Twin-stage propane regulators are a combination of both first and second stage regulators assembled into one unit. Integral twin stage regulators are always installed at the tank and compensate for varying tank pressures on the inlet side and deliver steady service line pressure compensating for varying appliance demand on the outlet side. Integral twin stage regulators are used in propane vapor service only and are the most common type of regulators used in residential propane gas installations.
Unlike two-stage systems, integral twin-stage propane regulators are able to deliver propane to appliances at required pressure through one single regulator assembly. Pictured below is an integral twin stage regulator, often referred to as just a "twin-stage regulator". It incorporates all the functionality of two separate regulators and is primarily used when the gas service line to the house or appliance covers a short distance and BTU load requirements are not extremely high. The first stage side consists of the regulator inlet and is connected to the pigtail at tank pressure. As gas enters the high pressure side of the regulator it is immediately lowered and delivered to the second stage side at a lower pressure. The second stage side of the regulator then lowers the pressure to about 11" water column. Following these two subsequent stages of pressure reduction, the gas is delivered through the outlet, into the gas service line, and finally to the appliances downstream.
The use of an integral twin stage regulator is primarily limited to residential applications and similar applications where extremely high BTU requirements are not a factor. In gas systems where this type of regulator is installed, it is important to know that this is the only pressure regulation device between the tank and the house or structure being serviced. If your propane company recommends replacing the regulator, take this suggestion very seriously. Although twin stage regulators are designed to commonly handle less than one million BTU/hr, they are not to be installed on small cylinders. All propane tank regulators are to be installed by licensed propane gas professionals.