KR20200017210A - Air supply for a pneumatic system of a commercial vehicle and method for operating an air supply unit - Google Patents

Abstract

The present invention relates to an air supply unit (2) for a pneumatic system of commercial vehicles. The air supply unit (2) can be operated in a supply mode and a restoration mode provided to supply compressed air (5) to an air supply unit inlet part (2a) of the air supply unit (2) to supply output pressure (p0) to a storage (16) and a consumption circuit (4), and to supply the air to an air supply unit discharge part (2b) through an air treatment unit (8) to remove moisture from the compressed air (5). In order to avoid the formation of oil-water emulsion in the air treatment unit (8), the restoration mode includes: a first purge step of starting the restoration step (II) and heating the air treatment unit (8); and a second purge step of removing moisture from the air treatment unit (8). The purge steps are implemented with an additional delay valve (24) provided to a signal discharge part to output an unloader signal (6) to a compressor (3).

Description

How to Operate Air Supply Units and Air Supply Units for Pneumatic Systems in Commercial Vehicles {AIR SUPPLY FOR A PNEUMATIC SYSTEM OF A COMMERCIA

The following invention relates generally to an air supply unit and a method of operating the air supply unit for a pneumatic system of a commercial vehicle.

The air supply systems of a commercial vehicle are provided in particular for the air supply of pneumatic systems such as pneumatic brakes, pneumatic suspension systems or pneumatic auxiliary devices in commercial vehicles.

The air supply system generally includes a compressor driven by a motor of a vehicle, an air treatment unit including an air dryer with an air drying agent (drying agent), a valve unit and an electronic control unit (ECU). This air supply system can be operated in various modes of operation, which is initiated by an electronic control unit which outputs electronic signals to the electro-pneumatic valves of the valve arrangement. These various modes of operation are especially:

In the supply mode, the air is sucked from the compressor or the external environment and the compressed air is supplied to the air treatment unit, where the compressed air is treated (dry and filtered); The treated air is then delivered to an air consumption circuit and an air tank for storing a portion of the treated air, where the air tank may be provided separately from or as part of the air consumption circuit.

In regeneration mode (purge mode), the treated air stored in the air tank is fed back through the air treatment unit to dry (dehumidify) the drying agent or desiccant in the air treatment unit and the air of the air treatment unit It is discharged by an air vent (discharge vent). In this regeneration mode the compressor is switched off by a pneumatic unloader (control) signal output from the air processing unit to the unloader port of the compressor via a pneumatic control line.

'Switch off' or deactivation of the compressor is implemented, for example, by a compressor clutch provided in or on the motor shaft, or by switching the compressor from its operating state to an idle state with no or no negligible air output. Can be.

In the feed mode engine oil and other components can be aspirated by the compressor and output to the air treatment unit. In the off state of the compressor, moisture tends to condense in the air control line while passing through the air discharge line. Moisture condensed inside the pneumatic control line and certain types of engine oil continually form an oil-water mixture, an emulsion, which accumulates in the connected pipelines and air treatment cartridges of the air dryer, which leads to poor air quality and frequent It may cause a charging error. This emulsion has a viscous 'mayonnaise' concentration and can render the air treatment unit unusable.

It is therefore an object of the present invention to provide an air supply unit and a method for operating the air supply unit that can prevent or reduce the production of an oil-water emulsion with minimal effort.

According to one aspect of the invention, an air supply unit according to claim 1 is provided.

According to a second aspect of the invention, a method of operating an air supply unit according to claim 10 is provided.

The present invention is based on the idea of providing additional heating of the air treatment unit by operating the compressor even after the supply mode. Therefore, the conventional regeneration step or purge step according to the prior art in which the compressor supply is stopped and the regeneration air flow from the air supply unit outlet through the purge valve assembly to the vent outlet is started. After the feed mode a first purge stage (regeneration stage) is started, where the compressor is still running and supplying compressed air, which is then delivered to the vent outlet of the air supply unit, thereby heating the air treatment unit. To flow or flow along the air treatment unit. Compressed air is generally relatively hot and can therefore be used to heat or 'bake out' the air treatment unit to prevent or reduce any oil-water emulsion from the air treatment unit. . The first regeneration step is then converted to a second purge step (regeneration step), in which the compressor is stopped and regeneration air can flow through the purge valve assembly, the air treatment unit and into the vent outlet of the air supply unit. Similar or identical to the traditional regeneration step.

