The power required by the roots vacuum pump to compress the gas is proportional to its pressure difference. Once the gas pressure difference is too high, roots pump may be overloaded, which make the motor windings burned. The main methods to solve this problem are as below:
1. Using Mechanical Automatic Pressure Regulator Bypass Valve
The bypass valve is installed in the bypass line between the outlet and the inlet of the roots pump. This valve controls the pressure difference between the inlet and outlet of the pump and make sure that the pressure difference not exceed the rated value. If the differential pressure reaches the rated value, the valve opens automatically by the pressure difference action to make outlet connects inlet, and the differential pressure between inlet and outlet drops rapidly. At this time, the roots pump works under almost no differential pressure. If the pressure difference is lower than the rated value, the valve will automatically close and the gas will be pumped by the backing pump through the roots pump. Besides, the roots pump with a bypass relief valve can be started simultaneously with the backing pump, which makes the unit easy to operate.
2. Using Hydraulic Coupling
Using hydraulic couplings can also prevent overloads of the pump and allow the pump to operate at high pressure differentials. The hydraulic coupling is installed between the pump and the motor. In normal operating conditions, the hydraulic coupling transmits the nominal torque from the motor end to the pump. The maximum differential pressure of the roots pump is determined by the maximum torque transmitted by the hydraulic coupling, and the maximum torque that can be transmitted by the hydraulic coupling is regulated by the amount of fluid therein. When the pump works under the high pressure difference or starts simultaneously with the backing pump, a rotational speed difference or a slip occurs inside the liquid coupling, and only a certain torque is transmitted to decelerate the pump. With the pumping proceeding, the gas load decreases, and the roots pump gradually accelerates to the rated speed.
3. Using Vacuum Electrical Components to Control the Pump Inlet Pressure
Pressure sensitive elements such as a vacuum bellows relay or an electrical contact vacuum pressure gauge are placed at the entrance of the roots pump. After the vacuum system starting, the pressure sensitive element sends out a signal and the roots pump is started via the electric control system (if the bypass line of roots pump is installed in the vacuum system, close the bypass line) when the pressure at the inlet is lower than the set value (permissible starting pressure of the pump). If the inlet pressure is higher than the set value, the roots pump is automatically turned off (or the bypass line valve is opened at the same time) to ensure the reliable operation of the roots pump.