JPH0792069B2 - Screw compressor - Google Patents

Description

TECHNICAL FIELD The present invention relates to an oil-free screw compressor.

(Prior Art) Conventionally, an oil-free type screw compressor shown in FIG. 2 has been known (JP-A-60-166785).

This screw compressor includes a passage 5 that passes through a primary cooler 2, a check valve 3, and a secondary cooler 4 in order from a screw compressor body 1 using a screw rotor, and a secondary cooler 4 of this passage 5.
It has a flow path 8a that branches from the outlet side of the above to reach the rotor chamber in the screw compressor body 1 via the solenoid valve 6.
Then, after the discharge gas from the screw compressor body 1 is cooled by the primary cooler 2 and the secondary cooler 4, a part of the cooling gas is returned to the rotor chamber by opening the solenoid valve 6 to compress the compressed gas. It is designed to be cooled.

On the other hand, a screw compressor shown in FIG. 3 which is configured to be switchable between full load operation and unload operation is known (Japanese Patent Laid-Open No. 59-93985), and parts common to those in FIG. 2 are the same. Numbered.

This screw compressor goes through ports a and b of intake air control valve 9, and then screw compressor main body 1, primary cooler 2, check valve in order.
A flow path 11 that extends from the third and second coolers 4 to the receiver tank 10 and extends from there to the point where compressed gas is used;
Branch from the portion between the next cooler 2 and the check valve 3 to
It has a flow path 12 reaching the c and d ports of the intake control valve 9 that is not in communication with the a and b ports, and also has a check valve 3 and a secondary cooler 4.
Between this and the pressure switch 13
If the pressure in this part is less than the set value by this pressure switch 13, the ports a and b are opened, and the ports c and d are closed, while if the set value is exceeded, the ports a and b are opened. Are closed or throttled, and the c and d ports are opened.

And because the amount of compressed gas used is large, the receiver tank 10
When the internal pressure reaches a set value, for example, 7 kg / cm ² G or less, the a, b ports are opened and the c, d ports are closed, and all the discharge gas from the screw compressor body 1 reaches the receiver tank 10. On the other hand, when the amount of compressed gas used decreases and the pressure inside the receiver tank 10 exceeds 7 kg / cm ² G, the ports a and b are closed or throttled, while the ports c and d are opened. , The discharge gas from the screw compressor body 1 is released to the outside of the machine through the c and d ports by the flow path 12, and the check valve 3
This prevents the gas in the receiver tank 10 from flowing into the flow path 12.

Therefore, from FIG. 2 and FIG.
As a screw compressor capable of switching between full load operation and unload operation, one having a structure in which FIGS. 2 and 3 are combined is conceivable. That is, as shown in FIG. 4 by assigning the same reference numerals to the portions common to FIG. 2 and FIG.
A passage 11 that passes through the b port, the screw compressor main body 1, the primary cooler 2, the check valve 3, the secondary cooler 4, the receiver tank 10,
A flow path 12 that branches from a portion between the primary cooler 2 and the check valve 3 of the flow path 11 and reaches the c and d ports of the intake control valve 9, the secondary cooler 4 of the flow path 11, and the receiver. It is conceivable to have a flow path 8b that branches from the portion between the tank 10 and the tank 10 and reaches the rotor chamber of the screw compressor body 1 via the electromagnetic valve 6. Then, in this case, the flow path 12 is used for releasing the compressed gas during the unloading operation, and the flow path 8b is used for cooling the compressed gas in the same manner as above.

(Problems to be Solved by the Invention) In the screw compressor shown in FIG. 4, which is an oil-free type which can be considered by simply combining the above-mentioned conventional devices and which can be switched to full load operation or unload operation, In order to prevent the compressed gas in the receiver tank 10 from flowing out of the intake control valve 9 through the flow passage 8b and the flow passage 12 to the outside of the machine when the operation is started, the pressure in the flow passage 8b is always required. The solenoid valve 6a interlocking with the switch 13 is required, and the device becomes complicated accordingly. Moreover, the more complex the device, the greater the chance of failure. For example, in a single-stage compressor having a discharge pressure of 6 to 7 kg / cm ² atmosphere, the operation of turning on / off the solenoid valve 6a is actually performed at intervals of about 30 seconds. When the solenoid valve 6a is frequently turned on and off in this way, the solenoid valve 6a cannot sufficiently follow the on / off control signal, so that the flow passage 8b, the compressor body 1, There is a waste of releasing the once compressed high pressure gas to the outside via the flow path 12. Further, frequent on / off at short time intervals easily causes the solenoid valve 6a to malfunction, and if the solenoid valve 6a fails, a fatal accident for the compressor will occur.

Further, since compressed drain water is contained in the compressed gas having a low temperature that has exited the secondary cooler 4, the drain water will be returned to the rotor chamber, and therefore the screw in the screw compressor body 1 will be returned. There is a problem such as rust on the rotor and casing.

The present invention has been made in view of the above conventional problems,
An object of the present invention is to provide a screw compressor capable of simplifying the apparatus and suppressing the temperature rise in the rotor chamber without generating drain water from the gas returned to the rotor chamber.

(Means for Solving the Problems) In order to solve the above problems, the present invention provides a
After passing through port b, the first flow path that passes through the primary cooler, check valve, and secondary cooler in order from the oil-free screw compressor body, and the primary cooler and check valve of this flow path Has a second flow path that branches from a portion between the above-mentioned intake valves and does not communicate with the above-mentioned a and b ports and reaches the c and d ports of the above-mentioned intake control valve. A pressure switch is provided to detect pressure, and this pressure switch opens ports a and b when the pressure in this part is below the set value.
While c and d ports are closed, if the set values are exceeded, a and b
In a screw compressor formed so that the ports are closed or throttled and the c and d ports are opened, the screw compressor is branched from a portion of the first flow path between the primary cooler and the check valve. It was formed by providing a third flow path to the rotor chamber in the main body.

