Calculator Inputs
Formula Used
Active pipes = Speaking stops drawn × Maximum simultaneous notes
Base airflow = Active pipes × Average airflow per pipe
Leakage airflow = Base airflow × Leakage percentage
Reserve airflow = (Base airflow + Leakage airflow) × Reserve percentage
Corrected airflow = Gross airflow ÷ Air density ratio
Total pressure = Pipe pressure + Trunk loss + Reservoir loss + Filter loss
Horsepower = (Corrected CFM × Total pressure) ÷ (6356 × Efficiency)
Suggested motor horsepower = Shaft horsepower × Motor service factor
How to Use This Calculator
Enter the number of stops likely to draw wind at the same time. Add the highest realistic number of simultaneous notes. Use measured pipe airflow when available. Enter wind pressure and pressure losses in inches of water. Add leakage and reserve margins for practical service conditions. Then press calculate.
Example Data Table
| Example | Stops | Notes | CFM per Pipe | Pressure | Leakage | Reserve | Use Case |
|---|---|---|---|---|---|---|---|
| Small chamber organ | 6 | 3 | 0.25 | 3.5 | 10% | 20% | Light support |
| Medium church organ | 12 | 5 | 0.35 | 4.5 | 12% | 25% | General booster sizing |
| High demand division | 18 | 6 | 0.55 | 6.0 | 15% | 30% | Reeds or heavy chorus |
Understanding Pipe Organ Booster Blower Sizing
A pipe organ needs steady wind before any pipe can speak clearly. The main blower often handles normal playing. A booster blower helps when long ducts, added divisions, rebuilt chests, or higher wind pressures create extra demand. Sizing the booster is not only a matter of guessing motor power. It should start with airflow, pressure loss, leakage, and reserve margin.
Why Airflow Matters
Airflow is the volume of wind needed while notes are sounding. This calculator estimates active pipes from stops drawn and simultaneous notes. It then multiplies that number by average pipe demand. Large reeds, bass pipes, and high pressure ranks may need more wind than small flue pipes. For that reason, the average pipe airflow input should be adjusted after shop measurements.
Pressure and Losses
Pipe organ wind pressure is often measured in inches of water. The blower must overcome the required pipe pressure plus losses in trunks, bends, filters, reservoirs, and expression boxes. Small pressure losses can matter in an organ because wind stability affects speech, tuning, and tremulant behavior. A booster should deliver the needed flow without making the system noisy or unstable.
Using Safety Margins
Leakage and reserve values protect the design from real world conditions. Old leather, pallet gaps, conductors, and chest valves can leak air. A reserve margin allows strong musical passages without starving the wind system. Too little reserve can cause sagging pressure. Too much blower may cause control problems, noise, and wasted power.
Reading the Output
The final result shows corrected airflow, total pressure, estimated shaft horsepower, suggested motor horsepower, and any margin against an existing blower. These numbers are planning estimates. A final installation should still be checked with a manometer, anemometer, and careful listening at the organ. Use the output to compare options, document assumptions, and discuss improvements with an organ technician.
Practical Setup Notes
Enter conservative values when records are missing. Measure wind at the chest, not only near the blower. Check the trunk path for sharp turns and undersized channels. Keep the booster isolated with suitable controls when needed. Good layout reduces turbulence, heat, vibration, and sudden pressure swings during demanding passages. Record each assumption before comparing final blower upgrade choices.
FAQs
What does a pipe organ booster blower do?
It adds wind capacity when the main blower cannot maintain stable pressure for certain divisions, long duct runs, added stops, or higher demand playing conditions.
Is CFM the same as wind pressure?
No. CFM measures airflow volume. Wind pressure measures force, often in inches of water. A blower must provide both enough airflow and enough pressure.
Why include leakage allowance?
Organs can leak through old leather, valves, conductors, chests, and joints. A leakage allowance helps prevent undersizing during real service conditions.
Why add reserve capacity?
Reserve capacity helps the organ handle strong passages without pressure sag. It also provides room for small future changes or measurement uncertainty.
Can this replace technician testing?
No. This is a planning calculator. Final blower selection should be checked with pressure readings, airflow measurements, noise review, and professional judgment.
What value should I use for airflow per pipe?
Use measured values when possible. For early planning, small flue pipes may need less, while large bass pipes and reeds may need more.
Why does altitude affect blower sizing?
Higher altitude reduces air density. The calculator increases corrected airflow demand to reflect thinner air at elevated locations.
What motor size should I choose?
Choose a practical motor rating above the suggested horsepower. Also consider duty cycle, noise, heat, vibration, control method, and installer guidance.