©2008 Armstrong International, Inc. Basic Steam Trap Operation

©2008 Armstrong International, Inc.

Basic Steam Trap Basic Steam Trap OperationOperation

What MUST a Steam Trap do?What MUST a Steam Trap do?What MUST a Steam Trap do?What MUST a Steam Trap do?

A Steam Trap must remove condensate, air, and CO2 out of

the system as quickly as it collects.

2“Expect many enjoyable experiences!”

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®Intelligent System Solutions S T E A M • A I R • H O T W A T E R


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Minimize steam loseMinimize steam lose

Corrosion resistanceCorrosion resistance

CO2 VentingCO2 Venting

Freedom from dirt problemsFreedom from dirt problems

Long life and dependable service

Long life and dependable service

Air VentingAir Venting

Operation against backpressure

Operation against backpressure

A Steam Trap Must Also:A Steam Trap Must Also:A Steam Trap Must Also:A Steam Trap Must Also:


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What makes up a Steam TrapWhat makes up a Steam TrapWhat makes up a Steam TrapWhat makes up a Steam Trap

• A Steam Trap has an orifice

• An orifice alone is not a steam trap

– If flow changes, orifice is not correct

– If pressure drop changes, orifice is not correct

– The orifice must change size as conditions change

Orifice

Inlet Connection

Outlet Connection

Body


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• A Steam Trap should have a valve

– A valve may be fully opened and fully closed or modulated to vary the size of the orifice as conditions change

Orifice

Inlet Connection

Outlet Connection

Body

Valve


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• A Steam Trap should have an Operator

– An operator senses when to move the valve and supplies the power to move the valve

– Traps are different in the types of valve and the types of operator they use

Inlet Connection

Outlet Connection

Body

Valve

Orifice

Operator

Trap/Operator Types

Mechanical

Use difference in density

between steam and condensate

to operate valve. A float operates the

valve.

Thermodynamic

Steam (flash) –flow operates

valve

Thermostatic

Sense temperature change of

condensate to operate valve


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Thermostatic Trap TypesThermostatic Trap TypesThermostatic Trap TypesThermostatic Trap Types

• Bellows balanced pressure – High capacity

• Wafer/Diaphragm balanced pressure– Low capacity

• Bi-metallic– High and low capacity


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Bellows Balanced PressureBellows Balanced PressureBellows Balanced PressureBellows Balanced Pressure

SteamSteamCondensate

Liquid fill

Bellows

Valve

Seat


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Bellows Balance PressureBellows Balance PressureBellows Balance PressureBellows Balance Pressure

Bellows Balance Pressure

Modulation Poor

Backpressure Good

Dirt Fair

Wear Fair

Water Hammer Poor

Freezing Good


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Simple Bi-Metal ElementSimple Bi-Metal ElementSimple Bi-Metal ElementSimple Bi-Metal Element

High expansion metal

Low expansion metal

Cold

Hot


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Simple Bi-Metal OperationSimple Bi-Metal OperationSimple Bi-Metal OperationSimple Bi-Metal Operation

Valve inside trap

• Pressure holds valve closed; valve toggles

• Back pressure can blow trap open

• Opening and closing temperatures wide apart

• Must sub-cool deeply to prevent steam loss


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Bi-Metal DisksBi-Metal DisksBi-Metal DisksBi-Metal Disks

Valve in outlet

• Pressure opposes closing.

• Does not toggle.

• Some thermodynamic action; roughly follows steam saturation curve.

• Acts as check valve when pressure is lost.

• Good for use in super-heated applications.

A. Trap body

B. Disk bonnet

C. Disk

D. Inner seat ring

E. Outer seat ring

F. Inlet port

G. Outlet port and groove

Disk Trap Orifices in SeriesDisk Trap Orifices in SeriesDisk Trap Orifices in SeriesDisk Trap Orifices in Series

P2

ABC

DE

F G

H

DE

F G

H

E D

P1 P3


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Disk Trap Start-upDisk Trap Start-upDisk Trap Start-upDisk Trap Start-up

• Condensate pressure pushes disk off seat

• Full capacity flow

• Two pressure drops


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Disk Trap Flashing SteamDisk Trap Flashing SteamDisk Trap Flashing SteamDisk Trap Flashing Steam

• Condensate near steam temperature flashes to steam in inlet port

• Pressure drops with flow through restriction under disk

• Pressure difference (P2 - (<<P2)) slams disk onto seats

P1

P2

<<P2

P3


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Disk Trap ClosedDisk Trap ClosedDisk Trap ClosedDisk Trap Closed

• P2 – P3 x disk area > P1 x inlet port area + P3 x outlet port area

• Closing force greater than opening forces so disk stays on seat

• Condensing flash steam above disk relieves pressure until opening forces are greater; disk snaps open

• A bleed groove is used to help with control of the pressure in the control chamber.


