Atlas Copco Unloader Valve Kit Replacement – 2906095800

Atlas Copco 2906095800 – Unloader Valve Kit

The Atlas Copco 2906095800 (2906-0958-00) is an Unloader Valve Kit designed for compatible stationary oil-injected screw compressors, with Atlas Copco officially listing it for the GA90–GA160 range.

The unloader valve is a critical part of the compressor control system. It regulates the compressor’s operating condition by controlling the intake/unloading process, allowing the compressor to produce compressed air when required and reduce air production when the required system pressure has been reached.

Working Process:

During loaded operation, the compressor control system positions the unloader/inlet mechanism so that atmospheric air can enter the compressor element.

The screw compressor element compresses the incoming air and delivers the compressed air into the compressor’s air/oil separation system and subsequently toward the compressed-air outlet.

As downstream system pressure reaches the programmed unload pressure, the compressor controller activates the unloading circuit.

The unloader valve changes position and reduces the effective intake or compression process. This places the compressor into an unloaded condition and reduces unnecessary power consumption.

When compressed air is consumed by the downstream system, pressure gradually decreases.

Once the pressure reaches the programmed load point, the control system changes the unloader valve position back toward the loaded condition.

The compressor resumes normal air intake and compression.

This automatic load/unload cycle allows compressor operation to follow the actual compressed-air demand.

Main Functions:

• Controls compressor loading and unloading.
• Regulates the compressor inlet/control circuit.
• Helps maintain stable compressed-air system pressure.
• Reduces unnecessary compression during low-demand periods.
• Helps reduce power consumption during unloading.
• Maintains reliable pneumatic control of the compressor.
• Restores valve sealing and mechanical performance during maintenance.

Official Application:

Atlas Copco identifies 2906095800 for stationary oil-injected compressors / GA90–160. The official catalog lists a weight of 1.59 kg.

Official Component Breakdown:

Atlas Copco’s catalog lists the following components in the kit:

• Assembly – 1 pc
• O-ring – 1 pc
• O-ring – 1 pc
• Valve Solenoid – 1 pc
• M26 Washer – 1 pc
• Seal – 1 pc
• O-ring – 1 pc
• Tape – 1 pc
• O-ring – 1 pc
• Seal Lip – 1 pc
• Bearing – 1 pc
• BOV Assembly Kit – 1 pc
• Lock Washer – 1 pc
• O-ring – 1 pc
• Ball Bearing – 1 pc
• Seal – 1 pc
• C190 Unloader Kit Assembly Instructions – 1 pc

This component list is directly supported by Atlas Copco’s official product catalog.

The valve solenoid provides the electrically controlled actuation signal for the unloading system.

The assembly and BOV assembly kit form part of the valve/control mechanism responsible for changing the compressor between operating conditions.

The O-rings, seals and seal lip prevent leakage around the valve and control components.

The bearings and ball bearing support the relevant moving components and help maintain smooth mechanical operation.

The washers and locking washer secure components and help prevent loosening during compressor vibration.

The tape is part of the specified service-kit assembly and is installed according to the applicable service instructions.

Operating Cycle:

1. Start-up: The compressor control system places the unloader in its required starting position.
2. Loading: The unloader allows the compressor to enter normal air-production operation.
3. Air Compression: The screw element compresses incoming atmospheric air.
4. Pressure Build-up: System pressure increases.
5. Unload Command: At the programmed unload condition, the controller activates the unloading circuit.
6. Unloading: The valve changes position and reduces compressor air production.
7. Pressure Reduction: Downstream equipment consumes compressed air.
8. Load Command: When pressure reaches the load point, the controller commands the valve toward the loaded position.
9. Normal Operation: The compressor resumes air production.

The cycle repeats automatically according to compressed-air demand.

Role of the Solenoid Valve:

The solenoid valve provides controlled actuation of the pneumatic/mechanical unloading circuit.

When the compressor controller sends the appropriate electrical command, the solenoid changes the control-air path.

