ADR Series Hot Gas Bypass Valve – The Intelligent Solution for Stable Suction Pressure and Reliable Refrigerated Compressed Air Dryers

In a Refrigerated Compressed Air Dryer, the quality of compressed air depends not only on the refrigeration compressor, evaporator, condenser, or expansion valve, but also on the system's ability to maintain a stable suction pressure under varying load conditions.

One of the most critical components responsible for this function is the Hot Gas Bypass Valve (HGB Valve).

The ADR Series Hot Gas Bypass Valve is specifically engineered to regulate compressor suction pressure by bypassing hot discharge gas back to the suction line whenever the refrigeration load decreases. This intelligent control method ensures the refrigeration system continues operating within its optimum performance range, even under partial-load conditions.

Why Does a Refrigeration System Need a Hot Gas Bypass Valve?

In real industrial applications, compressed air demand is rarely constant.

Typical operating conditions include:

• Reduced production during night shifts
• Temporary shutdown of production lines
• Air compressors operating in Load/Unload mode
• Variable Speed Drive (VSD) compressors reducing airflow
• Compressed air consumption below design capacity

Under these conditions:

• Heat load entering the evaporator decreases.
• Refrigerant evaporates more slowly.
• Compressor suction pressure begins to drop.

Without proper suction pressure control, the refrigeration system may experience:

❌ Excessively low evaporating temperature

❌ Evaporator icing and frost formation

❌ Blocked airflow through the heat exchanger

❌ Insufficient refrigerant return to the compressor

❌ Poor oil return and inadequate compressor lubrication

❌ Compressor operation outside its designed operating envelope

❌ Reduced compressor reliability and shortened service life

These are among the most common causes of failure in refrigerated compressed air dryers operating under low-load conditions.

Operating Principle of the ADR Series Hot Gas Bypass Valve

The ADR Series is an Externally Equalized Hot Gas Bypass Regulating Valve.

Its operation is based on the balance between:

• Refrigeration system suction pressure
• Internal spring force

Normal Cooling Load

When the refrigeration load is sufficient:

• Suction pressure remains at its normal operating level.
• Refrigerant pressure overcomes the spring force.
• The valve remains fully closed.

The refrigerant follows the standard refrigeration cycle:

Compressor → Condenser → Expansion Valve → Evaporator → Compressor

Under these conditions, the refrigeration system delivers maximum cooling efficiency.

Low Cooling Load

When compressed air flow decreases:

• Heat load on the evaporator drops.
• Suction pressure decreases.
• The internal spring force overcomes the reduced suction pressure.

The ADR valve gradually opens.

A controlled portion of high-temperature, high-pressure discharge gas is redirected from the compressor discharge line directly into the suction line.

This creates an:

Artificial Refrigeration Load

also known as

Hot Gas Bypass Control.

As a result:

• Suction pressure increases to the preset value.
• Evaporating temperature remains stable.
• Evaporator icing is prevented.
• The refrigeration compressor continues operating safely and efficiently.

Why Does ADR Series Use an External Equalizer?

Unlike conventional regulating valves that sense pressure directly inside the valve body, the ADR Series incorporates a 1/4" ODF External Equalizer Connection.

This design offers several engineering advantages:

✔ Accurate measurement of the actual evaporator outlet pressure

✔ Compensation for pressure losses across the evaporator

✔ Faster response to changing system loads

✔ More precise suction pressure regulation

✔ Improved dew point stability

For these reasons, externally equalized hot gas bypass valves are widely used in medium and large industrial refrigerated air dryers.

Engineering Benefits of ADR Series

1. Stable Pressure Dew Point

Maintains a consistent pressure dew point between 3°C and 7°C, ensuring high-quality dry compressed air while preventing downstream condensation.

2. Prevents Evaporator Freeze-Up

When evaporating temperature falls below freezing, moisture condenses and freezes on the evaporator surface.

ADR Series maintains the evaporating temperature within a safe operating range, preventing ice formation.

3. Protects the Refrigeration Compressor

A refrigeration compressor requires:

• Stable refrigerant return
• Proper oil return
• Adequate suction pressure

The ADR Series continuously maintains these operating conditions, significantly extending compressor service life.

4. Reduces Compressor Cycling

The refrigeration compressor no longer needs to start and stop repeatedly during fluctuating load conditions.

Benefits include:

• Reduced starting current
• Lower electrical stress
• Improved energy efficiency
• Extended service life of contactors, relays, and compressors

5. Improves Overall Refrigeration System Reliability

A refrigeration system with stable suction pressure offers:

• Reduced vibration
• Lower thermal stress
• Fewer maintenance interventions
• Longer equipment life
• Improved operational stability

Technical Specifications

Compatible Refrigerants

• R22
• R134a
• R404A
• R507A

Valve Type

• Hot Gas Bypass Regulating Valve
• Externally Equalized

External Equalizer Connection

• 1/4" ODF

Primary Functions

• Compressor suction pressure regulation
• Hot gas bypass control
• Evaporator freeze protection
• Artificial refrigeration load control
• Stable pressure dew point maintenance

ADR Series Product Range

Hot Gas Bypass ADR Series

Typical Applications

The ADR Series Hot Gas Bypass Valve is widely used in:

• Refrigerated Compressed Air Dryers
• Air-Cooled Refrigeration Dryers
• Water-Cooled Refrigeration Dryers
• Industrial Chillers
• Cold Storage Systems
• Commercial Refrigeration Equipment
• HVAC Systems
• Process Cooling Applications

Hop Nhat HCM Compressor – Your Trusted Partner for Industrial Compressed Air Systems

Hop Nhat HCM Compressor Engineering Co., Ltd. specializes in supplying high-quality Hot Gas Bypass Valves, including KVC, KVL, KVR, and the complete ADR Series, suitable for replacement and OEM applications in a wide range of refrigerated compressed air dryers.

Beyond component supply, our experienced engineering team provides professional services including:

• Hot Gas Bypass Valve selection
• ODF and SAE connection matching
• Suction pressure adjustment and commissioning
• Refrigerated air dryer troubleshooting
• Preventive maintenance
• System retrofitting and performance optimization

Our mission is to help customers improve system reliability, reduce energy consumption, extend equipment life, and ensure a consistently stable compressed air dew point.

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