Vulcan-Hart MHB24G, VHX24G5 manual VHX Series Steamer Electrical Operation

VHX SERIES STEAMER - ELECTRICAL OPERATION

3.Water level reaches LLCO (low water level cut- off) probe for the water level control and to the auxiliary LLCO probe for the auxiliary low level cut-off control.

A.LLCO relay energizes, LLCO contacts (N.O.) CLOSE and LED lights.

NOTE: No power is transferred until ignition sequence starts.

B.Aux. LLCO relay energizes, LLCO contacts (N.O.) CLOSE and LED lights.

NOTE: The LLCO and aux. LLCO relays will remain energized and LLCO LED’S will remain lit until the water level drops below the LLCO probes or the power switch is turned OFF.

4.Water reaches LL (low level) probe.

5.Water reaches HL (high level) probe.

A.Fill solenoid is de-energized.

6.Press the manual reset switch.

A.Relay coil (R1) energized.

1)High pressure light turns OFF.

B.Relay coil (R3) energized.

1)Low water light turns OFF.

2)Transformer (T1) energized.

7.24VAC is connected through the cycling pressure switch contacts to the following components:

A.Normally open (N.O.) side of the air pressure switch.

NOTE: No power is transferred until air pressure switch CLOSES.

B.Relay coil (R2) is energized and R2 contacts (N.O.) CLOSE.

1)120VAC is supplied to the combustion air blower and blower starts.

C.Once the combustion blower develops sufficient pressure, the air pressure switch

CLOSES.

1)24VAC is then applied to the Ignition control module and the ignition cycle starts.

a.Pilot voltage (PV) N.O. contacts

CLOSE.

b.Pilot gas valve energized, pilot valve opens for gas to flow and Ignitor begins sparking to light pilot.

2)Pilot ignition is established (pilot lit) and a micro amp flame "sense" current is sent back to the ignition module through the ignition cable.

3)Main voltage (MV) N.O. contacts

CLOSE.

a.Main gas valve OPENS, burner lights and boiler begins to heat up.

NOTE: As boiler heats up and builds pressure, some by-pass water/steam is produced which runs into the steam drain box. This causes the cold water condenser (CWC) solenoid to cycle, cooling the drain water and condensing any steam vapors before exiting the drain. The CWC solenoid is powered by the CWC thermostat.

NOTE: On initial cold startup only, the boiler pressure may overshoot and cause the mechanical pressure relief valve to OPEN momentarily.

b.As long as the ignition control module senses a burner flame, the internal main voltage (MV) contacts (N.O.) on the ignition module remain closed, and main gas valve stays ON.

c.If sparking is allowed to continue for a total of 90 seconds, then the ignition module locks out power to the gas valve (pilot valve and main valve remain closed). The module remains locked out until the power switch is turned to OFF then ON and the manual reset switch is pressed to re-start the ignition trial cycle.

8.Boiler steam pressure reaches upper limit set point of 10 PSI (approximately 15 min).

A.Cycling pressure switch opens and power is removed from the following components:

1)Combustion air pressure switch normally open (N.O.) terminal.

2)Relay coil (R2) returning R2 contacts to there N.O. shelf state.

a.Combustion air blower de- energized.

B.Ignition control module is de-energized, PV and MV contacts OPEN.

1)Main gas solenoid valve de- energizes, gas flow shuts OFF and burner goes out.

9.Boiler steam pressure drops below lower limit set point of 8 PSI and the cycling pressure switch CLOSES.

A.Boiler steam pressure is maintained by the cycling of the pressure switch between the

Page 49 of 68 F24700 (October 2001)