The compression ratio for each individual jet pump is limited. Depending upon the case in question, the desired vacuum may be very low so that several jet stages have to be connected in series. The motive steam pressure available and the desired vacuum are the decisive factor for the number of stages of these systems. The number of stages may be used to optimise the consumption of motive steam. Direct series connection of the jet pumps is possible, but not advisable from the point of view of power consumption, as the next stage in each case has to draw in and compress the motive steam from the previous stage. For this reason, condensers are connected between the individual stages. In a high vacuum, the condensation temperature of media to be drawn off is close to or below the cooling-water temperature. Here, the jet pumps must be aligned directly in series. It is also necessary to provide the first stage(s) of the vacuum system with a heating jacket to prevent the jet device from freezing up.
For the best possible matching to the case in question, a variety of designs are offered:
- condensation by means of surface condensers direct-contact condensers
- combination with a downstream water-ring vacuum pump as an atmospheric stage, designs in a wide variety of materials, etc.
Every system is tailor-made to customer requirements. The fields of application for multi-stage steam-jet vacuum systems are found in numerous branches of industry, eg:
- refrigeration plants
- crystallisation plants
- distillation plants
- deodorising plants
- polymerisation plants
- systems for the evacuation of turbine condensers