating in the filter or separator, which will also increase the airflow resistance and cause pressure fluctuations.

Refrigeration system failure: the key to affecting dew point and pressure

The refrigeration system is the “heart” of the refrigerated dryer, and its normal operation directly determines the dew point and outlet pressure of the dryer. Refrigeration system failure will lead to poor refrigerant circulation and reduced refrigeration capacity, which will in turn affect the cooling effect of compressed air and even cause pressure imbalance inside the system.

Insufficient or leaking refrigerant: Refrigerant is the medium of the refrigeration cycle. If the refrigerant charge is insufficient or there is a leak in the system that causes the refrigerant to be lost, the refrigeration capacity will decrease, the evaporator temperature will not reach the preset value, thereby affecting the drying effect and may cause the evaporation pressure to be too low.

Refrigeration compressor failure: The compressor is the power source of the refrigeration system and is responsible for compressing the refrigerant gas. If the compressor is worn, the valve plate is damaged, or the motor fails, it will lead to insufficient compression capacity, the pressure on the high-pressure side may decrease, and the pressure on the low-pressure side may increase, affecting the entire refrigeration cycle.

Poor heat dissipation of the condenser: The condenser is responsible for cooling and condensing the high-temperature and high-pressure refrigerant gas. If the condenser heat dissipation fins are dirty, the fan fails, or the cooling water (for water-cooled) flow is insufficient, the condensing pressure will be too high, affecting the refrigeration efficiency, and even causing high-pressure protection shutdown.

Expansion valve failure: The expansion valve is used to adjust the refrigerant flow. If the expansion valve is improperly opened (too large or too small) or blocked, it will cause insufficient or excessive refrigerant supply, affecting the refrigeration effect of the evaporator and causing abnormal evaporation pressure.

Dry filter (inside the refrigeration system) is blocked: There is also a dry filter inside the refrigeration system to absorb moisture and impurities in the refrigerant. If it is blocked, it will limit the flow of refrigerant, resulting in a decrease in refrigeration effect and affecting system pressure.

Pneumatic pipeline or valve problem: interference from external factors

In addition to the problem of the dryer itself, the external pneumatic pipeline or valve connected to the dryer may also cause abnormal pressure.

Pipeline leakage: If there is a leak in the compressed air pipeline, the outlet pressure will drop, especially when the gas consumption is large, the pressure drop will be more obvious.

Valve blockage or failure: If the ball valve, butterfly valve or check valve at the inlet and outlet of the dryer is not fully opened, blocked by foreign objects or has a fault, it will hinder the airflow and cause pressure drop or back pressure.

Post-processing equipment blockage: If other air source processing equipment (such as precision filters, air storage tanks, etc.) is connected to the rear of the refrigerated dryer, the blockage of these equipment will also affect the outlet pressure of the dryer.

Fluctuation of gas consumption: If the downstream gas consumption suddenly increases significantly, exceeding the processing capacity of the dryer, it may also cause a short-term drop in outlet pressure.

How to diagnose the pressure problem of the refrigerated dryer? : From the outside to the inside, scientific investigation

In the face of abnormal pressure in the refrigerated dryer, it is crucial to conduct a systematic and scientific diagnosis, which helps to quickly locate the problem and take effective solutions. The following are some key diagnostic steps and methods:

Observe the instrument readings: preliminary judgment and data support

This is the most direct and basic diagnostic method. Refrigerated dryers are usually equipped with multiple pressure gauges. Carefully observing and recording their readings is the first step to discover abnormalities.

Inlet pressure gauge: Check the pressure of compressed air entering the dryer. If this pressure is significantly lower than the air compressor outlet pressure or the system set pressure, the problem may be in the main line, pre-filter or valve before the dryer.

Outlet pressure gauge: Check the pressure of compressed air discharged from the dryer after drying.

Inlet and outlet pressure difference analysis: Compare the readings of the inlet and outlet pressure gauges.

Normal pressure difference: For a well-functioning dryer, the inlet and outlet pressure difference is usually between 0.02MPa and 0.03MPa (the specific value depends on the model and design).

Pressure difference is too large: If the pressure difference is significantly beyond the normal range (for example, reaching 0.05MPa or even higher), it strongly suggests that there is a serious obstruction in the air flow channel, and the first suspect is the filter blockage. The focus should be on checking whether the pre-filter, the internal filter of the dryer, and the automatic drain valve are blocked.

Refrigeration system high pressure gauge: monitors the pressure of the refrigerant in the condenser.

High pressure is too high: It may mean that the condenser is not dissipating heat well (such as dirty fins, fan failure, insufficient cooling water/dirty blockage), too much refrigerant is charged, or there is non-condensable gas in the system.

