Pneumatic conveying blower packages

What does a conveying blower package include?

Dilute-phase pneumatic conveying of cement, fly ash, flour, sugar, plastic granules, grain and many chemical powders is driven by low-pressure blowers. A complete package usually includes:

• The blower: Roots (lobe), screw or, for larger and steadier duties, centrifugal.
• Motor, belt or direct drive, base frame and acoustic enclosure.
• Inlet filter and inlet silencer.
• Discharge silencer, pressure relief valve, non-return valve and start-unload or blow-off valve.
• Pressure and temperature gauges or transmitters, and often a flow meter.
• Controls: starter or variable-frequency drive (VFD), interlocks with the rotary valve or blow tank, and alarms.
• For pressure systems, an aftercooler where the product is heat-sensitive; for vacuum systems, a filter and protective vacuum relief.

Dense-phase conveying, which uses blow tanks at higher pressures, is normally fed by compressors rather than blowers; see our page on dense-phase air supply.

Who decides what: the conveying designer and the blower side

A conveying system works only if two responsibilities meet cleanly:

• The conveying designer sets the material properties, conveying mode, solids throughput, pipe route and diameter, minimum pick-up velocity, solids loading and the line pressure drop with product.
• The blower package must supply the required actual air volume and differential pressure for minimum, normal, peak, start-up and upset cases, within the blower’s temperature, speed and pressure limits.

When the boundary is unclear, each side assumes the other has added margin, and the system either blocks or wastes energy. Write the duty down as numbers that both sides sign off.

Why systems fail despite adequate nameplate flow

Conveying blowers fail in service for a short list of reasons:

1. Reference flow mistaken for delivered flow. Catalogue capacity is at a reference inlet condition. Hot inlet air, a choked filter, belt slip and internal leakage at higher differential all reduce what reaches the pick-up point.
2. Air-only pressure drop used instead of loaded pressure drop. With product in the line, pressure drop rises sharply because of solids acceleration, friction, bends, diverters and the receiving filter.
3. Velocity checked at the wrong point. Air expands along the line as pressure falls, so velocity is lowest at the pick-up end of a pressure system. That is where the minimum conveying velocity must be met.
4. Turndown without checking conveying stability. Reducing airflow to save power can drop velocity below the safe limit, causing deposition, slugging and blockages.
5. Relief valve set too close to working pressure. A small rise in loading lifts the relief valve, flow drops and the line blocks.

Sizing the airflow: velocity at the pick-up point

The blower is sized so that air velocity at the pick-up point stays above the material’s minimum conveying velocity, with margin. For a pressure system, the actual volume at the pick-up point is the free-air volume corrected to the local pressure and temperature:

Q_pick-up = Q_{free air} × (P_atm / P_pick-up) × (T_pick-up / T_inlet)

with absolute pressures and kelvin temperatures. Velocity is Q_pick-up divided by the pipe cross-section.

Worked example: a 100 mm bore line (area about 0.00785 m²) conveying at 0.8 bar gauge at the pick-up point (1.81 bar a). If the designer requires a velocity of about 20 m/s there, the actual volume at pick-up is 20 × 0.00785 × 3,600 ≈ 565 m³/h. Converting back to free air at the blower inlet (ignoring temperature for this screening) gives 565 × 1.81 / 1.013 ≈ 1,010 m³/h free air. Add allowances for blower slip at that differential, rotary-valve leakage and inlet temperature, and the blower must deliver noticeably more than 1,010 m³/h. Minimum velocities differ widely between materials; they come from the conveying designer or material testing, not from a generic table.

Use our pneumatic conveying enquiry calculator to organise these figures before you ask for a quotation.

Which blower type for which conveying duty?

The near-constant flow of a positive-displacement blower is why Roots and screw machines dominate conveying. As the line loads up, the blower pushes harder instead of backing off, which helps clear the line, up to its relief setting.

Pressure, temperature and protection

• Relief valve: set below the blower’s maximum allowable differential but with clear headroom above the highest normal conveying pressure.
• Discharge temperature: a Roots blower’s discharge can be well above 100 °C at higher differentials, more in summer. Heat-sensitive products (sugar, some polymers, food powders) may need an aftercooler.
• Air quality: oil-free blowers keep oil out of the air, but timing-gear and bearing seals must be in good order; food and pharma products may also need inlet filtration and moisture control.
• Interlocks: the rotary valve or feeder should stop on blower trip or high line pressure, and the blower should keep running to purge the line before shutdown.
• Shutdowns and alarms: high discharge temperature, high differential pressure, motor overload and, on larger machines, vibration.

