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To choose the correct regulator pressure range, first confirm that the regulator can accept the highest inlet pressure your system may supply. Then select an outlet range that covers the required operating pressure and provides suitable adjustment and pressure control at the expected flow.
A regulator’s maximum inlet rating and adjustable outlet range describe different capabilities. Both must match the application.
This article is Part I of ControlAir’s regulator-selection series and expands on the pressure questions in How to Determine the Appropriate Regulator.
What Is the Difference Between Inlet Pressure and Outlet Pressure Range?
| Pressure Specification | What It Means | What to Check |
|---|---|---|
| Maximum Inlet Pressure | The highest permitted supply pressure for the specified configuration and conditions. | The highest pressure the system can supply, including anticipated pressure excursions. |
| Outlet Pressure Range | The pressure adjustment range provided by the selected regulator configuration. | Normal pressure setting, required adjustment span, and performance under flow. |
| Minimum Available Inlet Pressure | The lowest supply pressure available during operation. | Whether sufficient pressure remains to deliver the required outlet pressure and flow. |
How Do You Check the Maximum Inlet Pressure?
Identify the highest supply pressure the regulator may encounter, rather than relying only on the normal compressor or line-pressure setting.
Use the published rating for the exact model, options, and operating temperature. Do not treat proof-test or burst-pressure information as permission to operate above the maximum inlet rating.
Configuration can change the limit. For example, ControlAir’s Type 330 lists a maximum supply pressure of 250 psig for manual-drain models and 150 psig for automatic-drain models.
Confirm the ratings of connected equipment as part of the complete installation.
How Do You Choose the Outlet Pressure Range?
Start with the normal required outlet pressure and the full span of settings the application will use.
For many spring-loaded regulators, a range that closely matches the application can provide better adjustment resolution than an unnecessarily broad range. Resolution describes how finely the operator can adjust pressure.
ControlAir’s general starting guideline is to place the normal operating pressure at approximately 50–80% of the selected range. Confirm the final choice against the specific regulator’s capabilities and flow curves.
Example: Selecting a Range for 45 psi Output
If an application normally requires 45 psig, a 0–60 psig range places that setting at 75% of the range.
A 0–120 psig model also includes 45 psig, but may provide less convenient fine adjustment. The wider range may still be appropriate if the application requires substantially higher settings at other times.
The final selection should satisfy the complete operating range and maintain acceptable outlet pressure at the required airflow.
Why Does the Range Spring Affect Regulation?
In a spring-loaded pressure regulator, the adjusting mechanism changes spring force, which is balanced against pressure forces inside the regulator.
Changing the spring range can therefore change adjustment resolution and pressure-versus-flow behavior. Do not assume that two ranges of the same regulator perform identically at a shared pressure setting.
Review the manufacturer’s data for the selected range rather than choosing the highest available range by default.
How Do Flow Curves Help Confirm Your Selection?
A flow curve shows outlet pressure on the vertical axis and flow rate on the horizontal axis. It helps determine whether a regulator can maintain an acceptable pressure as downstream demand changes.
The illustrated curves show outlet pressure falling as flow increases, a behavior called droop. The curves also use different initial settings and supply conditions, so they should not be treated as a controlled comparison of spring range alone.
To evaluate your operating point:
- Identify the curve for the applicable model, range, and supply conditions.
- Find the required flow rate on the horizontal axis.
- Read the corresponding outlet pressure.
- Check whether that pressure is acceptable throughout normal and peak demand.
For more detail, read Pressure Regulator Cv: Flow Curves and Proper Sizing.
What If the Application Needs a Wide Adjustment Range?
Confirm performance at both the lowest and highest required settings. A range that includes every setting may still provide different adjustment sensitivity or flow performance across that span.
ControlAir’s original selection guidance recommends avoiding the upper and lower 10% of the adjustment range when practical. Treat this as a general selection guideline, not a replacement for model-specific specifications.
What Information Should You Provide When Selecting a Regulator?
- Maximum and minimum available inlet pressure.
- Normal outlet setting and full required adjustment range.
- Normal and peak flow demand.
- Acceptable outlet-pressure variation.
- Operating medium, temperature, and installation requirements.
Pressure selection is one part of regulator sizing. Continue with Choosing the Correct Regulator: Part II – Media, or contact [email protected] for help reviewing your application.