The transition from the supply mode to the first purge stage is preferably dependent on the output pressure. That is, it is pressure-controlled: when the pressure top reaches or exceeds the pressure threshold, the first purge valve (or control purge valve) of the purge valve assembly is switched, thereby switching the purge relay valve in series with the throttle. . Since the compressor is still running and providing air flow of compressed air, the regeneration air flow in this first purge step is relatively small, which results in higher pressure at the inlet of the air treatment unit. However, the output pressure is lowered by this small regeneration air flow in the first purge step.

The delay of the second purge step is realized by a delay valve provided between the signal valve and the signal outlet for delivering the pneumatic unloader signal. The delay valve is preferably controlled by several factors, in particular a spring bias and two reaction pneumatic control inputs to ensure a basic shut off position. These factors or forces acting on each other keep the delay valve in its primary shut-off position in the first purge step and switch to its active open position in the second purge step. The two reactive pneumatic control inputs are preferably output from the pressure and signal valves, in particular between the purge relay valve and the throttle, in the regeneration valve assembly.

The air supply unit and method according to the invention thus provide several advantages:

Further heating of the air treatment unit can be implemented to prevent the formation of an oil-air emulsion. No other heating devices are needed since the heat supply can be realized with compressed air delivered by the compressor. Since the first purge step immediately follows the supply mode, there is no need to stop the compressor after the supply mode.

Since air consumption affects the output pressure, taking into account air consumption in these steps, switching between steps can be implemented with pressure control, thereby ensuring the defined steps.

The additional hardware equipment is relatively small, in particular having only additional delay valves, which can be implemented by a plunger device integrated into the housing of the air supply unit.

The invention is explained in detail below with reference to the accompanying drawings.

1 is a configuration diagram of a pneumatic system including an air supply unit according to an embodiment of the present invention.
2 is a cross-sectional view of the delay valve in the first position.
3 is a cross-sectional view of the delay valve in a second position.
4 is a cross-sectional view of a regeneration valve including a throttle.
5 is a cutaway perspective view of a hardware implementation in accordance with one embodiment including portions of a purge valve assembly.
6 is a flowchart of a method according to an embodiment of the present invention.

1 shows a pneumatic configuration diagram of a pneumatic system 1 of a commercial vehicle such as a truck. The pneumatic system 1 comprises an air supply unit (ASU) 2, a compressor 3 and consumption circuits 4, shown in dashed lines. The compressor 3 is in particular driven by a motor engine and supplies compressed air 5 to the air supply unit inlet 2a of the air supply unit 2. The compressor 3 can be switched off by the pneumatic unloader signal 6 input to its unloader port (pneumatic control input) 3a. In this 'switched off' state, the compressor 3 is switched off completely or switched to an idle state without supply of compressed air 5.

The air supply unit 2 comprises an air processing unit (APU) 8 having a filter 9 and a desiccant cartridge 10. The APU input 8a is connected to the air supply unit inlet 2a by the inlet line 12. The APU outlet 8b is connected to a non-return valve (separating valve) via the first output line 13; The check valve (separation valve) 14 is connected to an air supply unit outlet (ASU outlet) 2b by a second output line 15. Several consumer circuits 4, such as pneumatic brake systems, suspension systems and other pneumatic consumers, can be connected to the ASU outlet 2b. A reservoir 16 is connected to the ASU outlet 2b, which may be provided separately or as part of the consumption circuits 4. The reservoir 16 may in particular be embodied as part of a 'gallery line' connecting the separate consumption circuits.

In supply mode I, the compressor 3 is driven by a running vehicle engine and supplies compressed air 5 to the ASU inlet 2a, which passes through the inlet line 12 and the APU. ASU outlet 2b from the APU outlet 8b through the first output line 13, the separation valve 14 and the second output line 15 through the APU 8 and supplied to the inlet 8a. Is supplied. The output pressure p0 is then stored in the reservoir 16 at the ASU outlet 2b; This output pressure p0 is generally dependent on the operating time of the compressor 3 and the air consumption by the consumption circuits 4.

The air supply unit 2 further includes a purge valve assembly 18 provided for implementing regeneration mode II (purge mode) for dehumidifying (dehumidifying) the desiccant cartridge 10 of the APU 8. In this embodiment, the purge valve assembly 18 is a vent valve device 19 for bypassing the check valve (separation valve) 14 in regeneration mode II, a vent for outputting the pneumatic unloader signal 6. Valve 20, signal valve 22 and delay valve 24.

