Lever steam traps are in the thermodynamic trap category that are actuated by the principles of thermodynamics and fluid dynamics.
Thermodynamic steam traps are phase detectors in that they can discriminate between liquids and gases, but they do not discriminate between steam and air or other non-condensable gases. Therefore, they have a reduced ability to bleed-off those gases. Small amounts of steam may also be passed.
Lever steam traps are a variation of the thermodynamic piston trap. They operate on the same principle as piston steam traps, but with a lever action rather than a reciprocating piston action.
When the lever is closed, there is a limited flow through the annulus between the inlet valve and its seat (first orifice) which then enters the control chamber and flows out through the second or control orifice. Incoming condensate pushes the lever upward with a tilting motion and full flow goes under it and out the discharge port. Condensate flowing past the inlet seat (a restriction) experiences a pressure drop (in accordance with the laws of fluid dynamics) and it will flash into steam (in accordance with the laws of thermodynamics) when the condensate temperature is very close to steam temperature (saturation temperature). The localized lower pressure under the lever (created by the high velocity flow of flash steam) causes the lever and inlet valve to snap shut. This prevents steam flow through the trap.
When condensate with its cooler temperature again reaches the trap, it will reopen, repeating the cycle.
The control orifice has a continuous discharge which is helpful in passing air and other non-condensable gases during start-up. Steam loss through the control orifice is minimal.
Lever steam traps are designed for applications having especially large condensate loads and that benefit from the very rapid discharge of condensate after its formation.
Prior to selecting a steam trap for your application, review steam traps selection with its advantages versus disadvantages and additional steam trap types: Disc Steam Traps, Piston Steam Traps, Closed Float Steam Traps, Inverted Bucket Steam Traps, Open Bucket Steam Traps, Bimetallic Steam Traps, Bellows Steam Traps, Liquid or Solid Expansion Steam Traps (Wax Capsule Steam Trap), and Orifice Steam Traps.