Kaeser Control Line Kit DN4/DN6 Replacement – 400998.0

Kaeser 400998.0 – Control Line Kit DN4/DN6

The Kaeser 400998.0 Control Line Kit DN4/DN6 is a pneumatic control-line service kit used in Kaeser rotary screw air compressors. Its primary function is to provide reliable small-bore tubing and connections for transmitting pneumatic control-pressure signals between the compressor’s 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 pressure signals from one control component to another, allowing the compressor control system to automatically respond to changes in discharge pressure and compressed-air demand.

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

Once the compressor reaches operating speed, the control system changes the pneumatic signal supplied to the inlet-control mechanism. The inlet valve can then open, allowing atmospheric air to enter the compressor air end for compression.

During loaded operation, the DN4/DN6 control lines continuously transmit pressure signals to the relevant valves and regulators. When system pressure changes, the pneumatic control components respond by adjusting the compressor’s operating condition.

When the required discharge pressure is reached, the control system changes the control pressure. The unloader or inlet-control mechanism responds by restricting the compressor’s air intake. This reduces the compression load and allows the compressor to operate in an unloaded condition, reducing unnecessary power consumption.

When compressed-air demand increases and system pressure falls, the control pressure changes again. The pneumatic actuator responds and the inlet system returns toward the loaded position, allowing the compressor to produce compressed air again.

The 400998.0 kit therefore acts as the pneumatic communication network for the compressor control system. It does not normally carry the main compressed-air flow; instead, it transfers the small control-pressure signals required for automatic valve and actuator operation.

Kaeser parts references identify 400998.0 as a Control Line Kit, while detailed trade and product records specifically describe it as “KIT CONTROL LINES DN4-DN6.”

The control tubing operates continuously under pressure fluctuations and is exposed to vibration, heat, oil mist, and mechanical movement. Over time, tubing can become brittle, cracked, kinked, abraded, or contaminated. Fittings and connection points may also loosen or develop leakage.

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

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

The replacement components supplied in the 400998.0 kit should be installed in their correct positions and routed according to the applicable Kaeser service procedure. Correct routing is important to prevent sharp bends, excessive vibration, abrasion, and contact with hot or moving compressor components.

After installation, the complete pneumatic 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 response.

A damaged or incorrectly connected control line can cause loss of control pressure and incorrect operation of connected valves. Correct replacement of the 400998.0 Control Line Kit restores reliable pneumatic signaling and helps maintain stable compressor operation.

Part Number: 400998.0
Brand: Kaeser
Part Description: Control Line Kit / Control Lines Kit DN4-DN6
Component Type: Pneumatic control-line service kit
Line Configuration: DN4/DN6
Application: Kaeser rotary screw air compressors
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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