AQUA PLUS
Connecting to a low-pressure steam boiler
Special considerations
When designing steam and domestic hot water systems, there are some key issues that must be taken into consideration during the initial de- sign phase. By designing the system properly from the start, you can avoid problems and have a hot water loop in a steam boiler system.
•The domestic water demand should preferably not exceed 1/3 of the steam boiler capacity. Larger demand may cause difficulty obtaining steam as needed.
•Keep the loop temperature below the flash point. Flashing can result in noise and circulator damage or shortened life.
•Be sure the loop is completely closed, with no automatic or manual air vents, or anything that could allow air to enter the system when the pump shuts off.
•Pipe supply from one side of the boiler, return to the opposite side as shown.
•Supply from a tapping that is high enough to prevent introducing sediment into the piping and circulator yet still below the water line. Avoid the mud leg of the boiler.
•Use an all bronze circulator.
•Avoid wet rotor circulators. Select a circulator with a large volute, such as a typical
•This will reduce clogging and will resist the corrosion potential from the steam condensate.
•Make sure the circulator is properly sized. If the circulator runs too far out on its curve, cavitation potential increases significantly.
•Use (2) flow / check valves as shown to reduce the potential for gravity circulation.
•DO NOT use
Installation and
1.See Figure 16, page 19, for suggested piping schematic.
2.Pipe the domestic water connections to the water heater per “Do- mestic water piping,” page 6.
Boiler connections for the water heater must be below the water line. DO NOT use the gauge glass tapping or a low water
For steam piping, refer to the steam boiler manual.
DO NOT install an air vent anywhere in the piping. The piping must be air tight.
3.Wire the water heater and circulator to the boiler per suggested wiring in Figure 15. The water heater must be wired and ready to operate before proceeding. Note that the L4006A aquastat is located in the boiler and sets a boiler operating temperature when there is no call for steam heating.
To fill the boiler and water heater:
1.Follow the procedure given in Figure 16, page 19 to fill the water heater piping.
2.Follow the boiler manual instructions to fill the steam boiler.
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Figure 15 Typical wiring for connection to low- pressure steam boiler
Install the Honeywell L4006A aquastat in the boiler, be- low the water line. Set for a temperature of 180 to 190°F to control boiler temperature when there is no call for steam heating.
Valve 7, the memory stop valve, must be supplied, piped and adjusted as in- structed. This valve allows cooler return water to mix with the hot water from the steam boiler. The valve is set to yield approximately 180°F water entering the circulator. Higher temperature water could cause cavitation in the circulator, damaging the impeller and shortening circulator life.
DO NOT connect the piping to the boil- er’s mud leg. This would probably cause excessive sediment to enter the water heater piping, damaging the circulator.
The strainer in the circulator suction line must be serviced regularly. NOTE that noise from the circulator is a likely sign that the strainer is restricting circulator flow, causing cavitation.
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