PowerPoint Presentation®
What MUST a Steam Trap do?
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Minimize steam lose
Air Venting
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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
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Mechanical
Use difference in density between steam and condensate to operate valve. A float operates the valve.
Thermodynamic
Thermostatic
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Must sub-cool deeply to prevent steam loss
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Good for use in super-heated applications.
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Trap body
Disk bonnet
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Full capacity flow
Two pressure drops
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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 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
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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
Disk Wear
Seat Wear
Flat valve and seats require near perfect flatness to seal
Two seats to seal
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Bellows cold; vent open to air and/or condensate flow
Condensate flow decreases
Valve modulates to balance outlet flow = inlet flow
Steam enters; steam air mixture closes vent; temperature below saturation
Start-Up
Modulating
Steam lost with air removal
Dirt falls to bottom; may stop ball from dropping holding valve open; may plug valve
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Air Vent
Inlet
D
C
B
A
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IB At Start-Up
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
Low velocity flow
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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
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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
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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
Small dirt flushed
Valve wide open
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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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Bellows Balance
Modulation