In general, using a water ring pump as the front stage pump is more advantageous than other vacuum pumps for Roots vacuum units. This is mainly because it can extract a large amount of condensable steam, especially when the mechanical vacuum pump with gas ballast oil seal has insufficient ability to remove condensable steam, or the solvent used can deteriorate the pump oil and affect its performance, or when the vacuum system does not allow oil pollution. When choosing a vacuum unit, it is generally necessary for the ultimate vacuum degree of the vacuum unit to be at least half to one order of magnitude higher than the working vacuum degree in order to meet the usage requirements.

There are roughly several types of Roots water ring vacuum units:

• Roots pump+water ring pump: The function of the water ring pump in the unit is to create the necessary reserve vacuum for the Roots pump. Generally, the ultimate vacuum degree of a single-stage water ring pump is not high, and currently, the Roots pump produced in China requires a high pre vacuum. Therefore, in practice, a single-stage water ring pump is not used as the front stage pump of the Roots pump, but a two-stage water ring pump that can improve the ultimate vacuum degree is used as the front stage pump. Using a two-stage water ring pump can also improve the ultimate vacuum degree of the unit.
• Roots pump+Roots pump+water ring pump: The ultimate vacuum degree of a Roots pump is relatively low, especially when it is combined with a water ring pump, the range of use is limited, and the ultimate vacuum degree of the entire unit may be lower. However, if two Roots pumps are connected in series and combined with a water ring pump, the ultimate vacuum degree of the unit can be greatly improved.
• Roots pump+Roots pump+Roots pump+water ring pump: If two Roots pumps+water ring pump cannot meet the vacuum requirements, an additional Roots pump can be added. This type of Roots water ring vacuum unit has been widely used in high vacuum processes such as vacuum freeze-drying.
  
  
  Model representation method
  For example: JZJ2S1200---4.2.1
  J is the first letter of the unit. The ZJ main pump is a Roots vacuum pump. 2S is a primary pump and a two-stage water ring pump. 1200 is the main pump (Roots pump) with a pumping speed of L/s. 4.2.1 is the code for pumping speed ratio.
  

  JZJ2S series Roots water ring vacuum unit technical specifications:

  　

  Model	Main pump	Backing Pump	pumping speed (L/S)	Ultimate pressure (Pa)	total power (Kw)
  JZJ2S30-1	ZJ30	2SK-1.5	30	2.67×102	4.75
  JZJ2S70-2	ZJ70	2SK-1.5	70	2.67×102	5.5
  JZJ2S70-1	ZJ70	2SK-3	70	2.67×102	9
  JZJ2S150-2	ZJ150	2SK-3	150	2.67×102	10.5
  JZJ2S150-1	ZJ150	2SK-6	150	2.67×102	18
  JZJ2S300-2	ZJ300	2SK-6	300	2.67×102	19
  JZJ2S300-1	ZJ300	2SK-12	300	2.67×102	26
  JZJ2S600-2A	ZJ600	2SK-12	600	2.67×102	27.5
  JZJ2S600-2B	ZJ600	2SK-20	600	2.67×102	42.5
  JZJ2S70-2.1	ZJ70	ZJ30、2SK-1.5	70	6.7×10	6.25
  JZJ2S150-2.1	ZJ150	ZJ70、2SK-3	150	6.7×10	12
  JZJ2S300-2.1	ZJ300	ZJ150、2SK-6	300	6.7×10	22
  JZJ2S600-2.1	ZJ600	ZJ300、2SK-12	600	6.7×10	31.5
  JZJ2S150-4.1	ZJ150	ZJ30、2SK-1.5	150	6.7×10	7.75
  JZJ2S300-4.2	ZJ300	ZJ70、2SK-1.5	300	6.7×10	9.5
  JZJ2S300-4.1	ZJ300	ZJB70、2SK-3	300	6.7×10	13
  JZJ2S600-4.2	ZJ600	ZJB150、2SK-3	600	6.7×10	16
  JZJ2S600-4.1	ZJ600	ZJB150、2SK-6	600	6.7×10	23.5
  JZJ2S1200-4.2	ZJ1200	ZJB300、2SK-6	1200	6.7×10	30
  JZJ2S1200-4.1	ZJ1200	ZJB300、2SK-12	1200	6.7×10	37
  JZJ2S2500-4.2A	ZJ2500	ZJB600、2SK-12	1200	6.7×10	44.5
  JZJ2S2500-4.1B	ZJ2500	ZJB300、2SK-20	1200	6.7×10	59.5
  JZJ2S300-4.2.1	ZJ300	ZJ70、ZJB30、2SK-1.5	300	5×10-1	10.25
  JZJ2S600-4.2.1	ZJ600	ZJ150、ZJB70、2SK-3	600	5×10-1	17.5
  JZJ2S1200-4.2.1	ZJ1200	ZJ300、ZJB150、2SK-6	1200	5×10-1	33
  JZJ2S2500-4.2.1	ZJ2500	ZJ600、ZJB300、2SK-12	2500	5×10-1	48.5

  Explanation: 1. The above are industry recommended standard models, and customized designs can also be made according to specific user requirements 2. The technical specifications of a single pump can be found in the instructions of each pump 3. The front-end pump with the above specifications can be replaced by a 2YK series oil ring pump, which reduces the ultimate pressure accordingly.