Kaeser Control Line Kit DN4 Replacement – 400904.0

Kaeser 400904.0 – Control Line Kit DN4

The Kaeser 400904.0 Control Line Kit DN4 is a pneumatic control-line service kit used in Kaeser rotary screw air compressors. Its primary function is to provide reliable connections for the small-bore control-air lines that transmit pneumatic pressure signals between the compressor’s control valves, regulators, pressure-sensing devices, and actuators.

Working Process:

During compressor operation, compressed air is used as a control medium for various pneumatic components. The control lines carry these pressure signals from one control component to another, allowing the compressor to automatically respond to changes in operating pressure and load demand.

During start-up, the pneumatic control circuit establishes the required control pressure. These signals operate the compressor’s inlet and unloading mechanisms so that the compressor can start with reduced load.

Once the compressor reaches operating speed, the control system changes the pneumatic signal to allow the inlet system to open. Atmospheric air can then enter the screw element, where it is compressed and delivered to the downstream air system.

During loaded operation, the control lines continuously transmit pressure signals to the relevant valves and regulators. When system pressure changes, these signals cause the pneumatic control components to adjust the compressor’s operating condition.

When the required discharge pressure is reached, the controller changes the control pressure. The unloader/inlet-control mechanism responds by restricting the compressor’s air intake. This places the compressor into an unloaded condition and reduces the compression load and associated power consumption.

When compressed-air demand increases and system pressure falls, the pneumatic control signal changes again, allowing the compressor to return to loaded operation.

The 400904.0 Control Line Kit therefore acts as the reliable pneumatic communication path within the compressor control system. It does not normally compress or regulate the main air flow itself; instead, it transfers the control pressure signals required for automatic valve and actuator operation.

Kaeser parts references identify 400904.0 as a Control Line Kit, while supplier documentation specifically describes it as “KIT Steuerleitungen DN4” (Control Lines Kit DN4).

The control lines operate under continuous pressure fluctuations and are exposed to compressor vibration, heat, oil mist, and mechanical movement. Over time, tubing can become brittle, cracked, kinked, contaminated, or damaged. Fittings and connection points can also develop leakage.

A leaking control line can reduce or completely interrupt the pneumatic pressure signal reaching a valve or actuator. This may result in delayed loading, failure to unload, unstable pressure control, incorrect valve operation, or increased energy consumption.

During maintenance, the compressor should be stopped, isolated, and completely depressurized before the control-line system is serviced. Existing tubing and fittings should be inspected for cracks, abrasion, kinks, loose connections, contamination, and air leakage.

The replacement components supplied in the 400904.0 kit should be installed in their correct positions and routed according to the applicable Kaeser service procedure. Correct routing is important to prevent excessive bending, vibration, abrasion, and contact with hot or moving components.

After installation, the complete control circuit should be checked for leakage. The compressor should then be operated through its start-up, loading, unloading, and shutdown sequences to verify correct pneumatic control.

A damaged control line can cause loss of control pressure and incorrect operation of connected valves. Correct replacement of the 400904.0 Control Line Kit restores reliable pneumatic signaling and helps maintain stable compressor operation.

Part Number: 400904.0
Brand: Kaeser
Part Description: Control Line Kit / Kit Control Lines DN4
Component Type: Pneumatic control-line service kit
Application: Kaeser rotary screw air compressors
Line Size Reference: DN4
Primary Function: Transmits pneumatic control-pressure signals between compressor control components
Operating Function: Supports inlet control, unloading, pressure regulation, and pneumatic actuator operation
Main Benefits: Reliable control signaling, accurate valve actuation, stable load/unload operation, reduced control-air leakage, and dependable compressor performance.

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