Pressure Reducing Valves Part Three: Factors that a User Can Control to Minimize OffsetJuly 1, 2016 by admin
In our last blog post, we discussed the factors that influence offset, and the amount of that offset. Some of those factors are intrinsic to all regulator designs, and cannot be controlled by the user. However, some can be controlled by the regulator design selected and it’s specific features. In this blog post, we will discuss factors that a user can control during commissioning to lower offset.
Factors that the user can control during regulator commissioning to lower offset. (How to minimize offset in an existing installation):
Set your regulator at flowing conditions! If you bench set a regulator in the shop at a low flow rate and install it on an installation with higher flow rates than your test bench, the regulator set point will droop lower at the higher flow rate. Set the pressure in your installation following these guidelines.
Applications with stable flow rates:
- Example: Stable clean compressed air and gas pressure control: For stable sparge, or continuous blanket gas flows, set the installed regulator at your normal flow rate. It will remain at that set point! Another benefit is that you don’t need a more expensive larger process type regulator. A small gas regulator (Figure 1 below) will usually work fine and be accepted by most pharma E&C’s and end users. The only exception to that rule would be if the regulators set point is below 5 psi, as a larger diaphragm can help with set point stability at lower pressure settings. (future blog topic).
- Example: Stable ambient WFI, or USP Purified Water Point of Use Pressure control: For pressure reduction for stable ambient WFI points of use (filling a formulation vessel with WFI for example), set the outlet set point at that filling flow rate. If you do, the pressure will not vary during filling. Note that for this particular application, your customers will usually require that you provide a process type regulator (See Figure 2 below) for drainability reasons.
Applications with variable flow rates – Example: Clean Steam for SIP pressure/ temperature control:
- Set the regulator (Figure 2 below) with steam flowing at a mid to high flow rate to minimize the total variance in offset during operation. Look at the blue curve in the air flow offset chart below -Exhibit 1. If you set the regulator at 880 scfh* the maximum offset you will experience at your maximum flow of 1800 scfh (during heat up for example) for is about 1.5 psi. The same is true when the flow decreases substantially during Temperature Hold.
In our next blog post, we will discuss additional factors that you can control during project design and specification to reduce offset.
Karl Lutkewitte, Steriflow Valve Sales and Product Manager