This pressure change acts on the unloader mechanism and causes the valve assembly to move toward the required loaded or unloaded position.

Reliable solenoid operation is therefore important for correct compressor load/unload response.

Importance of Sealing Components:

The O-rings and seals in the 2906095800 kit are essential for maintaining the required control pressure.

A damaged or hardened seal can allow control-air leakage.

Control-air leakage can prevent the unloader mechanism from receiving the correct pressure signal and may result in delayed, incomplete or incorrect unloading.

Replacing the sealing components during overhaul helps restore reliable valve operation.

Possible Failure Conditions:

With prolonged operation, the unloader valve can experience:

• O-ring deterioration
• Seal wear
• Solenoid malfunction
• Bearing wear
• Contamination
• Mechanical sticking
• Loss of control-air pressure
• Valve leakage
• Wear of moving components

If the unloader valve fails to unload, the compressor may remain loaded after reaching the required system pressure. This can increase power consumption.

If the valve fails to load correctly, compressed-air production may be reduced or the compressor may fail to build pressure normally.

A defective solenoid can prevent the valve from responding correctly to controller commands.

Damaged seals can cause control-air leakage and unstable operation.

Typical symptoms include:

• Compressor fails to load.
• Compressor fails to unload.
• Slow pressure build-up.
• Reduced air delivery.
• Compressor remains continuously loaded.
• Excessive power consumption.
• Unstable operating pressure.
• Delayed load/unload response.
• Air leakage.
• Valve sticking.
• Abnormal compressor cycling.

Maintenance Procedure:

Before servicing the unloader valve, the compressor must be stopped, electrically isolated, completely depressurized and allowed to cool according to the applicable Atlas Copco safety procedure.

The unloader assembly should be inspected for:

• Damaged O-rings
• Hardened or damaged seals
• Solenoid operation
• Bearing condition
• Mechanical wear
• Contamination
• Valve sticking
• Control-air leakage
• Damaged mating surfaces

Remove the worn components carefully without damaging the valve body or associated compressor components.

Install the components supplied in the 2906095800 Unloader Valve Kit according to the applicable Atlas Copco C190 unloader-kit assembly instructions.

All sealing surfaces should be thoroughly cleaned before assembly.

O-rings and seals must be installed without twisting, cutting, overstretching or pinching.

Bearings and moving components must be correctly positioned.

The solenoid valve must be correctly installed and electrically connected.

Fastening components and locking washers must be installed correctly.

After assembly, manually or mechanically verify that the unloader mechanism moves smoothly according to the applicable service procedure.

Restart the compressor and observe several complete load/unload cycles.

Verify:

• Correct loading.
• Correct unloading.
• Normal pressure build-up.
• Stable system pressure.
• Proper solenoid response.
• No abnormal control-air leakage.
• No valve sticking.
• No unusual mechanical noise.

A correctly serviced unloader valve ensures reliable compressor capacity control and allows the compressor to respond efficiently to changing air demand.

Using the Atlas Copco 2906095800 Unloader Valve Kit during the appropriate maintenance operation helps restore valve sealing, solenoid control, mechanical movement and reliable load/unload performance.

Part Number: 2906095800
Alternative Number: 2906-0958-00 / 2906 0958 00
Brand: Atlas Copco
Official Description: Unloader Valve Kit for Oil-Injected Screw Compressors
Application: Stationary oil-injected screw compressors
Known Application: GA90–GA160
Official Listed Weight: 1.59 kg
Component Type: Unloader Valve Service/Maintenance Kit
Primary Function: Controls compressor loading and unloading
Secondary Function: Regulates the compressor inlet/control circuit
Control Component: Valve solenoid
Main Components: Valve assembly, solenoid, O-rings, seals, bearings, BOV assembly kit, washers and related service components
Operating Function: Changes compressor operating condition according to the control signal and system pressure
Main Benefits: Reliable load/unload control, stable pressure, reduced unnecessary power consumption, improved sealing and dependable compressor operation.

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