JPH02560B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a capacity control device for an oil-free rotary compressor such as an oil-free screw compressor.

[Conventional technology]

The conventional system was a capacity control device described in Japanese Patent Application Laid-Open No. 59-93988. In this method, the diameter of the air discharge piping was adjusted to keep the discharge pressure constant during unloading. For this reason, the air release time was long, and the drop in the discharge pressure was particularly slow immediately after unloading, which caused the temperature of the discharge air to instantaneously rise by about 30°C.

[Problem to be solved by the invention]

In the above-described conventional technology, the temperature of the discharged air immediately after unloading becomes abnormally high as described above, causing the rotor and casing to locally expand and causing contact between the rotor and the casing.

The idea described in Utility Application No. 59-137625 is that a plurality of solenoid valves for blowing air are arranged in parallel with each other in the escape path of a lubricated compressor, and the pressure of the compressed air is This disclosure discloses a technique for rapidly reducing the pressure of discharged air to a predetermined pressure by controlling the opening/closing mode of the electromagnetic valve in at least two stages. However, the problem with this invention is to reduce the power during no-load operation, and to reduce the discharge pressure for this purpose, contact between the rotor and the casing due to the sudden rise in discharge air temperature, which is a problem in oilless compressors. There is no mention of any dangers.

An object of the present invention is to shorten the air release time when switching from loading to unloading to prevent the temperature of the discharged air from rising and to prevent the rotors from coming into contact with each other.

[Means to solve the problem]

The above-mentioned problems include: an air release valve that is opened at no load in conjunction with a suction throttle valve; an air release pipe that connects the discharge pipe between the compressor and the check valve and the inlet side of the air release valve; A capacity control device for an oil-free rotary compressor is equipped with an air release solenoid valve that is branched and connected to the air release pipe and opens the outlet side to the atmosphere, and a air release solenoid valve that opens the outlet side to the atmosphere for a predetermined period of time when switching to unloader operation. and timer means for opening the solenoid valve.

[Effect]

When switching to unload operation, the air release valve is opened, and at the same time, an air release solenoid valve provided in addition to the air release valve is opened for a predetermined time by a timer means.

Both the air release valve and the air release solenoid valve are connected to the discharge pipe between the compressor and the check valve, and when both are opened, the air in the pipe is rapidly released to the atmosphere.
Since the pressure within the pipe drops rapidly, even if the pressure on the suction side drops rapidly as the suction throttle valve closes, a sudden rise in the compression ratio can be avoided. Since there is no increase in the compression ratio, the discharge air temperature also does not increase.

〔Example〕

One embodiment of the present invention will be described below with reference to FIGS. 1 and 2.
This will be explained with reference to FIG.

Air to be compressed is sucked in through a suction port 1 and enters a compressor 3 via a suction throttle valve 2. Compressor 3
The air pressurized to a predetermined pressure is discharged from the discharge pipe 13 via the precooler 4, check valve 5, and aftercooler 6. When the amount of compressed air used decreases, the pressure in the discharge pipe 13 increases. This pressure is detected by the pressure switch 7, and the three-way solenoid valves 8 and 9 are switched based on this detection signal.
Operation air is sent to chamber B of the suction throttle valve 2. This operating air completely closes the unloader valve 15 and starts the unloading operation. The air release valve 14 opens in conjunction with this unloader valve 15, and the compressor 3
The discharged air between the check valve and the check valve is discharged to the atmosphere via the discharge pipe 12, and the discharge pressure is reduced to 1.5Kg/cmg.

Unloader valve 15 is closed and air release valve 14
At the same time that the air discharge solenoid valve 11 is opened, the air discharge solenoid valve 11 is opened for about two seconds, air is also discharged from the air discharge electromagnetic valve, and the pressure of the discharged air is rapidly reduced.

During unloading, the suction side of the compressor 3 is closed, so the suction side of the compressor 3 becomes a vacuum, resulting in a negative pressure of -500 mmHg. Compression of air by a compressor can be considered as adiabatic compression, and in the case of adiabatic compression, the higher the compression ratio, the higher the temperature of the compressed air. Therefore, when the discharge is delayed and the suction side of the compressor 3 reaches a negative pressure of -500 mmHg, if there is residual pressure in the discharge pipe between the compressor and the check valve 5, the pressure on the suction side will decrease. As the compression ratio increases, the temperature of the discharged gas increases rapidly as shown by the dotted line in FIG.

In this embodiment, in order to deal with this, the discharge solenoid valve 1
1 to the exhaust pipe 12, and this exhaust solenoid valve 11
is linked to the unloading operation, and the air is released together with the air release valve 14 for about 2 seconds after the start of the unloading operation, thereby shortening the time required to complete the air release.
It was possible to avoid a sudden increase in the compression ratio during unloading transients, and prevent an abnormal rise in the discharge gas temperature due to an increase in the compression ratio. As a result, the discharge temperature does not rise abnormally as shown by the solid line in FIG. 3, and troubles such as rotor contact due to thermal expansion caused by the abnormal rise in temperature can be prevented.

Next, according to the sequence shown in Fig. 2, the discharge solenoid valve 11 is
and the operation of the timer means will be explained.

When the pressure in the discharge pipe increases, the unloading pressure switch 7 opens, the auxiliary relay 16 becomes de-energized, the B contact of the auxiliary relay 16 short-circuits, and the timer 17 is set. As a result, while this timer is held, the discharge solenoid valve is opened and the discharge pressure is discharged.

In FIG. 1, solid line arrows indicate the flow during loading operation, dotted line arrows indicate the flow during unloading operation, and dashed-dotted line arrows indicate the flow during startup.

〔Effect of the invention〕

As described above, according to the present invention, when switching from loading to unloading of an oil-free screw compressor, there is provided an air release solenoid valve that is opened for a certain period of time to release air at the same time as unloading starts. Therefore, it is possible to prevent a sudden rise in discharge temperature immediately after unloading, and there is an effect of improving the reliability of the compressor by preventing rotor contact accidents due to thermal expansion caused by temperature rise.

[Brief explanation of drawings]

FIG. 1 is a flow sheet of an embodiment of the present invention;
FIG. 2 is a sequence diagram illustrating the operation of the discharge solenoid valve, and FIG. 3 is a diagram showing the relationship between discharge air temperature and time when switching from loading operation to unloading operation. 1... Suction port, 2... Suction throttle valve, 3... Compressor, 4... Pre-cooler, 5... Check valve, 6... After cooler, 7... Pressure switch, 8... Three-way solenoid valve, 9... Three-way solenoid valve, 10... Three-way solenoid valve, 11... Discharge solenoid valve, 12... Discharge piping, 1
3...Discharge pipe, 14...Air discharge valve, 15...Unloader valve, 16...Auxiliary relay, 17...Timer.

Claims (1)

[Claims] 1 An air release valve that is opened at no load in conjunction with a suction throttle valve, and an air release pipe that connects the discharge pipe between the compressor and the check valve and the inlet side of the air release valve. In the capacity control device of a lubricated rotary compressor,
A discharge solenoid valve branchedly connected to the discharge pipe and having an outlet side open to the atmosphere, and a timer means for opening the discharge solenoid valve for a predetermined time when switching to unload operation. A capacity control device for an oil-free rotary compressor featuring: