MV100 ELECTRIC CONTROLLERS T100, T200 THERMOSTATIC CONTROLLERS AND V2000 RADIATOR VALVES

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.

 

MASTER ZONE

 

THERMOSTAT

1

L6006C

L1

(HOT) 24 Vac

L2

LOW VOLTAGE RELAY

PRIMARY

CONTROL

1 POWER SUPPLY. PROVIDE DISCONNECT MEANS AND

OVERLOAD PROTECTION AS REQUIRED.

M7536A

 

Fig. 23. Holding circuit for use with L6006 when verifying zero psig steam pressure.

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