Noise, pulsation and installation

Positive-displacement blowers generate strong pressure pulsations and noise. Inlet and discharge silencers, an acoustic enclosure and flexible connectors are normal parts of a package. Installation checks that matter in Indian plants:

• Clean, cool inlet air; cement, fly-ash and flour plants are dusty, so inlet filters need regular inspection.
• Ventilation of the blower room or enclosure for summer temperatures of 40–45 °C, and above 45 °C on open sites.
• Pipe supports so that the blower does not carry the conveying-line weight or thermal growth.
• Access for belt changes, oil changes and filter elements.
• Earthing and static control for combustible dusts, as decided by the plant’s safety engineers.

Standby and commissioning

If conveying stops, production stops. Plants with one conveying line often keep a standby blower that can be valved in quickly; plants with several lines may share a standby through a manifold. Rental blowers or compressors can cover planned overhauls.

A loaded commissioning test proves the package:

1. Run air only and record inlet conditions, line pressure and blower data as a baseline.
2. Introduce product in steps to the design throughput; record line pressure, blower current and discharge temperature.
3. Check pick-up velocity at the highest loading against the designer’s minimum.
4. Test the interlocks: feeder trip on blower failure, high-pressure alarm and purge before shutdown.
5. Run at the hottest time of day if possible, or correct the results for summer inlet temperature.
6. Keep the records as the baseline for future troubleshooting.

Common problems and first checks

How Reddy Compressors helps

We sell new and used or refurbished blowers (Roots, screw, centrifugal and side-channel), rent them, service them and supply their spares, alongside compressors for dense-phase systems. We are an independent multi-brand specialist at Tarnaka, Secunderabad, serving industry since 2002, and not an authorised dealer of any brand. We have tie-ups with all major and reputed brands.

• We check your conveying duty figures, convert them to actual site conditions and confirm whether an existing blower can meet them.
• We supply complete blower packages with silencers, relief and non-return valves, filters, enclosures and VFDs where they help.
• We service and overhaul conveying blowers: bearings, timing gears, seals, rotors, belts and oil, with before-and-after readings.
• We supply temporary blowers or compressors to cover overhauls and breakdowns.
• We identify spares from the nameplate and old part and confirm fit before quoting.

Our service teams, with over 20 service engineers and technicians, cover Telangana and Andhra Pradesh, and we supply equipment and spares across India. The conveying design itself (material velocities and loading) stays with your conveying designer.

What to send us

• Material, throughput (tonnes per hour) and conveying mode (dilute or dense, pressure or vacuum).
• Line diameter, length, number of bends and vertical lift.
• Designer’s required air volume and pressure, or the minimum pick-up velocity.
• Existing blower nameplate photos, motor rating and running pressure.
• Site ambient conditions and any product temperature limits.
• The problem you are seeing: blockages, low throughput, heat or noise.

Frequently asked questions

How do I size a blower for pneumatic conveying?

Start from the conveying design: the minimum air velocity the material needs at the pick-up point, the pipe size and the loaded line pressure drop. Convert the required velocity to actual volume at pick-up pressure, then back to free air at the blower inlet. Add allowances for blower slip, rotary-valve leakage and hot inlet air, and check the blower at that flow and differential pressure.

Why does my pneumatic conveying line keep blocking?

The usual cause is air velocity falling below the material’s minimum at the pick-up point. That happens when the feeder over-feeds, the relief valve lifts, belts slip, the inlet filter chokes or the blower has worn. Check line pressure against the design figure, the relief setting, blower speed and delivered flow. Rotary-valve leakage can also steal air from the line.

Roots blower or screw blower for pneumatic conveying?

Roots blowers suit most dilute-phase systems up to about 1 bar gauge; they are simple, robust and easy to service. Screw blowers cost more but use less power at higher pressures and suit larger continuous systems up to about 2–3.5 bar gauge. Compare them at your duty point and inlet temperature, and include spares and service availability in the decision.

What pressure does a dilute-phase conveying blower need?

It depends on the material, distance, bends, throughput and pipe size. Many dilute-phase pressure systems run somewhere between about 0.3 and 1 bar gauge (about 4–15 psig), with longer or heavier systems higher. The conveying designer calculates the loaded pressure drop; the blower and relief valve are then selected with headroom above it.

Do I need an aftercooler on a conveying blower?

Only if the product or the line needs it. A Roots blower’s discharge air can be well above 100 °C at higher pressures, especially in an Indian summer. Heat-sensitive materials such as sugar, some food powders and some plastics can soften, cake or degrade. An aftercooler brings the air close to ambient, though condensation must then be drained.

Can you rent a blower while ours is being overhauled?

Yes. We rent blowers and compressors and can provide temporary units to cover planned overhauls or breakdowns, matched to your flow and pressure. Send the existing nameplate details, the running pressure and the connection sizes so the temporary unit fits your line and controls. We also service and overhaul the blower itself.

Related pages

• Dilute phase conveying air supply
• Dense phase conveying air supply
• Pneumatic conveying system requirements
• Roots blowers
• Positive displacement blower pulsation and silencing
• Cement plant compressed air engineering