Instrument Air Consumption and Receiver Sizing
List every air user (positioners, I/P converters, actuators, purge and analysers) with its steady consumption and stroking demand. The workbook totals the demand with leakage and margin, then sizes the instrument air receiver for a hold up time.
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- Calculator sheet with a worked example
- How to Use sheet with steps
- 39 built in formulas, no macros
- Yellow input cells, grey results
- Calculation sign off block
- Excel, Google Sheets and LibreOffice
Worked Example
These are the results of the example already filled in the workbook. Replace the yellow cells with your own data.
Air users
| User | Qty | Steady each (Nm³/h) | Air per stroke each (L free) | Strokes per hour each | Steady total (Nm³/h) | Stroking total (Nm³/h) | Total (Nm³/h) | Remarks |
|---|---|---|---|---|---|---|---|---|
| Control valve positioners (digital) | 18 | 0.10 | 6.0 | 20 | 1.80 | 2.16 | 3.96 | |
| On off valve actuators | 10 | 0.00 | 25.0 | 2 | 0.00 | 0.50 | 0.50 | |
| I/P converters | 4 | 0.25 | 1.00 | 0.00 | 1.00 | |||
| Analyser shelter purge | 1 | 6.00 | 6.00 | 0.00 | 6.00 | |||
| Gas analyser (sample aspirator) | 2 | 1.20 | 2.40 | 0.00 | 2.40 |
About this Calculator
Instrument air is a safety utility: when it fails, valves go to their fail positions and the plant trips. Sizing compressors and receivers from a real list of air users, with leakage and a hold up time, avoids both nuisance trips and oversized compressors.
Basis: Free air (Nm³/h) totals with design margin; receiver volume V = t × (C − S) × Pa ÷ (P1 − P2), the drawdown method used in compressed air system guides.
How to use
- List each type of air user with quantity, steady consumption and air used per stroke from the vendor data.
- Estimate strokes per hour for modulating valves (positioner activity) and on off valves.
- Set leakage and margin allowances from your project specification.
- Enter the receiver pressure, minimum header pressure and the required hold up time.
- Use the total with margin to size compressors and dryers, and the receiver volume for the storage vessel.
Formulas used
- Steady total = qty × steady consumption.
- Stroking total = qty × air per stroke × strokes per hour ÷ 1000.
- Design demand = total × (1 + leakage) × (1 + margin).
- Receiver volume = hold time × demand with leakage ÷ 60 × Pa ÷ (P1 − P2).
Related tools
Frequently Asked Questions
How much air does a valve positioner use?
Digital positioners typically use about 0.05 to 0.3 Nm³/h at steady state; check the data sheet, as low bleed models use less.
What hold up time should an air receiver give?
It is set by the project, often 5 to 15 minutes, long enough for a standby compressor to start or for a safe shutdown.
Why allow for leakage?
Fittings, tubing and regulators leak; plants often lose 10 % or more of instrument air to leaks.
Learn more on the blog
Control valve positioner working
A practical guide on instrumentationblog.in that explains the engineering behind this workbook.
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