AERCO SWDW68 U-Tube Double-Wall Heaters w/ECS - Manual (Page 23)

HE–
111 − FUNCTIONAL DESCRIPTION
Rev B Mar 2013 3-3
COMPOUND PRESSURE
GAUGE
STEAM INPUT
SOLENOID VALVE
CONDENSATE OUT
PLUGGED DRAIN
TEMPERATURE CONTROLLER
CXT-E CONTROL VALVE
VACUUM BREAKER
PRESSURE AND
TEMPERATURE
RELIEF VALVE
CXT-E ACTUATOR
CONTROL BOX
SHELL
COLD
WATER
INPUT
HOT WATER OUTPUT
LEAK
DETECTION
PORT
RECIRCULATION
PUMP
RECIRCULATION
PIPING
OUTLET MANIFOLD
LOWER SHELL
FLANGE
UPPER SHELL
FLANGE
UPPER HEAD
ASSEMBLY
LOWER HEAD
ASSEMBLY
Figure 3-3. AERCO Double-Wall Heat Exchanger, Model DW-24
3.2.3.1 Shell and Heads
The heat exchanger body incorporates a stainless steel shell, bronze upper head and navy brass
tubesheets, forming a pressure vessel that conforms to ASME standards. The heat exchanger body
encloses the tube bundle and tubesheets.
3.2.3.2 Double-Wall U-Tube Bundle and Tubesheets
The double-wall U-bend copper tubes that conduct steam through the heater shell conform to BOCA
(National Plumbing Code), IAPMO (Uniform Plumbing Code) and NAPHCC (National Standard Plumbing
Code), the three national standards that address double-wall construction. The outer wall of each double-
wall tube is brazed to the upper tubesheet, and the inner wall is brazed to the navy brass lower
tubesheet. Any tube leakage from the air spaces between the inner and outer walls of the double-wall
tubes accumulates in the space between the bottom shell flanges which make up the bottom head. The
accumulated leakage water is discharged through the leak detection port.
3.2.3.3 Recirculation Pipe and Pump
Referring to Figure 3-3, the recirculation pipe and constant-rate recirculation pump deliver a continuous
sample of the heated output water to a 1½-inch pipe junction with the Cold Water Input pipe to regulate
steam flow at the Steam Input (see 3.3.2).
3.2.3.4 CXT-E Control Valve
The CXT-E Control Valve regulates the flow rate of steam into the heat exchanger in response to
positioning control signaling from the Temperature Controller (see 3.3.2). The CXT-E Control Valve
consists of a valve body and linkage to the CXT-E Actuator. The CXT-E Actuator is discussed in 3.3.4.5.