High pressure is too low: It is relatively rare and may be related to severe refrigerant shortage or inefficient refrigeration compressor.

Refrigeration system low pressure gauge: monitors the pressure of the refrigerant in the evaporator.

Low pressure is too low: This is a typical manifestation of insufficient refrigerant, small expansion valve opening/blockage, evaporator frosting, or refrigeration compressor suction valve failure. Too low low pressure may cause the evaporator to freeze, further blocking the airflow.

Low pressure is too high: it may be related to the expansion valve opening being too large, the heat load being too large (such as the compressed air temperature being too high, the flow being too large), and the performance degradation of the refrigeration compressor.

Auditory and visual inspection: sensory clues

In addition to the instrument, our senses can also provide valuable clues.

Abnormal noise: listen carefully to the running sound of the dryer.

Refrigeration compressor: If you hear abnormal friction, knocking, humming or periodic noise, it may indicate a mechanical failure or motor problem inside the compressor.

Fan: Check whether the cooling fan has abnormal noise, such as the squeaking sound of worn bearings, or the sound of blades rubbing against the shell.

Refrigerant leakage: Some refrigerant leakage points may emit a faint “hissing” sound.

Drain valve: Is there an abnormal stuck sound or continuous air leakage sound when the automatic drain valve is activated (which may indicate a leak).

Visual inspection:

Condenser: Check whether the condenser fins are heavily blocked by dust, oil, catkins, etc., which will seriously affect heat dissipation.

Fan: Confirm whether the cooling fan is running normally, whether the rotation direction is correct, and whether the air volume is sufficient.

Pipeline: Check whether there are oil stains (leakage points) and frost on the refrigerant pipeline (may indicate refrigerant leakage or evaporator freezing). Check whether there are obvious leaks in the compressed air pipeline (can be tested with soapy water).

Drain valve: Observe whether the automatic drain valve can drain condensed water regularly. If no water is discharged, or the water is continuously drained but the flow rate is slow, it may be blocked or faulty.

Sight glass (if any): Observe the refrigerant sight glass. If you see continuous and large bubbles, it usually indicates insufficient refrigerant.

Temperature measurement: Thermodynamic evidence

Temperature is a key parameter that reflects the thermodynamic state of the system.

Compressed air inlet and outlet temperature: Use a thermometer to measure the temperature of the compressed air entering and exiting the dryer.

Inlet temperature is too high: It may exceed the design range of the dryer, resulting in excessive refrigeration load, affecting the drying effect and pressure.

Outlet temperature is too high: It indicates poor drying effect, which may be related to refrigeration system failure.

Temperature at key points of the refrigeration system: measure the exhaust temperature of the refrigeration compressor, the outlet temperature of the condenser, the inlet temperature of the expansion valve, the outlet temperature of the evaporator, etc.

Exhaust temperature is too high: it may be related to poor heat dissipation of the condenser, insufficient refrigerant, and low efficiency of the compressor.

Evaporator outlet superheat: superheat is an important indicator to determine whether the expansion valve adjustment is appropriate. Too low superheat may lead to wet compression, and too high superheat indicates insufficient evaporator utilization.

Current detection: feedback of power

Measure the operating current of the refrigeration compressor and fan motor.

Compressor current:

Too high current: it may mean that the compressor is overloaded (such as high voltage, too low voltage), or internal mechanical failure.

Too low current: it may mean that the compressor is running at no load (such as serious refrigerant leakage), or motor failure.

Fan current: check whether the fan motor is normal and whether the current is within the rated range.

One-by-one investigation and cross-validation: logical reasoning

According to the above preliminary diagnosis results, carry out targeted one-by-one investigation.

Suspected filter blockage: Try to clean or replace the relevant filter element, and then observe the pressure difference change.

Suspected refrigerant shortage/leakage: Ask professionals to use a leak detector to detect the leak point, vacuum and charge sufficient refrigerant after repair.

Suspected condenser heat dissipation problem: Clean the condenser and check the fan operation.

Suspected drain valve failure: Check whether the drain valve is stuck, or manually test its drainage function.

Suspected external pipeline: Perform a leak test on the main pipeline.

During the troubleshooting process, only change one variable at a time and observe its impact on pressure and other parameters, which will help to locate the problem more accurately.

Common abnormal pressure symptoms: Interpretation of warning signals

Understanding the typical symptoms of abnormal pressure in refrigerated dryers can help operators find problems at the first time and avoid the expansion of faults. These symptoms are the equipment’s “help” signal:

The inlet and outlet pressure difference is too large (or the outlet pressure is continuously low):

This is the most direct and obvious symptom of abnormal pressure. If the inlet pressure is normal, but the outlet pressure is significantly lower than the inlet pressure, and the pressure difference between the two is far beyond the normal range (for example, more than 0.05MPa or even more), it can almost be concluded that there is a serious obstruction in the air flow channel.

