TIP #3: Noting Seasonal Steam Load Variations is Important.Even when you think you’ve selected the correct PRV, there are some “tricky” installations that can fool you. For instance, consider an installation where a large percentage of the supply steam is used for heating and only a small percentage is used in a manufacturing process. Obviously, in such an application, the peak steam demand occurs in the winter months and the summer steam demand is greatly reduced. Seasonal two level steam load variation is often ignored. Typically, a PRV is selected to handle the peak wintertime loads and summertime needs are forgotten. Which means that during the summer months the PRV is oversized. And that of course means that (as discussed in Tip #2) the PRV will perform poorly and wear prematurely. Thankfully, there is a simple solution to the load variation problem. A single stage parallel reduction station such as the one shown in Figure 1 makes it possible to use properly sized valves in both summer and winter. Here’s an example of how it works (refer to Figure 1).
- The smaller PRV (Valve A) is sized to handle one third of the maximum output on the system.
- Pressure reducing valve B is sized to handle the remaining two thirds of the maximum load.
- Valve A is set to a slightly higher downstream pressure than Valve B. For that reason, when the load demand is low, steam will take a path through Valve A.
- As the demand increases, however, a point will be reached where the small size of Valve A begins to restrict steam flow.
- At that time, the downstream pressure will drop and steam will begin to also flow through Valve B. If the total system demand diminishes, the reverse will take place. Regardless of the level of the load, this two path system provides appropriate downstream pressure reduction while permitting each PRV to operate under conditions that promote long life and reliable performance. CONTINUE TO Prepare for a Malfunctioning PRV – Steam System Troubleshooting Tip #4 >>
Remember Seasonal Steam Load Variations – Steam System Troubleshooting Tip #3