The bypass valve device 19 comprises a first purge valve 26 implemented as a pneumatically controlled valve, which purge valve 26 shuts off in its basic position and at its input 26a output pressure. It opens when (p0) reaches or exceeds the purge pressure threshold (pt26), for example 12 bar. The first purge valve 26 pneumatically controls a purge relay valve 27 having a throttle 28 and connecting a second output line 15, which throttle 28 is the first output line 13. It is connected to, and through it is connected to the APU outlet (8b). In addition, a delay signal line 31 is connected to the purge line 127, which extends between the purge relay valve 27 and the throttle 28.

The delay valve 24 is configured as a 3 / 2-valve including a delay valve input 24d, a delay valve output 24e connected to the unloader output 2d, a vent discharge 24f and specific pressure control. The delay valve 24 includes a first pneumatic control input 24a and a spring bias 24c that act in response to the second control input 24b. In the absence of pressure control, the spring bias 24c ensures the shutoff basic position, where the delay valve input 24d is shut off and the delay valve output 24e is vented by the vent outlet 24f; Thus no unloader signal 6 is transmitted.

The vent valve 20 is switched between the APU inlet 8a and the vent outlet 2c of the ASU 2, where the vent valve 20 is the first pneumatic control input 20a and the second pneumatic control input. (20b). In its biased base position, the vent valve 20 is shut off. Even if the compressor 2 is in operation and pressurizes the inlet line 12 acting on the first pneumatic control input 20a, the vent valve 20 remains in its shutoff basic position. The vent valve 20 can only be switched when an additional pneumatic pressure acts on the second pneumatic control input 20b.

The signal valve 22 is switched between the ASU outlet 2b and the unloader signal line 32, which is the first control input 24a of the delay valve 24 and the delay valve. It is connected to the input part 24d. The signal valve 22 is implemented as a 3 / 2-valve biased to its blocking base position for venting the unloader signal line 32. The signal valve 22 is pneumatically controlled by the output pressure p0 and opens when the output pressure p0 reaches the unloader pressure threshold pt22 at its control input 22a. In the activated position, the signal valve 22 is opened to connect the ASU outlet 2b with the unloader signal line 32, through which the first control of the delay valve 24 is carried out, as described in detail below. It is connected to the input part 24a and the 2nd pneumatic control input part 20b.

When the output pressure p0 reaches a purge pressure threshold pt26 of, for example, 12 bar, the first purge valve 26 opens and thus switches the purge relay valve 27; The output pressure p0 then flows through the purge relay valve 27 and the throttle 28 to the APU outlet 8b, thereby bypassing the separation valve 14. In addition, the delay signal line 31 is pressurized by the output pressure p0 and acts on the second control input 24b of the delay valve 24, thereby ensuring the basic position of the delay valve 24. Thus compressor 3 is still in operation; The vent valve 20 is still blocking and thus compressed air is still supplied to the ASU output 2b via the isolation valve 14, thereby increasing the output pressure p0. In this situation, no purge air can circumvent the separation valve 14 through the purge valve device 19.

The signal valve 22 opens when the output pressure p0 exceeds the unloader pressure threshold pt22, which is preferably higher than the purge pressure threshold pt26. When the signal valve 22 is opened, the unloader signal line 32 acting on the first control input 24a of the delay valve 24 is pressed. However, the combined force of the spring bias 24c and the output pressure p0 acting on the second control input 24b is higher than the corresponding force exerted by the output pressure p0 acting on the first control input 24a. Thus, the delay valve 24 is kept in its basic position and no unloader signal 6 is output to the unloader port 3a of the compressor 3.

In this situation, the combined pressure forces acting on the first pneumatic control input 20a and the second pneumatic control input 20b overcome the spring bias of the vent valve 20 and move the vent valve 20 to the activated open position. In this case, the inlet line 12 is connected to the vent outlet 2c.

Thus a first purge stage IIa of regeneration mode II is implemented, in which the compressor 3 is still in operation and supplies compressed air 5 to the input line 12. This compressed air 5 can exit through the open vent valve 20 and the vent outlet 2c; Thus no associated pressure is acting on the APU inlet 8a. The output pressure p0 passes through the open purge relay valve 27 and the throttle 28, flows to the outlet 8b of the APU 8, then passes through the APU 8 and the APU 8. Flows into the inlet section 8a and through the open vent valve 20 to the vent outlet section 2c, thereby regenerating the APU 8. The output pressure p0 is thus lowered by this steady flow, which is limited by the throttle 28.

