Steam trap is a type of automatic valve that filters out condensate (i.e. condensed steam) and non-condensable gases such as air without letting steam escape.
If condensate is not drained immediately or trapped from the system, it reduces operating efficiency by slowing the heat transfer process and can cause physical damage through the phenomenon known as “Water Hammer”
The job of the steam trap is to get condensate, air and Co2 out of the steam heated unit as fast as they accumulate. In addition, for overall efficiency and economy, the trap must also have following design and operating consideration
- Minimum steam loss
- Long life and dependable service
- Corrosion resistance
- Air venting
- CO2 venting at steam temperature
Mechanical Traps :-
Thermostatic Steam Trap :–
Liquid Expansion Steam Trap
An oil filled element expands when heated to close the valve against the seat.The adjustment allows the temperature of the trap discharge to be altered between 60°C and 100°C. This makes it ideally suited as a device to get rid of large quantities of air and cold condensate at start-up.
Balanced Pressure steam Trap :
The operating element is a capsule containing a special liquid and water mixture with a boiling point below that of water.In the cold conditions that exist at start-up, the capsule is relaxed. The valve is off its seat and is wide open, allowing unrestricted removal of air. This is a feature of all balanced pressure traps and explains why they are well suited to air venting.The vapour pressure within the capsule causes it to expand and the valve shuts.
Thermodynamic Steam Trap :-
Disc Thermodynamic Steam Trap :
The trap operates by means of the dynamic effect of flash steam as it passes through the trap.On start-up, incoming pressure raises the disc, and cool condensate plus air is immediately discharged from the inner ring, under the disc. Hot condensate flowing through the inlet passage into the chamber under the disc drops in pressure and releases flash steam moving at high velocity. This high velocity creates a low pressure area under the disc, drawing it towards its seat.The flash steam pressure builds up inside the chamber above the disc, forcing it down against the incoming condensate until it seats on the inner and outer rings.
Impulse Steam Trap :
As the temperature of the condensate approaches its boiling point some of it flashes to steam as it passes through the gap.Although this is bled away through hole F it does create an intermediate pressure over the piston, which effectively positions the main valve to meet the load.When the temperature of the condensate entering the trap drops slightly, condensate enters chamber B without flashing into steam.
Orifice Steam Trap :
These are devices containing a hole of predetermined diameter to allow a calculated amount of condensate to flow under specific pressure conditions.They don’t have any moving pats.In case of a small orifice, the condensate flows with much lower velocity through the opening, the much denser condensate will stop the steam. The consequence of this is, no fresh steam will leak through the trap.