STEAM TRAPS

STEAM TRAPS

1Steam 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.Definition2If 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"Why its necessary to install Steam Traps3The 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 considerationMinimum steam lossLong life and dependable serviceCorrosion resistanceAir ventingCO2 venting at steam temperature

Function of Steam Traps4Mechanical traps operate by using the difference in density between steam and condensate. A float within the trap detects the variance in weight between a gas and a liquid.

Thermostatic traps detect the variation in temperature between steam and condensate at the same pressure. The sensing device operates the valve in response to changes in the condensate temperature and pressure.

Thermodynamic Traps use volumetric and pressure differences that occur when water changes state into gas. These changes act upon the valve directly.Types 5Ball float steam trapInverted bucket steam trapMechanical Steam Traps6Ball float steam trapCondensate reaching the trap will cause the ball float to rise, lifting the valve off its seat and releasing condensateThe valve is always flooded and neither steam nor air will pass through itAir vent allows the initial air to pass whilst the trap is also handling condensate.

7The mechanism consists of an inverted bucket which is attached by a lever to a valveThe Method of operation is shown in a figure in next slide(i) the bucket hangs down, pulling the valve off its seat(ii) the arrival of steam causes the bucket to become buoyant, it then rises and shuts the outlet.(iii) the trap remains shut until the steam in the bucket has condensed or bubbled through the vent hole to the top of the trap body8Inverted bucket steam trap

9Liquid expansion steam trapBalanced pressure steam trap10Thermostatic Steam TrapsAn oil filled element expands when heated to close the valve against the seatThe adjustment allows the temperature of the trap discharge to be altered between 60C and 100CThis makes it ideally suited as a device to get rid of large quantities of air and cold condensate at start-up11Liquid expansion steam trap

The operating element is a capsule containing a special liquid and water mixture with a boiling point below that of waterIn 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 ventingThe vapour pressure within the capsule causes it to expand and the valve shuts12Balanced Pressure Steam Trap

13Balance Pressure Steam Traps

Disc trap Impulse trapOrifice trap

14Thermodynamic Steam TrapsThe trap operates by means of the dynamic effect of flash steam as it passes through the trapOn start-up, incoming pressure raises the disc, and cool condensate plus air is immediately discharged from the inner ring, under the discHot 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 seatThe 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 rings15Disc Thermodynamic Steam Traps 16Disc Thermodynamic Steam Traps

The impulse trap (as shown in Figure) consists of a hollow piston (A) with a piston disc (B) working inside a tapered piston (C) which acts as a guide. At 'start-up' the main valve (D) rests on the seat (E) leaving a passage of flow through the clearance between piston and cylinder and hole (F) at the top of the piston. Increasing flow of air and condensate will act on the piston disc and lift the main valve off its seat to give increased flow. Some condensate will also flow through the gap between the piston and disc, through E and away to the trap outlet17Impulse steam trap

As the temperature of the condensate approaches its boiling point some of it flashes to steam as it passes through the gapAlthough 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 loadWhen the temperature of the condensate entering the trap drops slightly, condensate enters chamber B without flashing into steam18Impulse steam trapThese are devices containing a hole of predetermined diameter to allow a calculated amount of condensate to flow under specific pressure conditionsThey dont have any moving patsIn 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 trap19Orifice Steam Traps

20 Orifice Steam TrapsMechanicalcontinuous operationno action at no load, continuous at full loadgood energy conservationgood resistance to weargood corrosion resistanceexcellent ability to vent air at very low pressureexcellent operation against back pressurepoor resistance to damage from freezingfair ability to purge systemexcellent performance on very light loadspoor ability to handle dirtlarge comparative physical sizeclosed at mechanical failure

ComparisonThermostaticintermittent operationfair energy conservationfair resistance to weargood corrosion resistancegood abilities at low pressuresexcellent operation against back pressuregood resistance to damage from freezingexcellent ability to handle start-upfair ability to handle dirtsmall comparative sizeopen or closed at mechanical failure (depending on design)

Thermodynamicintermittent operationpoor energy conservationpoor resistance to wearexcellent corrosion resistancepoor abilities at low pressurespoor operation against back pressuregood resistance to damage from freezingexcellent ability to purge systempoor ability to handle dirtpoor ability to handle flash steamopen at mechanical failure

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