Hot compressed air 5 from the inlet line 12 flowing along the APU 8 is thermally coupled to the APU 8 and contributes to heating the APU 8. Thus, in the first purge step IIa, two effects can be realized: the desiccant cartridge 10 of the APU 8 is regenerated by purge air flowing through the throttle 28, and the APU 8 is also operated. It is heated (or 'baked out') by the hot compressed air 5 supplied by the compressor 3 in operation.

The purge air flowing from the reservoir 16 through the ASU outlet 2b and the purge valve device 18 is stored in the reservoir 16 until the output pressure p0 reaches the delay pressure threshold pt_24. Lower the pressure p0. This time difference is defined by the throttle 28 until pt_24 is reached. That is, it is controlled by the pressure difference. In this situation, the force acting on the second pneumatic control input 24b combined with the force of the spring bias 24c is exerted by the pressure acting on the first control input 24a of the delay valve 24. Falling further down, it diverts the delay valve 24 to its open position. The unloader signal 6 is thus output to the unloader port 3a of the compressor 3 and switches off the compressor 3 or switches to its idle state.

In this situation a second purge step IIb is implemented, in which the compressor 3 does not provide compressed air 5 to the inlet line 12. Regeneration air still passes through the bypass valve arrangement 19, ie the valves 26, 27 and the throttle 28, and then the APU outlet 8b, APU 8 and APU inlet 8a. It passes and flows through the vent valve 20 to the vent discharge part 2c. The output pressure p0 acting on the second control input 20b of the vent valve 20 is sufficient to keep the vent valve 20 in its open position without assistance by the first control input 20a. This second purge step IIb thus enables a 'classic' purge flow for regenerating the APU 8 without driving the compressor 3.

When the falling output pressure p0 falls below the lower pressure threshold of the signal valve 22, it returns to its blocking base position, thereby venting the unloader signal line 32. Thus, the pressure at the first pneumatic control input 24a of the delay valve 24 drops, and the delay valve 24 is switched to its shutoff basic position and stops the transmission of the unloader signal 6. The compressor 3 thus starts delivering compressed air 5, which is the beginning of the next supply mode I.

2-5 depict a hardware implementation of this valve arrangement in casing 130, where FIGS. 2 and 3 show two positions of delay valve 24. According to FIGS. 2 and 3, the delay valve 24 is implemented in the casing 130 by a plunger 124 inserted in the gap 131 of the casing 130.

In the basic position of FIG. 2, the delay valve output 24e is connected to the vent outlet 24f; The delay valve input portion 24d is blocked by the position of the plunger 124. As can be seen in FIG. 2, the port serving as the delay valve input 24d acts on the bottom surface 124a of the plunger 124; As a result, the first pneumatic control input unit 24a is implemented. Thus, in the hardware implementation of FIGS. 2 and 3, the delay valve input 24d and the first pneumatic control input 24a are implemented by one port. Thus, the pressure in the unloader signal line 32 is increased by switching the signal valve 22, and the pressure at the delay valve input 24d and the first pneumatic control input 24a is increased; However, as long as the pressure at the second pneumatic control input 24b is sufficiently high, it is applied by the pressure at the spring bias 24c and the second pneumatic control input 24b acting on the top surface 124b of the plunger 124. The sum of the losing forces is greater than the force exerted by the pressure at the first pneumatic control input 24a.

In FIG. 3, the pressure at the second pneumatic control input 24b drops, so that the pressure acting on the first pressure control input 24a moves the plunger 124a upward to the activated position of FIG. 3. High enough. The delay valve 24 is thus in its activated position, where the delay valve input 24d is connected to the delay valve output 24e and the vent outlet 24f is blocked.

4 and 5 illustrate a hardware implementation, in which the delay valve 24 as well as the throttle 28 and the unloader signal line 31 are provided with a casing 130 and an additional connection element 132 sealed. It is implemented in the casing 130 by. The throttle 28 is implemented by an orifice or bore with a small cross section in the connecting element 132. Delay signal line 31 is implemented by passage 31a of connecting element 132 and bore 31b in casing 130.