Implied problem: There is a high probability that the filter element is seriously blocked (including the pre-filter and the filter inside the cold dryer), and the second possibility is that the inlet and outlet valves are not fully opened, or the pipeline is severely narrowed locally.

Impact: It causes insufficient pressure at the downstream gas point, affects the performance of pneumatic equipment, and increases the energy consumption of the air compressor.

The high pressure of the refrigeration system is too high (frequent high-pressure protection shutdown):

The high-pressure gauge reading of the refrigeration system is continuously higher than the normal range (for example, more than 2.0MPa or even higher), and the cold dryer may be accompanied by frequent “high-pressure protection” alarms and shutdowns.

Implied problem: It is usually related to poor heat dissipation of the condenser (fin blockage, fan failure, high ambient temperature) or excessive refrigerant filling. It may also be that there is non-condensable gas inside the refrigeration system.

Impact: The compressor runs at high load for a long time, shortens its life, increases energy consumption, and reduces refrigeration efficiency.

Low pressure in the refrigeration system (evaporator icing):

The reading of the low pressure gauge of the refrigeration system is continuously lower than the normal range (for example, lower than 0.2MPa, or even negative pressure), and may be accompanied by frost or even ice on the surface of the evaporator (usually located inside the dryer).

Implied problem: The most common cause is insufficient or leaking refrigerant, followed by too small or partial blockage of the expansion valve, or blockage of the drying filter inside the refrigeration system.

Impact: The icing of the evaporator will cause further blockage of the air flow channel and aggravate the pressure drop. At the same time, the refrigeration capacity is seriously insufficient, which directly leads to an increase in the exhaust dew point and poor drying effect.

Increased exhaust dew point or water in downstream equipment:

Although this is not a direct symptom of pressure, it is the most direct consequence of abnormal pressure (especially abnormal pressure in the refrigeration system). The humidity of the compressed air at the outlet of the dryer increases significantly, water accumulates in the pipes at the gas point, and even water marks or rust appear on downstream precision equipment (such as cylinders and pneumatic valves).

Implied problem: Refrigeration system failure leads to poor cooling effect and inability to effectively remove moisture. This is often closely related to the high and low pressure abnormalities of the refrigeration system.

Impact: Seriously damage the life and performance of pneumatic equipment, affect product quality, and may cause production accidents.

Frequent start-stop or alarm of equipment:

When the dryer is running, if the start-run-stop cycle (triggered by the protection device) frequently occurs, or the controller displays various fault codes and alarm messages.

Implied problem: Abnormal pressure (such as high pressure too high, low pressure too low) often triggers the machine’s protection mechanism, causing the equipment to automatically shut down to avoid damage.

Impact: Affect production continuity and increase equipment maintenance costs.

Increased energy consumption of compressed air system:

Although not directly reflected on the pressure gauge, if the air compressor is frequently loaded to maintain system pressure, the running time is extended, or the current consumption of the dryer itself increases, it may be an increase in hidden costs caused by abnormal pressure (especially pressure drop).

Implied problem: Air line blockage, leakage or low refrigeration efficiency will force the system to consume more energy to achieve or maintain the original performance.

Impact: Increased operating costs and reduced economic benefits.

How to prevent abnormal pressure in refrigerated dryers? : Prepare for a rainy day, long-term management

Prevention is better than cure. By implementing a comprehensive and systematic preventive maintenance strategy, the risk of abnormal pressure in the refrigerated dryer can be minimized to ensure its long-term stable and efficient operation.

Strictly implement the regular cleaning and replacement system of filters:

This is the most effective and basic measure to prevent pressure drop.

Make a plan: According to the operating time of the air compressor station, the dust content in the environment, the oil content in the compressed air, and the filter life indicator of the pre-filter, make a detailed filter (including pre-filter, oil removal filter, and filter screen inside the cold dryer) inspection, cleaning and replacement cycle.

Quality assurance: When replacing the filter element, be sure to use the original or reliable quality compatible product to avoid using inferior filter elements to affect the filtering effect and pressure drop.

Drain valve inspection: Regularly check the working status of the automatic drain valve to ensure that it can smoothly discharge condensed water to prevent blockage and water accumulation. The drainage function can be tested manually, and the drain port and pipes can be cleaned.

Keep the condenser clean and dissipate heat well:

For air-cooled dryers, the heat dissipation effect of the condenser directly affects the high pressure of the refrigeration system.

