Steam Distribution Systems; Steam Piping Mains; Steam Traps - Honeywell AUTOMATIC CONTROL Engineering Manual

CHILLER, BOILER, AND DISTRIBUTION SYSTEM CONTROL APPLICATIONS

STEAM DISTRIBUTION SYSTEMS

STEAM PIPING MAINS

Steam piping mains must carry steam to all parts of the
system allowing a minimum amount of condensate (heat loss)
to form, must provide adequate means to collect the condensate
that does form, and must prevent water pockets that can cause
water hammer.
Figure 102 shows typical connections at the boiler. The
system shown uses a condensate (receiver) tank and pump.
Condensate returns must be properly pitched for gravity
condensate flow and properly insulated so heat contained in
the condensate is not wasted.
RELIEF
VALVE
CONDENSATE F & T
TRAP
RETURNS
{
HIGH LEVEL
"SPILL"
RECEIVER
TANK
PUMP
STOP
CHECK
VALVE
VALVE
SOLENOID
BLOWDOWN
VALVE
(OPTIONAL)
Fig. 102. Typical Boiler Connections.

STEAM TRAPS

Traps remove condensate from the steam mains and all steam-
using equipment without allowing steam to enter the return
mains. The thermostatic trap (Fig. 103) is most common for
trapping condensate from radiators and convectors in low
pressure systems. When the thermostatic element senses steam
temperature, it closes the valve. The valve remains closed until
the element cools.
INLET
Reprinted by permission from the ASHRAE Handbook—
1996 Systems and Equipment
Fig. 103. Thermostatic Trap.
ENGINEERING MANUAL OF AUTOMATIC CONTROL
STOP
VALVE
STEAM
MAIN
PRESSURE
CONTROLS
STEAM
F & T
BOILER
PRESSURE
TRAP
GAUGE
LOW WATER
CUTOFF, PUMP
CONTROL AND
GAUGE GLASS
TO
RECEIVER
TANK
VALVE
C2923
THERMOSTATIC
ELEMENT
VALVE
OUTLET
M15070
The float and thermostatic trap (Fig. 104) can handle large
amounts of air and condensate and is commonly used on steam
coils in air handling systems. In this trap, the thermostatic
element passes air until it senses steam at which time it closes
the valve. As condensate water builds up in the trap, the float
valve opens to discharge condensate into the return line.
THERMOSTATIC
DISC ELEMENT
FLOAT
Reprinted by permission from the ASHRAE Handbook—
1996 Systems and Equipment
Fig. 104. Float and Thermostatic Trap.
Another common trap is the inverted bucket (Fig. 105) which
has a large capacity (up to 55,500 lb/hr) for discharging
condensate. In the bucket trap, the bucket is normally down so
the valve is open. The bucket is normally about two-thirds full
of condensate so, when condensate enters the trap, it flows
around the bucket and through the trap. As air or steam enters
the bucket, the bucket rises, closing the valve when the
condensate level drops to about one-third full. Air escapes
slowly through the air vent and steam condenses so the bucket
drops, opening the outlet.
Reprinted by permission from the ASHRAE Handbook—
1996 Systems and Equipment
Fig. 105. Inverted Bucket Trap.
Kinetic traps, shown in Figures 106, 107, and 108, are used
in high pressure systems. They rely on flow characteristics of
steam and condensate and on the fact that condensate
discharging to a lower pressure contains more heat than
necessary to maintain its liquid state.
370
VALVE
INLET
OULET
FLOAT
VALVE AND
ORIFICE
M15071
OUTLET
VALVE AND
ORIFICE
AIR
INLET
M15072