Daikin Applied (UK) Ltd.
REV A
– PAGE 9. SECTION 11 ADDED. 11/03/14
Page 30 of 37
Condensate Removal from Steam Coils (continued)
Vacuum breakers must be installed between the coil and the trap inlet to ensure that the
hydraulic head drains the coil when it is at atmospheric or sub-atmospheric pressure. The
vacuum breaker should respond to a differential pressure of no greater than 750pa (3in.
of water). For atmospheric returns, the vacuum breaker should be opened to the
atmosphere, and the return system must be designed to ensure no pressurization of the
return line. In vacuum return systems, the vacuum breaker should be piped to the return
line.
Discharge from the trap must flow by gravity, without any lifts in the piping, to the return
system. This must be vented properly to the atmosphere to eliminate any back pressure
that could prevent the trap from draining the coil. Where the return main is overhead, the
trap discharge should flow by gravity to a vented receiver, from which it is then pumped to
the overhead return.
Traps must be designed to operate at maximum pressure at the control valve inlet and
sized to handle the full condensate load at a pressure differential equal to the hydraulic
head between the trap and coil. Since the actual condensate load can vary from the
theoretical design load because of the safety factors used in coil selection and the fact
that condensate does not always form at a uniform steady rate, steam traps should be
sized according to the following:-
0-15pisg (0-100kPa above atm.)
at the control valve inlet:-
Size the trap for twice the full condensate load (coil condensing rate at maximum design
conditions) at 0.5psi (3kPa) pressure differential.
16-30psig (110 to 200kPa above atm.)
at the control valve inlet:-
Size the trap for twice the full condensate load at 2psi (14kPa) pressure.
31psig (210kPa above atm.)
and over at the control valve inlet:-
Size the trap to handle triple the full condensate load at a pressure differential equal to
half the control valve inlet pressure.
The steam supply must be drained of any entrained condensate prior to entering the
coil, preferably just before the regulating valve.
Plate Heat Exchangers