Regular dust cleaning: Use compressed air or a soft brush to clean dust, oil, catkins and other debris on the condenser fins every week or month (depending on the dust in the environment). Be careful to avoid damaging the fins when cleaning.

Check the fan: Make sure the cooling fan blades are intact and not deformed, the motor runs smoothly and without abnormal noise, the speed is normal, and the airflow direction is correct. Lubricate the fan bearing regularly (if applicable).

Environmental requirements: Make sure there is enough heat dissipation space around the dryer to avoid the equipment being close to the wall or other obstacles. Keep the machine room well ventilated and the ambient temperature should not be too high (usually not more than 40°C), otherwise it will increase the condenser load.

Water-cooled condenser: For water-cooled dryers, check the water quality of the cooling water regularly to prevent scaling. Clean the condenser water side pipeline regularly to ensure that the cooling water flow and water pressure meet the requirements.

Regularly check the refrigerant status and system sealing:

Refrigerant is the lifeline of the refrigeration cycle.

Pressure and sight glass observation: In daily work, pay close attention to the high and low pressure gauge readings of the refrigeration system, and observe the refrigerant flow in combination with the sight glass (if any). Abnormal conditions should be recorded in time.

Regular leak detection: It is recommended to ask professionals to use professional leak detectors to conduct a comprehensive leak detection of the refrigeration system every year or every two years to eliminate minor leaks.

Timely replenishment/treatment: Once insufficient or leaking refrigerant is found, the leak point should be repaired immediately and the refrigerant should be accurately replenished according to the equipment requirements. Do not add it at will, overcharging will also cause high pressure problems.

Monitor and record operating parameters:

Establishing a comprehensive operating data recording system is the basis for predictive maintenance.

Key data: Record key parameters such as the inlet and outlet pressure, inlet and outlet temperature, exhaust dew point, high and low pressure of the refrigeration system, ambient temperature, and air compressor operating status of the dryer on a daily or weekly basis.

Trend analysis: By comparing historical data, potential abnormal trends can be found, such as the gradual increase in pressure difference, the slow increase in dew point, and the gradual deviation of high or low pressure from the normal range, so as to take intervention measures before the problem worsens.

Professional regular maintenance and care:

Many faults are difficult to be detected by non-professionals in the early stages.

Entrust professional services: It is recommended to conduct professional comprehensive inspection and maintenance provided by the original manufacturer or authorized service provider at least once a year. This usually includes: refrigeration system performance test, electrical component inspection, valve function inspection, safety protection device calibration, system internal cleaning, replacement of wearing parts, etc.

Troubleshooting: For complex faults inside the refrigeration system, such as refrigeration compressor failure, expansion valve failure, dry filter blockage, etc., it must be handed over to experienced professional refrigeration maintenance personnel for handling.

Optimize compressed air pipeline and system management:

Pipeline leak detection: Regularly check the entire compressed air pipeline system for leaks, repair all leaks in time, and ensure stable pressure transmission.

Reasonable selection and configuration: Ensure that the processing capacity of the refrigerated dryer matches the gas output of the air compressor and the actual needs of the downstream gas use point. Avoid situations where “overkill” or “a small horse pulling a big cart”.

Post-processing equipment maintenance: If there are other filters or dryers connected to the back of the dryer, they should also be included in the regular maintenance plan to ensure that they do not become new pressure loss points.

Conclusion

As an indispensable compressed air quality assurance equipment in industrial production, the stable operation of the refrigerated dryer is directly related to production efficiency, product quality and even the operating cost of the enterprise. Abnormal pressure is the most common “sub-health” state in its operation, and it is also an early signal of many potential faults. Through the in-depth analysis of this article, we understand that the main causes of abnormal pressure in the refrigerated dryer are: filter blockage, refrigeration system failure, and external pneumatic pipeline and valve problems.

Faced with these challenges, passive maintenance alone is far from enough. A set of scientific and forward-looking management and maintenance strategies is particularly important. From daily careful observation of instrument data to comprehensive sensory judgment; from regular cleaning and maintenance to in-depth inspection by professional technicians; from the maintenance of a single device to the optimization management of the entire compressed air system – every step is indispensable.

Investing in preventive maintenance of refrigerated dryers is not only to avoid downtime, but also a strategic investment in production continuity, product quality and energy efficiency. When your refrigerated dryer operates at its best, it will continuously deliver dry and clean compressed air, injecting stable and efficient power into your production line, thereby maximizing your industrial production benefits. Let us work together to ensure that every drop of compressed air is dry and pure, safeguarding the arteries of industry.