6

Supply Mode I,

First purge step IIa,

Second purge step IIb

It describes the stages of

1 pneumatic system
2 air supply unit (ASU)
2a air supply unit inlet
2b air supply unit outlet
2c vent outlet
2d signal outlet
3 compressor
3a unloader port, pneumatic control input
4 consumption circuit
5 compressed air
6 pneumatic unloader signal
8 air handling units
8a APU Inlet
8b APU outlet
9 filters
10 desiccant cartridges
12 incoming lines
13 first output line
14 check valve (check valve, disconnect valve)
15 second output line
16 storage
Purge valve assembly comprising 18 components 19, 20, 22, 24
19 bypass valve unit
20 vent valve
20a first pneumatic control input
20b 2nd Pneumatic Control Input
20c vent valve inlet
20d vent valve outlet
22 signal valve
Control input of 22a signal valve 22
23 connection line between the second output line 15 and the signal valve
24 delay valve
24a first pneumatic control input
24b second pneumatic control input
24c spring bias
24d delay valve input
24e delay valve output
Vent outlet of the 24f delay valve (24)
26 1st Purge Valve
27 purge relay valve
27a purge relay valve inlet
27b purge relay valve outlet
27c purge relay valve control unit
28 throttle
31 delay signal lines
31a passageway within the connection element
Bore in 31b Casing 130
32 unloader signal lines
124 plunger
Bottom surface of 124a plunger 124
Top surface of 124b plunger 124
127 purge line
130 casing
Connecting element in 132 casing 130
p0 output pressure
pt26 purge pressure threshold
pt22 unloader pressure threshold
pt_24 delay pressure threshold
I supply mode
II playback mode
IIa first purge step
IIb Second Purge Step

Claims (13)

