High Temperature Roots Blower

A high temperature roots blower is designed for applications where inlet or discharge temperatures exceed standard limits – typically above 200°F discharge or 120°F ambient. High temperature service requires upgraded bearings (C4 clearance), stainless steel rotors (lower thermal expansion), synthetic lubricants (ISO VG 220), and often water cooling. Standard blowers fail rapidly in high temperature service.

Based on commissioning experience across glass plants, cement kilns, and industrial ovens, high temperature roots blowers require careful material selection and thermal management. Without proper upgrades, thermal expansion causes rotor contact, oil degradation, and bearing failure.

This guide covers high temperature requirements, component upgrades, cooling methods, and maintenance for elevated temperature service.

Table of Contents

• What Is a High Temperature Roots Blower?

• Temperature Limits

• Effects of High Temperature

• Component Upgrades

• Cooling Methods

• High Temperature Applications

• Selection Guide

• Performance and Engineering Calculations

• Installation Considerations

• Maintenance

• Frequently Asked Questions

• Final Thoughts

What Is a High Temperature Roots Blower?

A high temperature roots blower is a positive displacement rotary lobe machine designed for elevated temperature service – inlet temperatures above 120°F or discharge temperatures above 200°F. Standard blowers are designed for ambient air at 60–100°F. High temperature service demands upgraded components.

High temperature features:

• C4 bearings (increased clearance for thermal expansion)

• Stainless steel rotors (lower thermal expansion)

• Synthetic lubricant (ISO VG 220 – higher viscosity)

• Water cooling (heads and/or oil cooler)

• High-temperature seals

• Temperature monitoring

Based on field data, standard blowers operated above 200°F discharge experience bearing failure in 15,000–20,000 hours – half normal lifespan. High temperature upgrades restore normal life.

Temperature Limits

Standard blower limits:

• Discharge temperature: 200°F continuous (250°F peak)

• Ambient temperature: 104°F (40°C)

• Oil temperature: 200°F (oil degradation above)

High temperature blower limits:

• Discharge temperature: 250°F continuous (with upgrades)

• Ambient temperature: 120°F+ (with cooling)

• Oil temperature: 230°F (synthetic oil)

Effect of temperature on components:

Effects of High Temperature

On rotors:

• Thermal expansion reduces tip clearance

• Cast iron: expansion 0.000011 in/in/°F

• Stainless steel: expansion 0.0000096 in/in/°F

• At 250°F, clearance reduction: 0.10–0.15 mm

• Risk of rotor contact if clearance too tight

On bearings:

• Bearing life halves for every 25°F above 200°F

• At 220°F: 50% of normal life

• At 240°F: 25% of normal life

• C4 bearings accommodate thermal expansion

On oil:

• Oil life halves for every 18°F above 200°F

• At 220°F: 50% of normal life

• At 240°F: 25% of normal life

• Synthetic oil handles higher temperatures

On seals:

• Lip seals harden at high temperature

• Labyrinth seals better for high temperature

• Seal leakage increases

On casing:

• Thermal expansion changes clearances

• Casing expands less than rotors (cooler)

• Differential expansion reduces clearance

Component Upgrades

Rotors (impeller).

• Standard: cast iron – higher thermal expansion

• Upgrade: stainless steel (410, 416, 316L) – lower expansion

• Stainless expands 12% less than cast iron

• Reduces clearance closure risk

Bearings.

• Standard: C3 clearance

• Upgrade: C4 clearance (increased clearance)

• C4 accommodates thermal expansion

• Prevents bearing seizure

• Brand: SKF, FAG, NSK (C4 grade)

Lubricant.

• Standard: ISO VG 150 synthetic

• Upgrade: ISO VG 220 synthetic

• Higher viscosity for high temperature

• Better film strength at elevated temperature

Seals.

• Standard: lip seals

• Upgrade: high-temperature lip seals or labyrinth

• Labyrinth seals better at high temperature

• No contact – less wear

Cooling.

• Standard: air cooling

• Upgrade: water cooling (heads and/or oil cooler)

• Water cooling reduces discharge temperature 20–40°F

• Oil cooler extends oil life

Casing.

• Standard: ductile iron

• Upgrade: thicker casing for high temperature

• Higher safety factor

• Stainless steel for corrosive hot gas

Cooling Methods

1. Air cooling (standard).

• Adequate up to 200°F discharge

• Requires cool inlet air

• Duct outside air – not recirculated

2. Water-cooled heads.

• Water jacket around cylinder heads

• Reduces discharge temperature 20–40°F

• Required above 18 psig continuous

• Water flow: 2–10 gpm depending on size

3. External oil cooler.

• Cools oil after gearbox

• Extends oil life

• Reduces bearing temperature

• Required above 220°F discharge

4. Intercooling (staged compression).

• Cooling between stages

• For high-pressure high-temperature

• Complex – only for special applications

5. Inlet air cooling.

• Cool inlet air (ambient)

• Duct from cooler location

• Reduces discharge temperature

High Temperature Applications

Glass industry. Combustion air for glass furnaces. Ambient 120°F+. Discharge 200–240°F. C4 bearings, stainless rotors, water cooling.

