AUTOMATIC STEAM PRESSURE RELIEF VALVES

After a boiler has been engineered, built and tested for a given operating pressure, there is only one reliable way to prevent operation of the boiler above this design pressure.  That is with a safety valve.  The safety valve should be sized so that a single valve can handle the maximum steam production rate of the boiler and, once open, prevent boiler pressure from continuing to rise.  Standard operating procedure for the last century has been to install two safety valves on the boiler, one set 3-5 lbs below the design pressure and one valve set at design pressure. 

The valves listed below will fulfill this requirement for almost any model boiler.  SVL3 and SVL4 are designed for small table top boilers operating around 40 PSI, such as the small Stuart boilers. SVL1 is designed for boilers up to small 1 1/2” scale locomotives, operating at 100 PSI.  All three are adjustable for release pressure and have a “pop” action.  The pressure differential is not adjustable on these valves.  If the valves are operated above their nominal pressure, the set-reset differential increases.  If operated at lower pressure, the differential decreases to the point of disappearing about 10-15% below nominal pressure.

SVL2 is a much more complex valve, being a true adjustable differential pop valve.  The differential is adjusted through the differential ring lock screw hole, from 3 PSI to whatever the operator desires.  The increment is approximately 3 psi per slot in the differential ring.  The pressure of the valve can be adjusted from 40 PSI to as high as 200 PSI.