Differential pressure modulated gas valve for single stage combustion

Abstract

An apparatus senses the pressure changes in a collector box or relief box of a furnace due to changing wind conditions, and adjusts the gas flow accordingly. The apparatus controls the main gas valve of the furnace through a regulator loop. The regulator loop has a first port that communicates with a chamber below the main diaphragm of the valve, and a second port that communicates with a chamber above the main diaphragm. The regulator includes two diaphragms linked rigidly. A feedback pressure channel is connected to the collector box or the relief box, at one end, and to a feedback pressure tap at the other end. An increase in wind at the furnace vent causes changes in pressure in the collector box and the relief box. This change in pressure is delivered to the feedback pressure tap. When the pressure at the feedback pressure tap increases, the top diaphragm and the bottom diaphragm both move upward. As the pair of diaphragms move upward, there is relatively more flow through the second port and relatively less through the first port, causing a pressure differential across the main diaphragm; a higher pressure then exists above the main diaphragm compared to the pressure below the main diaphragm. The main valve then moves toward the closed position. When the pressure at the feedback pressure tap decreases, the diaphragms move down. This causes relatively more flow through the first port and relatively less flow through the second, causing the valve to open.