5
Thermal#Expansion
Determine(if(a(check(valve(exists(in(the( inlet(
water(line.(Check(with(your(local(water(utility.(
It(may(have(been(installed(in(the(cold( water(
line(as(a(separate(back(flow(preventer,(or(it(
may(be(part(of(a(pressure(reducing(valve,( water(
meter(or(water(softener.(A(check(valve(located(
in(the(cold(water(inlet(line(can(cause( what(is(
referred(to(as(a(“closed(water(system”.(A(cold(
water(inlet(line(with(no(check(valve(or( back(
flow(prevention(device(is(referred(to(as(an(
“open”(water(system.
As(water(is(heated,(it(expands(in(volume( and(
creates(an(increase(in(the(pressure(within(
the(water(system.(This(action(is(referred(to(
as(“thermal(expansion”.(In(an(“open”(water(
system,(expanding(water(which(exceeds(the(
capacity(of(the(storage(tank(flows(back(into(
the(city(main(where(the(pressure(is(easily(
dissipated.(
A(“closed(water(system”,(however,(prevents(
the(expanding(water(from(flowing(back(into(
the(main(supply(line,(and(the(result(of( “thermal(
expansion”(can(create(a(rapid(and(dangerous(
pressure(increase(in(the(storage(tank(and(
system(piping.(This(rapid(pressure(increase(can(
quickly(reach(the(safety(setting(of(the(relief(
valve,(causing(it(to(operate(during(each(heating(
cycle.(Thermal(expansion,(and(the(resulting(
rapid(and(repeated(expansion(and(contraction(
of(components(in(the(storage(tank(and(piping(
system(can(cause(premature(failure(of(the(relief(
valve,(and(possibly(the(heater(itself.(Replacing(
the(relief(valve(will(not(correct(the(problem!
The(suggested(method(of(controlling(thermal(
expansion(is(to(install(an(expansion(tank(in( the(
cold(water(line(between(the(storage(tank(and(
the(check(valve((refer(to(the(illustration(on( the(
page(8).(The(expansion(tank(is(designed(with(
an(air(cushion(built(in(that(compresses(as( the(
system(pressure(increases,(thereby(relieving(
the(over(pressure(condition(and(eliminating(the(
repeated(operation(of(the(relief(valve.(Other(
methods(of(controlling(thermal(expansion(
are(also(available.(Contact(your(installing(
contractor,(water(supplier(or(plumbing(
inspector(for(additional(information(regarding(
this(subject.
Inspect#Storage#tank
Inspect(the(storage(tank(for(possible(damage.