Vent Proving Switch

The v p s vent proving switch is the latest innovation in combustion safety from field controls. The BPS is an electronic limit control for use with gas fired category one appliances such as furnaces, boilers, and water heaters equipped with a draft hood. The VPS ensures proper operation of these non condensing negative vented appliances by monitoring their vent gas temperature and will shut the appliances main burner off to prevent spillage of combustion products into the home. A condition known as back drafting. The VPS is installed in the appliance vent downstream of the draft hood. When installed with a field controls GVD vent damper, the VPS wire harness assembly allows for seamless electrical connection with the appliance safety circuit. Let's look at this type of installation and how the system works. When the appliance is idle, the VPS is in standby mode. The GVD is closed and there is no flow through the vent. When the thermostat calls for heat, The VPS starts its six minute vent proving timer and signals the GVD to open while monitoring the vent gas temperature. Upon proving open, the GVD signals the appliance that it is safe to fire its main burner. The appliance's main burner fires. Products of combustion flow from the appliance and into the vent. The vent gas temperature increases as the appliance achieves steady state operation and the VPS monitors this temperature, allowing the appliance to continue firing when it exceeds one hundred sixty five degrees. Up until this point, the home has a neutral pressure relative to the outdoors. If the pressure in the home becomes negative during appliance operation, As a result of turning on an exhaust fan, for example, the appliance vent can back draft. The VPS is monitoring the vent gas temperature. And will detect that it is decreasing as the cooler outside air is pulled down the vent. When the temperature reaches one hundred forty five degrees, The VPS will go into a soft lockout. Open its proving circuit, causing the appliance to shut off its main burner and the GVD to close. A red indicator light will illuminate during the lockout period. The VPS lockout period is one hour. After which it will allow the appliance to refire if there is still a call for heat present. Because back drafting is often a temporary condition, The VPS will repeat this sequence until proper venting is established. While most gas fired atmospherically vented appliances have blocked vent switches. These are not designed to detect back drafting. As homes are made tighter to save energy. The potent issue of back drafting due to depressurization increases. The VPS vent proving switch protects the home and its occupants from back drafting for greater safety. To learn more, contact field controls today.