Manufacturing
Rotary screw air compressor
Compressed air is the most expensive utility in the plant. The physics shows where it goes.
An air compressor turns electricity into pressure. How much power it takes for the same air is set by the pressure ratio, the filters and the leaks. We read all three from the meter.
300 acfm at 125 psig, 75 hp
- Full-load input
- 54.1 kW
- Specific power
- 18.0 kW per 100 cfm
- Delivery
- 300 acfm
- Setpoint
- 125 psig
Anatomy and nameplate
- 1Inlet filter pressure drop. Restriction raises the pressure ratio.
- 2Airend discharge temperature and pressure. Shows cooler fouling and separator loading.
- 3Separator pressure drop. The element clogs. Power climbs for the same air.
- 4Oil temperature. Oil flow and cooler health.
- 5Motor current. Package power without a new meter.
- 6Airend vibration. Rotor and bearing condition.
- 7Line pressure. Setpoint and the demand it has to hold.
- 8Power meter. The number the baseline is measured against.
| Performance | |
|---|---|
| Type | Oil-flooded rotary screw, single stage |
| Free air delivery | 300 acfm |
| Rated pressure | 125 psig |
| Full-load input power | 54.1 kW |
| Specific power | 18.0 kW per 100 cfm |
| Rotor profile | 4 male lobes, 6 female lobes |
| Male rotor speed | 3,560 rpm |
| Discharge temperature | 185–195 °F |
| Motor and package | |
| Motor | 75 hp (55 kW), 4-pole, TEFC |
| Supply | 460 V, 3-phase, 60 Hz |
| Full-load current | 84 A |
| Separator pressure drop | 3 psi new, change at 10 psi |
| Cooling | Air-cooled oil and air coolers, 1.5 kW fan |
| Oil charge | 12 gal synthetic |
The physics
The equations behind every curve on this page.
Compression work
P = k/(k−1)·p1·Q1·[(p2/p1)^((k−1)/k) − 1] / η
More pressure ratio, more power, for every cubic foot.
Specific power
kW per 100 cfm
18.0 kW per 100 cfm at full load and 125 psig.
Orifice leak
ṁ = Cd·A·p0·√(k/(R·T0))·(2/(k+1))^((k+1)/(2(k−1)))
Flow through a hole grows with the square of its diameter.
What the air costs
Power follows the pressure ratio. The separator sits in the path, so a clogging element adds to it.
Input power against system pressure
300 acfm delivered, new separator element
- Input power at 300 acfm
- Each +2 psig
- +0.8% power
Every extra pound of pressure is paid for in power on every cubic foot. The rule of thumb that 2 psi costs about 1% falls out of the equation.
P = k/(k−1) · p1 · Q1 · [(p2/p1)^((k−1)/k) − 1] / η
Clogging separator: more power for the same air
- Input power at 300 acfm and 125 psig
- Cost of waiting
- 3.1 kW, about $2,069 a year
The airend has to push against the separator as well as the plant. Output stays the same, the meter climbs.
p_airend = p_line + Δp_separator + Δp_piping
Leaks
Leaks are free air that someone paid to compress. The size of the hole sets the size of the bill.
What a leak costs
- Air lost at 125 psig
- Power wasted (right axis)
Flow through a small hole grows with the square of its diameter. A few small leaks can eat the output of a whole compressor.
ṁ = Cd·A·p0·√(k/(R·T0))·(2/(k+1))^((k+1)/(2(k−1)))
Failure modes
What breaks, what it looks like, what the twin does about it.
| Failure mode | The physics | Signals that show it | How the twin catches it |
|---|---|---|---|
| Separator element clogging | Pressure drop across the element adds to the airend discharge pressure. | Separator differential pressure up. Package kW up at the same flow. | Expected kW at the current pressure and flow. The gap is the clogging. |
| Air leaks | Choked flow through holes in pipes, couplings and tools. | Unloaded-time falls. Idle kW rises. Pressure sags at night. | Converts off-shift flow into equivalent hole size and kW. |
| Cooler fouling | Less heat leaves the oil, so discharge temperature rises. | Discharge temperature up at the same ambient. | Heat balance on the oil circuit. Compares expected and measured temperature. |
| Airend bearing wear | Rotor bearing defects ring at fixed geometric frequencies. | Vibration lines at bearing frequencies. Rising motor current. | Tracks band energy at the predicted frequencies. |
| Inlet filter loading | Low inlet pressure raises the pressure ratio. | Inlet vacuum. Falling delivered flow. | Flags the added kW and the day the filter pays for itself. |
How we catch it early
A physics twin and a PINN, working on one rotary screw air compressor.
The twin is a set of equations for this machine, tuned to its nameplate. Give it the flow, speed and conditions and it returns what every reading should be. It always gives the same answer for the same inputs.
A physics-informed neural network, or PINN, sits on top. It is trained on the plant’s own data and it is penalized whenever it breaks a physics rule. So it can only learn what the equations leave out: wear, fouling, friction. It cannot invent an answer that the machine could never produce.
Step 1
Measure
Flow, pressure, current, temperature, vibration. Whatever the asset already has.
Step 2
Physics twin
The equations of this machine, set to its nameplate. It says what the readings should be right now.
Step 3
Residual
Measured minus expected. Demand, weather and speed are already taken out.
Step 4
PINN
A small neural network that learns the cause of the gap, under the physics rules.
Step 5
Finding
A named cause, a date, and the kWh or hours at stake. An engineer reviews it.
loss = (measured − predicted)² + λ · (physics residual)²
The second term is the rulebook. It is zero when the network obeys the equations.
Why this beats black-box AI
A black-box model learns patterns from history. It needs examples of each failure, and it goes quiet when the pump runs at a point it has not seen. The twin starts from physics, so it works on day one. The PINN adds what physics cannot know about this particular machine.
That is also what makes the savings countable. The baseline is a calculation, not a guess, so the gap between baseline and meter is a number a customer can check.
What the twin checks on this asset
- Specific power: 18.0 kW per 100 cfm
- Separator pressure drop against the 10 psi change point
- Off-shift flow converted to leak size
- Discharge temperature against the heat balance
| Fixed alarm | Black-box AI | Twin + PINN | |
|---|---|---|---|
| Needs failure history to learn | No | Yes, lots | No |
| Says what is wrong | No | Rarely | Yes, by name |
| Works at a flow it has never seen | No | Often fails | Yes, the equations still hold |
| Puts a number on the saving | No | No | Yes, in kWh and dollars |
| Lead time on slow wear | Late | Varies | Weeks to months |
| Every number can be traced | Yes | No | Yes, to an equation |
What the twin puts a number on
Energy and cost, from the equations.
Full-load input power
54.1 kW
300 acfm at 125 psig
Clogged separator, 18 psi
3.1 kW
$2,069 a year at 6,000 hours
One 1/8 in leak
3.7 kW
20 scfm lost
Pressure setpoint
0.8% per 2 psig
Lower the setpoint where the process allows
What we do for you
We watch it. We catch it. We prove it.
Our reliability engineers run the twin on your rotary screw air compressor, review every finding, and help your crew fix it. After the repair we compare the meter to the baseline and write the result in the ledger.