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Disk and Seat WearDisk and Seat WearDisk and Seat WearDisk and Seat Wear

• Disk slammed hard onto seats and rolls as it seats

– Edge of disk wears rapidly

– Edge of outer seat ring wears rapidly

• High velocity flow of condensate flash steam and dirt between disk and inner seat ring

– Inner seat ring wears rapidly

– Disk surface erodes rapidly

Uneven contact of disk on seat causes wear

Disk Wear Seat Wear

Flat valve and seats

require near perfect

flatness to seal

Two seats to seal


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Thermodynamic TrapsThermodynamic TrapsThermodynamic TrapsThermodynamic Traps


Thermodynamic Traps

Modulation Poor Fair

Backpressure Good Poor

Dirt Fair Poor

Wear Fair Poor

Water Hammer Poor Good

Freezing Good Good


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Mechanical TypesMechanical TypesMechanical TypesMechanical Types

Float & Thermostatic Inverted Bucket

LinkageFixed Pivot

Air Vent Valve

Valve Ball

Seat


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Simple Float TrapSimple Float TrapSimple Float TrapSimple Float Trap

Fixed Pivot

Air Vent Valve

Valve Ball

Seat

Linkage


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Float and ThermostaticFloat and ThermostaticFloat and ThermostaticFloat and Thermostatic

Condensate enters

Ball rises opening valve to full capacity

Bellows cold; vent open to air and/or condensate flow

Condensate flow decreases

Ball moves downward; valve open less

Valve modulates to balance outlet flow = inlet flow

Steam enters; steam air mixture closes vent; temperature below saturation

Start-Up Modulating Air Venting

Air increases; temperature drops; vent opens

Steam lost with air removal

Dirt falls to bottom; may stop ball from dropping holding valve open; may plug valve


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F&T TrapsF&T TrapsF&T TrapsF&T Traps


Thermodynamic Traps

F&T Traps

Modulation Poor Fair Good

Backpressure Good Poor Good

Dirt Fair Poor Poor

Wear Fair Poor Good

Water Hammer Poor Good Poor

Freezing Good Good Poor


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Inverted BucketInverted BucketInverted BucketInverted Bucket

A. BucketB. Valve on linkage

• Sized for maximum flow at maximum pressure difference

C. Air VentD. Body

• Material based on pressure and cost

E. Inlet

D

CB

A

EBottom inlet – Top outletOther configurations available


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IB At Start-UpIB At Start-UpIB At Start-UpIB At Start-Up

Low velocity

flow

• Condensate fills body

• Condensate surrounds all internals; pressure same on all surfaces of all internals; no water hammer damage

• Valve wide open for maximum flow rate; quick drain

• Air pushed out ahead of condensate through wide open valve; quick vent

• Small dirt particles suspended in flow and flushed through valve

• Large dirt particles are too heavy to be carried to valve by low velocity flow around bucket lip, so they stay at bottom

• No strainer needed in most applications

Condensate

Valve wide open


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IB ClosedIB ClosedIB ClosedIB Closed

• Start-up condensate accumulation gone

• Steam enters depressing water level in bucket

• When bucket approximately 2/3 full of steam, bucket becomes buoyant

• Bucket floats valve to seat

• Pressure difference pushes valve softly into seat

• Valve seats tightly

• Air passes through vent to collect at top of trap Condensate

level

Valve tightly closed


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IB FillingIB FillingIB FillingIB Filling

• Valve closed; condensate continues to enter trap; no condensate back-up

• Intermittent discharge but continuous drain

• Water condenses and displaces steam; water level rises

• Air continually rises through vent to top of trap

• If air accumulation becomes excessive, air will depress water level and open valve

Condensate

Valve tightly closed

Steam


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IB OpeningIB OpeningIB OpeningIB Opening

Small dirt flushed

Valve wide open• Water level continues to rise

• Bucket 2/3 full of water loses buoyancy; bucket falls pulling valve wide open

• Air flushed out

• Full capacity flow carries small dirt particles to wide open valve to flush each cycle

• Pressure changes affect capacity only

• Steam in trap continuously; condensate and air discharged at steam temperature

• Cycle rate adjusts immediately with flow changes


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IB Thermic VentIB Thermic VentIB Thermic VentIB Thermic Vent

Bi-metal thermic vent• Open at start-up for

quick vent of air under bucket

• Closed at steam temperature; normal vent enough for operating air venting load


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Inverted BucketInverted BucketInverted BucketInverted Bucket


Thermodynamic Traps

F&T Traps Inverted Bucket

Modulation Poor Fair Good Good

Backpressure Good Poor Good Good

Dirt Fair Poor Poor Good

Wear Fair Poor Good Good

Water Hammer Poor Good Poor Good

Freezing Good Good Poor Good


David M. Armstrong


Armstrong PromiseArmstrong PromiseArmstrong PromiseArmstrong Promise

We provide intelligent system solutions that improve utility performance, lower energy consumption, and reduce environmental emissions . . . while providing

an “enjoyable experience”!

Intelligent System Solutions S T E A M • A I R • H O T W A T E R


David M. Armstrong

®


David M. Armstrong


©2008 Armstrong International, Inc.

Documents

©2008 Armstrong International, Inc. Basic Steam Trap Operation