Pressure reducing Valves are found on many standpipe systems and there are dozens of types of these valves.  This blog post will show only a few so be sure to familiarize yourself with the ones found in your response area.  Pressure reducing valves are designed to regulate the pressure at a given standpipe outlet.  Pressures can be very high when dealing with fire pumps or gravity tanks.  These valves are intended to prevent over pressurization of components after the valve.  By reducing pressure flow is also reduced. 

The best and easiest way to deal with a pressure reducing valve is to remove it completely.  One style of pressure reducing valve threads onto the standpipe outlet.  When this type of valve is found, remove it with a spanner or pipe wrench and proceed as normal.  If the valve can not be removed you may have to go to the floor two floors below the fire and hook up there.  If you are unable to remove any of the pressure reducing valves, ensure the valve is in the full open position and proceed with caution. 

Some standpipe outlet valves have a pressure reducing device built into them.  Some of them can be adjusted with a screwdriver or allen wrench and others require disassembly of the valve and special tools.  These are the pressure reducing valves that firefighters must be intimately acquainted with before the fire to ensure a successful operation.