AERCO SWDW68 U-Tube Double-Wall Heaters w/ECS - Manual (Page 84)

HE-
111 − DISASSEMBLY AND REASSEMBLY
Rev B Mar 2013 9-4
3. To replace the heat exchanger shell (13) on a DW-45 heat exchanger, skip the rest of this step and
all of step 4 and proceed to step 5. For DW-24 and DW-68 heat exchangers, proceed as follows:
a. Place a Teflon upper tubesheet release gasket (24), the shell gasket (23) and another upper
tubesheet release gasket (ALL NEW) onto the U-bend assembly flange.
b. Using a hoist or block and tackle attached to the lifting lugs (11) on the heat exchanger upper
head assembly (or to bolt holes in the shell top flange, if the upper head assembly has been
removed), CAREFULLY lower the upper head assembly and shell STRAIGHT DOWN over the
U-bend tubing assembly (14). DO NOT SCRAPE THE SHELL AGAINST THE TUBING.
c. Make sure that the shell is positioned properly by lining up the marking you put on the edges of
the flanges in 9.3, step 7.
d. Assemble the studs (10) and nuts (9) into the manifold, U-bend assembly flange and shell flange.
Cross-tighten the nuts to approximately 75 foot-pounds of torque to obtain uniform seating. Then
progressively tighten the nuts to approximately 150 foot-pounds of torque for a tight seat.
4. If the heat exchanger upper head assembly (12) has been removed from the shell (13):
a. Place a NEW shell gasket (23) onto the gasket surface of the shell top flange.
b. Replace the heat exchanger upper head assembly onto the shell top flange making sure that the
stud holes line up.
c. Reassemble the studs, lifting lugs (11), and nuts (18) into the head and shell flanges. Tighten the
nuts in the same manner as outlined in step 3d above.
d. Replace the water solenoid valve (2), the relief valve (1), and all piping. Reconnect all connecting
wiring, if any, required for accessories on the upper head assembly. Replace the thermocouple
into their proper locations in the upper head assembly.
Continue assembling the heat exchanger at step 7.
5. If you are replacing the heat exchanger shell (13) on a DW-45 heat exchanger, proceed as follows:
a. Place an upper tubesheet release gasket, the lower shell gasket (23) and another upper
tubesheet release gasket (24) (ALL NEW) onto the U-bend assembly flange.
b. Using a hoist or block and tackle attached to the lifting lugs (11) on the heat exchanger upper
head assembly (or to bolt holes in the shell top flange, if the upper head assembly has been
removed), CAREFULLY lower the upper head assembly and shell STRAIGHT DOWN over the
U-bend tubing assembly (14). DO NOT SCRAPE THE SHELL AGAINST THE TUBING.
c. Make sure that the shell is positioned properly by lining up the marking you put on the edges of
the flanges in 9.3, step 7.
d. Assemble the studs (10) and nuts (9) into the manifold, U-bend assembly flange and shell flange.
Cross-tighten the nuts to approximately 75 foot-pounds of torque to obtain uniform seating. Then
progressively tighten the nuts to approximately 150 foot-pounds of torque for a tight seat.
6. If the heat exchanger upper head assembly (12) has been removed from the shell (13):
a. Place a NEW upper shell gasket (25) onto the gasket surface of the shell top flange.
b. Replace the heat exchanger upper head assembly onto the shell top flange making sure that the
stud holes line up.