A syphon ejector is similar in construction to a standard steam jet ejector. However, the suction fluid is a liquid, usually water, instead of a gas.

Syphons are used primarily as sump pumps, with a maximum suction lift of 30-32 ft. of water when discharging to atmospheric pressure. The syphon may be lowered down into a pit to take a higher pressure differential as discharge head rather than suction lift. Syphons can also be used as effective heaters where a pressure increase across the unit is required.


In a Syphon, motive steam is used to increase the pressure of the water. Since motive steam condenses in the water, there is also a measurable temperature rise across the unit. Again, care must be taken to ensure that all the motive steam condenses in the water, and that the water doesn’t boil inside the syphon. Otherwise cavitation and line hammer are possible, and pumping will temporarily cease.


A syphon can use any condensable vapor to pump any liquid. Noncondensable (e.g. air) motivated units are generally not recommended due to problems with air hammer inside the syphon.