Retrotec USACE - Manual (Page 189)

Appendix D D59
D.4.1.27 Use of Pressure-Reducing Valve to Provide Pressure
Reductions (Ineffi ciency)
Figure D102. Steam pressure-reducing valve
drops pressure from main distribution pressure
(above) to lower value suitable for building
equipment (left).
In most steam systems, steam is generated in the boiler at high pressures.
The high pressure pushes the steam energy to points of use throughout the
steam heating system. The equipment that uses the steam for heating or
other purposes is designed for a specifi c entering steam pressure, which
would be lower than the boiler pressure minus the pressure loss getting
the steam to these use points. A pressure-reducing valve (PRV) is used to
adjust the steam pressure to the desired lower value (Figure D102). This
valve allows steam to pass through an opening into a larger volume, thus
reducing the pressure. In doing so, some energy is lost. If a large pressure
drop is required, a steam turbine could replace the PRV, thereby using the
energy that would be otherwise wasted. Another option would be to look
at the total steam system to determine whether the boiler pressure could
be reduced.