For distribution pressures below 50 psi, the pressure regulating valve may
3 . 2 Dual Valve Installations. I n relatively large installations with steam
requirements above 3,000 pounds per hour, and where variations in steam demand
a r e likely to occur, a dual valve installation is used. T h i s i n s t a l l a t i o n
consists of two reducing valves installed in parallel, sized to pass 70 and 30
percent of maximum flow. The larger valve should be set at a slightly reduced
pressure so that it will remain closed as long as the smaller valve can supply
the demand. This prevents wire-drawing of seats and valves of large reducing
valves operating at very low loads. For example, if a total of 40,000 pounds
of steam per hour are required, the larger valve would be sized for 0.70 x
40,000, or 28,000 pounds per hour; the smaller one would be sized for 0.30 x
40,000, or 12,000 pounds per hour.
4 INSPECTION AND MAINTENANCE OF PRESSURE REDUCING STATIONS I n addition to
the procedures addressed in chapter 6, sections 2 and 3, perf o r m the following
Report any malfunction in the operation of any instrument of gauge.
P r o t e c t gauges from violent pressure fluctuations by throttling the
gauge needle valve or by installing snubbers.
Clean gauge glasses as required for ease of reading.
Ensure steam lines are drained of condensate.
Blow down all strainers and clean strainer baskets at regular
i n t e r v a l s , as required.
A l l o w only authorized and trained personnel to repair, calibrate,
o r adjust pressure reducing stations.