As an air supply unit 2 for a pneumatic system 1 of a commercial vehicle, the air supply unit 2 is:
An air supply unit inlet 2a connected to the compressor 3 for receiving compressed air 5,
An air supply unit outlet 2b connected to at least one consumption circuit 4 for delivering an output pressure p0,
A signal outlet 2d for outputting an unloader signal 6 for switching off the compressor 3,
An air treatment unit 8 for removing moisture in the compressed air 5 in the supply mode I,
A purge for implementing a regeneration mode (II) in which compressed air passes from the air supply unit outlet (2b) through the air treatment unit (8) to the vent outlet (2c) of the air supply unit (2). Valve assembly 18,
Including,
The purge valve assembly 18 includes a signal valve 22 which is pneumatically controlled by the output pressure p0,
The regeneration mode II includes a first purge step IIa without transmission of the unloader signal 6 and a second purge step IIb with transmission of the unloader signal 6,
A delay valve 24 is provided between the signal valve 22 and the signal outlet 2d to block or delay transmission of the unloader signal 6 in the first purge step IIa. Air supply unit (2). The method of claim 1, wherein the delay valve 24
A delay valve input 24d connected to the signal valve 22,
A delay valve output 24a and a first pneumatic control input 24d connected to the signal outlet 2d,
A spring bias 24c for biasing the delay valve 24 to its basic position where the signal outlet 2d is vented and no unloader signal 6 is transmitted, and
A second pneumatic control input 24b connected to the delay signal line 31 of the purge valve assembly 18.
Including,
The second pneumatic control input 24b acts to ensure the basic position of the delay valve 24, and the first pneumatic control input 24a moves the delay valve 24 to its activated open position. An air supply unit 2 acting to switch. 3. The purge valve assembly 18 of claim 2 wherein:
A first purge valve 26 connected to the air supply unit output 2b and controlled by the output pressure p0 of the air supply unit output 2b,
A purge relay valve 27 controlled by the first purge valve 26 and connected to the air supply unit output 2b,
Throttle (28) to lower air flow
Including,
The throttle 28 and the purge relay valve 27 are connected by a purge line 127, and the air supply unit output 2b and the air treatment unit discharge part (2) to bypass the check valve 14. 8b) in series,
The second pneumatic control input (24b) of the delay valve (24) is connected to the purge line (127) and is controlled by the purge line (127). 4. The purge valve assembly (18) according to claim 3, wherein the purge valve assembly (18) comprises a connecting element (132) comprising an orifice for implementing the throttle (28),
The connecting element (132) and the delay valve (24) are implemented in a common casing (130) and are connected via a bore (31b) for implementing the delay signal line (31). 5. The delay valve 24 is provided displaceably and biased to a basic position by the spring bias 24c.
The first pneumatic input 24a and the delay valve input 24d are implemented by a common spacing acting on the first face 124a of the plunger 124 with respect to the spring bias 24c,
The second pneumatic control input (24b) acts on the second surface (124b) of the plunger (124) facing the first surface (124a). Air supply unit (2) according to any one of the preceding claims, wherein the delay valve (24) is embodied as a 3 / 2-valve. The purge valve assembly 18 further comprises a vent valve 20.
The vent valve 20 is switched between the inlet line 12 and the vent outlet 2c extending between the air supply unit inlet 2a and the air treatment unit 8,
The vent valve 20 is biased to a shutoff basic position and controlled by a first pneumatic control input 20a connected to the inlet line 12 and a second pneumatic control input 20b connected to the signal valve 22. ,
The vent valve 20 is switched to its activated open position to vent the input line 12 when both pneumatic control inputs 20a, 20b of the vent valve 20 are pressurized,
The vent valve 20 does not switch to its open position when only the first control input 20a is pressurized. 8. The common unloader signal line of claim 7, wherein the second control input (20b) of the vent valve (20) and the delay valve input (24d) of the delay valve (24) extend from the signal valve (22). Air supply unit (2) connected to (32). The method of claim 1, wherein the supply mode (I) and the purge steps (I, II) are:
The supply mode (I) provides compressed air (5) to the air supply unit inlet (2a) and the air to supply the output pressure (p0) to the consumption circuits (4) and the reservoir (16). Is provided for passing through the processing unit 8 to the air supply unit discharge part 2b,
The second purge step IIa is provided for initiating the regeneration step II and for heating the air treatment unit 8,
The second purge step IIb is provided for removing moisture in the air treatment unit 8
Air supply unit 2 implemented in sequence. As the operation method of the air supply unit 2:
The compressor 3 passes through the air treatment unit 8 to remove moisture of the compressed air 5 through the air supply unit inlet 2a and into the air supply unit outlet 2b for the compressed air 5. Supply mode through which the output pressure p0 is transmitted to the connected consumption circuits 4 and the reservoir 16 for storing the output pressure p0,
Following the supply mode I, in the first purge step IIa the compressor 3 is still in operation and is supplying compressed air 5 to the air supply unit inlet 2a and the first purge In step IIa the vent valve 20 is switched to its open position for venting the inlet line 12 to the vent outlet 2c of the air supply unit 2, by means of the compressor 3. The compressed air 5 to be supplied is delivered to the vent outlet 2c via the open vent valve 20, through which the compressed air 5 flowing along the air supply unit 8 flows. A first purge step IIa for heating the air treatment unit 8,
Following the first purge step IIa, in the second purge step IIb, the compressor 3 is switched off by the pneumatic unloader signal 6 transmitted by the air supply unit 2, The vent valve 20 is still open and passes through the purge valve assembly 18, the air treatment unit 8, and the vent valve 20 from the air supply unit outlet 2b. Second purge step IIb, in which a regeneration air stream to 2c) is implemented to remove moisture from the air treatment unit 8
Air supply unit (2) operating method comprising a. 11. The method of claim 10, wherein the transition from the supply mode (I) to the first purge step (IIa) is controlled by a first purge valve (26) of the purge valve assembly (18). 26 is opened when the output pressure p0 falls below the purge pressure threshold pt26, thereby switching the purge relay valve 27 to its open position, thereby through the air supply unit outlet 2b. A method of operating the air supply unit (2) through the purge relay valve (27) and the throttle (28) to start the regeneration air flow to the air treatment unit (8). 12. A method according to claim 11, wherein the switching from said first purge step (IIa) to said second purge step (IIb) is implemented by pressure control in accordance with said output pressure (p0). 13. The method of claim 12, wherein the output pressure (p0) controls the delay valve (24) and holds the delay valve (24) in its shutoff basic position,
Switching from the first purge step IIa to the second purge step IIb causes the output pressure p0 to fall below the delay pressure threshold pt_24, thereby stopping the supply of compressed air 5. Air supply unit implemented to enable switching of the delay valve 24 to its open position for transferring the pneumatic unloader signal 6 to the unloader port 3a of the compressor 3 for (2) the method of operation.

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