(Operation) With the above-described configuration, the check valve does not cause the reverse flow of gas from the downstream side portion of the secondary cooler during the unloading operation by the check valve without providing the solenoid valve in the third flow path. During full load operation and unload operation, drain water is not entrained from the cooling gas returned to the rotor chamber,
The temperature rise in the rotor chamber is suppressed, expansion of the screw rotor and casing, rusting in the screw compressor body,
The problem caused by this is also eliminated.

(Example) Next, one example of the present invention will be described with reference to the drawings.

FIG. 1 shows a screw compressor according to the present invention, which is substantially the same as the screw compressor shown in FIG. 4 except for a flow path for cooling a compressor gas, and parts corresponding to each other. Are denoted by the same reference numerals and description thereof will be omitted.

As shown in the figure, the present screw compressor is provided with a flow passage 8 that branches from a portion of the flow passage 11 between the primary cooler 2 and the check valve 3 to reach the rotor chamber in the screw compressor main body 1. , 4th
Even if the solenoid valve 6a shown in the figure is not provided, backflow from the receiver tank 10 to the rotor chamber does not occur. That is,
Even if the unloading operation is performed by opening the c and d ports of the intake air control valve 9, the check valve 3 prevents the reverse flow of gas from the receiver tank 10.

In addition, by returning the gas having a relatively high temperature, which has just been cooled by the primary cooler 2 to the rotor chamber before entering the secondary cooler 4, inflow of drain water into the screw compressor main body, And prevent the generation of rust due to drain water,
The temperature rise in the rotor chamber is suppressed.

(Effects of the Invention) As is apparent from the above description, according to the present invention, the primary cooler and the check valve are sequentially passed from the oil-free screw compressor main body after passing through ports a and b of the intake air control valve. The first flow path passing through the valve and the secondary cooler, and the part of the flow path between the primary cooler and the check valve that branches off and does not communicate with the a and b ports. , and a second flow path to the d port, and a pressure switch is provided on the outlet side of the check valve so as to detect the pressure in this portion, and this pressure switch makes the pressure in this portion less than or equal to the set value. In the case of, the a and b ports are opened and the c and d ports are closed, while when the set value is exceeded, the a and b ports are closed or throttled and the c and d ports are opened. In the screw compressor, the first
Branch from the part between the primary cooler and the check valve in the flow path,
A third flow path leading to the rotor chamber in the screw compressor body is provided and formed.

Therefore, a solenoid valve is provided in this passage by simply providing a third passage that simply connects the portion between the primary cooler of the first passage and the check valve with the rotor chamber. There is no backflow of the compressed gas from the outlet side of the secondary cooler even without the unloading operation, and therefore not only the solenoid valve, but also the control circuit for interlocking the pressure switch and the solenoid valve becomes unnecessary. As a result, as in the case of the compressor shown in FIG. 4, there is a concern that a compressed gas on the downstream side of the check valve may leak outside the machine due to a delay in the response of the solenoid valve and a serious accident may occur due to a failure of the solenoid valve. Also disappears.

Further, since the third flow path is made simple as described above, it is possible to automatically adjust the amount of the cooling gas to be returned to the compressor body without using any control device. That is, when the discharge pressure is high, a large amount of heat is generated in the rotor chamber.
When the discharge pressure is low, the amount of heat generated in the rotor chamber is small, and the amount of gas flowing through the third flow path is small.

In addition, since the relatively high temperature gas containing no drain water is returned to the rotor chamber, the drain water does not flow into the screw compressor main body and the rotor and the casing are not corroded. Can suppress the temperature rise. As a result, the discharge temperature rises, the screw rotors due to thermal expansion, and the gap between them and the casing are reduced, and further damage to the screw rotors or the contact between them and the casing causes an oil-free system. It is possible to prevent the fatal problem of the screw compressor from occurring.

[Brief description of drawings]

FIG. 1 is an overall configuration diagram of a screw compressor according to the present invention, FIGS. 2 and 3 are overall configuration diagrams of a conventional screw compressor, and FIG. 4 is a combination of devices shown in FIGS. 2 and 3. It is a whole block diagram of the screw compressor concerning. 1 ... Screw compressor body, 2 ... Primary cooler, 3 ...
Check valve, 4 ... Secondary cooler, 8,11 ... Flow path, 13 ... Pressure switch.

Claims (1)

[Claims] 1. A first flow path (11) passing through the a and b ports of the intake control valve, and then the oil-free type screw compressor main body in order through the primary cooler, the check valve and the secondary cooler. And the intake control valve c, d branching from the portion of the flow path between the primary cooler and the check valve and not communicating with the a and b ports.
It has a second flow path (12) to reach the port, and a pressure switch is provided on the outlet side of the check valve to detect the pressure of this part. With this pressure switch, the pressure of this part is set to a set value. In the following cases, ports a and b are opened and ports c and d are closed, while when the set values are exceeded, ports a and b are closed or throttled and ports c and d are opened. In the screw compressor, the third flow path (8) that branches from the portion of the first flow path (11) between the primary cooler and the check valve to reach the rotor chamber in the screw compressor body. A screw compressor characterized by being provided with.