The function of the vacuum unit is to create the preliminary vacuum required for the Roots pump. Therefore, it is necessary to meet the allowable exhaust pressure of the water ring pump, which means that on one hand, we need to maximize the vacuum of the water ring pump, and on the other hand, we also need to find ways to increase the allowable exhaust pressure of the Roots pump.

In general, single-stage water ring vacuum pumps do not achieve high vacuum levels. Currently, the Roots pumps produced in our country require a higher preliminary vacuum. Therefore, it is not practical to use a single-stage water ring pump as the primary pump for Roots pumps. Instead, a two-stage water ring pump, which can enhance vacuum levels, is used as the primary pump. Utilizing a two-stage water ring pump can also improve the vacuum level of the unit.

The vacuum level of a single Roots pump is relatively low, especially when operated in combination with a water ring pump, which limits its application range. The overall vacuum level of the system may be low. However, by串联 two Roots pumps and then combining them with a water ring pump, the system's vacuum level can be improved.

Typically, in this type, two Roots pumps are connected in series, followed by a two-stage water ring pump as the primary pump to form the unit.

Even with a double-stage water ring pump, the increase in vacuum level is still within a certain range due to the limitation of the saturated steam pressure of water. The theoretical pressure of a water ring pump is the saturated steam pressure of water. Taking into account factors such as gas backflow, the actual pressure of a water ring pump is significantly higher than the saturated steam pressure at that water temperature. To improve the vacuum level of the primary pump, a combination of a water ring pump with an atmospheric pump can also be used.

Thus, the vacuum level after the atmospheric pump is connected can reach 20~30Torr, and if the water ring pump is combined with the second-stage atmospheric pump, the vacuum can reach 2~10Torr.

This unit is primarily used for vacuum systems that require the handling of large volumes of steam and high vacuum levels, such as in vacuum drying applications.

In vacuum systems that require handling large amounts of steam, water ring pumps are a suitable choice. However, due to their lower vacuum level, the overall vacuum level of the system is reduced. Although in vacuum extraction systems that demand higher vacuum levels, a high-vacuum mechanical vacuum pump is needed as a primary pump. Nevertheless, due to the high power consumption, low efficiency, and high noise of water ring pumps, using them as a pre-pump for a Roots pump in long-duration vacuum drying systems is not economically feasible.

In such cases, the gas-jet mechanical vacuum pump can be paralleled with the water-ring pump to serve as the primary pump for the Roots pump. During vacuum drying, first use the water-ring pump for pre-evacuation until a significant reduction in water vapor is achieved. Then, start the gas-jet mechanical vacuum pump and shut off the water-ring pump. In situations where a longer drying time is required, less cooling water and power are needed.