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MV100 ELECTRIC CONTROLLERS T100, T200 THERMOSTATIC CONTROLLERS AND V2000 RADIATOR VALVES
11 62-3048—2
NOTE:
— While the T100 is satisfied, the V2042H is closed
and the radiator remains airlocked. Thus, no
steam can enter the radiator. The airlocked
condition remains until the T100 calls for heat, at
which point the system operates as described in
steps 1 through 6.
— An improperly cycled boiler causes either
excessive heating or lack of heat, depending on
the system time constant.
Bringing the Steam Pressure to Zero psig
To assure the proper operation of any single-pipe steam
system, ensure that the steam pressure is brought to zero at
some time during the off-cycle. One suggested procedure
follows:
1. Determine if steam is required using one of two
methods:
a. A thermostat in a representative zone controls the
valve or cycles the boiler.
b. A timing device cycles the boiler for varying lengths
of time in response to outdoor temperature.
IMPORTANT
When cycling the boiler from a space thermostat in a
zone, do not apply a radiator valve to that radiator.
2. Turn off the steam and allow system pressure to drop to
zero. Do this using one of two methods:
a. Turn the boiler off and allow the total steam pressure
in the system to drop to zero.
IMPORTANT
Before applying controls to turn a boiler on and off,
check the manufacturer recommendations.
b. In installations where turning the boiler off at the end
of each cycle is undesirable, install a control valve
(such as a Honeywell V5011 Valve) on the boiler dis-
charge line.
NOTE: Install the valve on the boiler side of the condensation
takeoff to ensure that the condensation can return to
the boiler.
3. Verify that the steam pressure has returned to zero.
Verification
Verification is necessary to prove that the pressure has
returned to zero. Simply turning off the boiler or shutting off the
steam supply does not ensure zero steam pressure. The
simplest way to check for zero pressure follows:
1. Install a strap-on Aquastat® Controller, such as the
Honeywell L6006C Aquastat® Controller, on the
condensation return line (see Fig. 19).
2. Set the Aquastat® Controller at about 150°F (66°C).
With the return line at or below this temperature, the
water is all condensation, and the pressure is
functionally zero.
3. Wire the Aquastat Controller into the interrupting circuit
to ensure that steam flow cannot resume until the
condensation line is below the setpoint. The 150°F
(66¡C) setpoint serves as a nominal starting point and
can require adjustment for individual steam systems.
Fig. 23. Holding circuit for use with L6006 when
verifying zero psig steam pressure.
L1
(HOT)
L2
1
1
LOW
VOLTAGE
RELAY
PRIMARY
CONTROL
24
Vac
L6006C
MASTER ZONE
THERMOSTAT
POWER SUPPLY. PROVIDE DISCONNECT MEANS AND
OVERLOAD PROTECTION AS REQUIRED.
M7536
A