PVI Industries U-TUBE SINGLE-WALL PV500-34 - Manual (Page 4)

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PV500-34 05/03 Section 34 4
STEAM WITH SINGLE-WALL / DOUBLE-WALL (con't)
STEAM VALVES
1. One or more two-position, on-off, electric
valves are used to control the flow of steam.
The valves will return to the closed position
when power is off. This feature will prevent an
excessive temperature buildup in the event of
a power failure. The valve manufacturer’s
operation and maintenance instructions are
shipped with the unit. Refer to these
instructions during start-up and file for future
referencing on maintenance.
CAUTION
Most valve problems are caused by dirt or
trash in the steam line. This is most likely to
occur during installation. Teflon pipe tape,
pipe joint compounds, metal particles and dirt
will clog up strainers and orifices and prevent
valve seats from closing. Clean all pipe line
strainers at start-up and check the valves
again after a few days operation as
recommended by the valve manufacturer.
Inspection of strainers and blowdown piping
should be part of the normal maintenance
routine on this equipment.
OPTIONAL SAFETY SYSTEMS
1. This heater may be supplied with a pressure
gradient monitoring (PGM) system,
consisting of a differential pressure switch, a
delay timer and a steam purge valve. It
serves as a safety system to prevent the
contamination of potable water with steam.
The pressure switch monitors both steam
and potable water system pressure. If the
potable water pressure falls to a point
slightly above the steam pressure and stays
there for a short period of time, then the
heater shuts down, closes the steam valve
and opens a steam purge valve to quickly
reduce the steam pressure in the heat ex-
changer. The system requires a manual
reset to begin operation again. Note that
the system does not necessarily detect a
leak, but it prevents steam from entering the
potable water if there is a leak.
2. Another safety option is the tank purge
system (sometimes called a double solenoid
safety system). The tank temperature is
monitored and if it exceeds an adjustable
limit, the heater is shut down and a valve
opens to dump the overheated water. This
allows cold make-up water to enter the tank
and quickly reduce the tank temperature.
START-UP OPERATION
1. After all the steam, condensate and water
lines are installed and inspected, the steam
supply source and the condensate receiver
should be checked for correct operation.
Steam supply pressure to the heater must be
equal to or less than the supply pressure on
the heater decal. A pressure reducing valve
can be installed in the supply line to meet this
requirement.
2. Steam is directed to the heat exchanger
through a header and steam control valves.
The steam control valves are normally closed,
on-off, electric valves and solenoid-operated.
Should an electrical power failure occur,
steam valves will close and stop steam flow to
the unit.
WARNING!
Excessive steam pressure can cause the
steam valve(s) and condensate trap to
malfunction and can cause the heat transfer
rate to exceed the relief valve capacity which
can result in an explosion causing damage,
injury or death.