(1) No-load start mode
This is a device that prevents the Air Compressor from starting to work before the drive motor reaches its full speed. The purpose of the control is to make the load on the motor as small as possible when it starts to work. There are mainly the following ways to reduce the load on the motor.
①Suction unloading valve
Most Air Compressors are equipped with a suction unloading valve, which is used to remove the load on the compressor. Since the suction unloading valve is open when the compressor is operated by the shoulder, the air sucked into the pump cylinder during the suction stroke will start from the open state. The air is discharged to the valve during the suction unloading period, so the air will not accumulate in the cylinder, thereby reducing the load on the motor.
② Diaphragm (or piston) unloader
It is a mechanism for opening and closing the suction unloading valve, mainly including a diaphragm (or piston) and a connecting rod (or pin). The air to drive the diaphragm or piston is controlled by a pilot valve (3-way valve). The pilot valve is controlled by the operating speed, oil pressure and air pressure of the compressor.
③ Pilot valve (three-way valve) unloader
It has two forms, one is used on compressors that use splash lubrication, its valve is located in the center of the crankcase, opposite to the pulley, when the compressor is running, the valve is open to unload, A centrifugal pressing mechanism is installed inside the crankshaft in the crankcase, which can control the opening and closing of the valve. The second type of pilot valve unloader is used on compressors that use pressure lubrication. It is located slightly off the center of the crankcase, opposite to the pulley, and the oil pressure can be directly applied to this pilot valve to control the opening and closing of the valve. When the oil pressure is sufficient, the pilot valve is closed and the compressor operates normally. When the oil pressure drops or the compressor speed drops to 4oOr/min, the pilot valve opens to unload the compressor.
(2) Constant speed unloader
The role of the constant speed unloader is to ensure that the motor and compressor run continuously and keep the outlet pressure of the compressor consistent with the set value. This unit is suitable for use where there is an uninterrupted demand for compressed air.
A constant speed unloader is usually used in conjunction with a suction unloader valve and a diaphragm unloader to control the normal pressure of the compressor. When the compressor continues to run and the air storage tank reaches its required working pressure, the constant speed unloader is in the open state, and the air is sent to the diaphragm unloader to unload the compressor. At this time, the compressor is still running, but In fact, it is not supercharged and is in an idling state. Only when the pressure storage air in the air storage container is consumed and the pressure drop exceeds the set pressure upper limit of 69kPa, the constant speed unloader will close, stop supplying air to the diaphragm and release the air applied to the diaphragm to make the compression The machine starts producing gas again.
(3) Unloading method of dual control
This control method is actually obtained by combining a constant speed unloader and a pressure switch, so that the motor and compressor can operate continuously or intermittently, and is suitable for use in occasions where the requirements for the compressor are often changed.
The whole system includes the components required for no-load start, constant speed unloader, shut-off valve and pneumatic check valve. The structure of dual control is shown in Figure 3-38.
The stop valve is installed at the air inlet of the constant speed unloader. The starting pressure of the constant speed unloader is at least 68.9kPa lower than the upper limit of the set gas production pressure. When the shut-off valve is closed, the compressor is controlled by the pressure switch for intermittent operation, and when the shut-off valve is opened, the compressor is controlled by the constant-speed unloader for continuous operation. This control method provides great convenience to the user. When a large amount of compressed air is needed, the compressor can be operated continuously, and when the air consumption is small or only a certain pressure is maintained for small-scale work, it can be switched to intermittent operation.
Other control mechanisms also include manual unloader and gasoline engine idling device. The manual unloader is a device that can manually open the suction unloading valve to unload the compressor. It is composed of a suction unloading valve and a screw or lever connecting rod for opening and closing the valve. Gasoline engine idling device is an air control device installed on the compressor driven by gasoline engine. When the air pressure of the compressor reaches the set pressure, the idling device will make the gasoline engine enter the idling state to reduce its power consumption.
