Differential pressure of roots vacuum pump and relief valve

What is the maximum allowable differential pressure and relief valve differential pressure for roots vacuum pumps
Roots vacuum pump is a rotary positive displacement pump. According to the different working pressure range, it is divided into low vacuum (direct exhaust atmosphere) roots pump and middle vacuum roots pump. According to the different cooling medium, the vertical exhaust air roots pump can be divided into air-cooled roots pump and (water-cooled) wet roots pump. Middle vacuum roots pump can not withstand high pressure difference, so must be equipped with the front pump to work. What is the maximum allowable differential pressure and relief valve differential pressure for roots vacuum pumps? This paper discusses the maximum allowable pressure difference and relief valve pressure difference of middle vacuum roots pump (hereinafter referred to as roots pump).
The maximum allowable pressure difference is one of the most important performance indexes of roots pump. It refers to the maximum value of the difference between outlet pressure and inlet pressure allowed without failure when the inlet pressure of roots pump is equal to or less than 1 kPa for continuous operation for 1 h. Maximum allowable pressure difference is in the maximum power consumption of the measure of roots pump and one of the important indices for trouble-free operation under high temperature, which is under the maximum power consumption test of roots pump shaft, rotor, bearing and gear strength, and the rotor, the reliability of the connection between gear and shaft, under the high temperature test whether all the parts of the roots pump clearance can guarantee the normal operation.
Roots pumps with an overflow valve can be started at the same time as the front pump and can work continuously at any inlet pressure. The overflow valve of roots pump will automatically open when the pressure difference exceeds a specified value, connecting the inlet and outlet, which can effectively prevent the overload of the pump without affecting the normal operation of the pump. Therefore, the pressure difference of the overflow valve is defined as the difference of the pressure on the upper and lower sides of the valve when the overflow valve of roots pump is opened, and the operation under this pressure difference is trouble-free for 1 h. It is important to point out that in the past there has been a misconception that the purpose of the overflow valve was simply to prevent overloading of the pump and to increase the additional power consumption. In fact, this view is one-sided, the biggest advantage of roots pump with overflow valve is to expand the operating range of the pump, it covers a wide pressure range from atmospheric pressure to 1022Pa, and can effectively reduce the vacuum system in the low vacuum pumping time (30% ~ 50%).
The maximum allowable differential pressure is only a measure and assessment of roots vacuum pump manufacturing and operation quality of an index, does not mean roots pump can be in this differential pressure for a long time to run, does not mean that must be in this differential pressure to start. And roots pump with overflow valve can be determined according to the requirements of its vacuum process flow. Roots pump with no overflow valve is suitable for medium vacuum operation due to the large maximum allowable pressure difference and can withstand a larger pressure difference in short time operation. In the thick and low vacuum, the former pump can be used to pump air through the bypass (pre-pumping) pipeline.

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