Cement plants. Hot ambient (120°F+). Pneumatic conveying. Discharge 210–250°F. C4 bearings, ISO VG 220 oil, water cooling above 12 psig.

Steel plants. Hot ambient (120°F+). Combustion air. Discharge 210–250°F. C4 bearings, stainless rotors, water cooling.

Industrial ovens. Process air for drying, curing. Inlet air 100–150°F. Discharge 220–260°F. High temperature design.

Power plants. Combustion air. Hot ambient. Ash handling (hot). C4 bearings, water cooling.

Chemical plants. Hot gases. High temperature service. Stainless steel. Water cooling.

Biogas (high temperature). Hot gas from digesters. Stainless steel. Temperature monitoring.

Selection Guide

Step 1 – Define temperatures.

• Inlet temperature (°F)

• Ambient temperature (°F)

• Discharge temperature (°F)

• Maximum temperature

Step 2 – Determine if high temperature design is needed.

• Discharge >200°F: high temperature upgrades recommended

• Discharge >220°F: high temperature design required

• Ambient >104°F: high temperature design required

Step 3 – Select rotor material.

• Cast iron: for discharge <200°F

• Stainless steel: for discharge >200°F (lower thermal expansion)

Step 4 – Select bearings.

• C3: for standard temperature

• C4: for discharge >200°F (accommodates thermal expansion)

Step 5 – Select lubricant.

• ISO VG 150: standard

• ISO VG 220: for discharge >200°F

Step 6 – Specify cooling.

• Air cooling: discharge <200°F

• Water cooling: discharge >220°F continuous

Step 7 – Specify temperature monitoring.

• Thermocouple at discharge

• Alarm and shutdown

Performance and Engineering Calculations

Thermal expansion calculation:
ΔL = L × α × ΔT

For 200 mm rotor, temperature rise 180°F:

• Cast iron: ΔL = 200 × 0.000011 × 180 = 0.40 mm

• Stainless: ΔL = 200 × 0.0000096 × 180 = 0.35 mm

• Difference: 0.05 mm (stainless expands less)

Clearance reduction:

• Casing expands less than rotors (cooler)

• Net clearance reduction: 0.10–0.25 mm

• Cold clearance must allow for expansion

High temperature clearance:

• Cold clearance: 0.10–0.15 mm (standard)

• For high temperature: 0.15–0.20 mm cold

• Hot clearance: should not close to zero

Discharge temperature calculation:
Tdischarge = Tinlet × (Pdischarge/Pinlet)^0.286 + ΔTmechanical

At 8 psig, 80°F inlet: 153°F theoretical + 30–50°F mechanical = 185–200°F
At 15 psig, 80°F inlet: 175°F theoretical + 40–60°F mechanical = 215–235°F

Installation Considerations

Blower location.

• Locate in cooler area if possible

• Avoid heat sources

• Provide cooling air – duct from outside

Inlet air.

• Duct from coolest location

• Do not recirculate hot air

• Every 10°F inlet reduction = 10°F discharge reduction

Cooling water.

• Water-cooled heads: 2–10 gpm depending on size

• Oil cooler: 2–5 gpm

• Water temperature: <90°F

• Water quality: clean, treated

Piping.

• Allow for thermal expansion

• Flexible connectors

• Support piping

Monitoring.

• Thermocouple at discharge

• Bearing temperature sensors

• Pressure gauges

Maintenance

High temperature maintenance:

• Change oil more frequently (heat degrades oil)

• Check bearing temperature daily

• Monitor discharge temperature

• Inspect seals for hardening

Oil change intervals (high temperature):

• Standard: 5,000–6,000 hours

• High temperature (>220°F): 2,500–3,000 hours

• Use ISO VG 220 synthetic

Bearing replacement:

• High temperature reduces bearing life

• Monitor vibration and temperature

• Replace at 25,000–30,000 hours (vs 40,000–50,000 standard)

Clearance check:

• Measure clearance hot and cold

• Cold clearance should allow for expansion

• Replace rotors if hot clearance closes to zero

Frequently Asked Questions

1. What is the maximum temperature for a roots blower?
Standard: 200°F discharge continuous. High temperature design: 250°F discharge continuous with upgrades (C4 bearings, stainless rotors, water cooling). Above 250°F, discharge temperature and thermal expansion become critical.

2. What upgrades are needed for high temperature?
C4 bearings (increased clearance for thermal expansion), stainless steel rotors (lower thermal expansion), synthetic ISO VG 220 oil (higher viscosity), water cooling (heads and/or oil cooler), high-temperature seals, and temperature monitoring.

3. How does temperature affect tip clearance?
Thermal expansion reduces tip clearance. At 250°F, clearance reduction is 0.10–0.15 mm. Cold clearance must be increased to compensate. Stainless steel rotors expand less than cast iron – preferred for high temperature.

4. What oil should I use for high temperature?
Use ISO VG 220 synthetic oil – higher viscosity for high temperature. Standard ISO VG 150 degrades faster above 200°F. Change oil more frequently – 2,500–3,000 hours vs 5,000–6,000 hours.

5. What bearings are used for high temperature?
C4 bearings (increased clearance) for high temperature applications. Standard C3 bearings fail from thermal expansion. C4 bearings accommodate expansion – preventing seizure.

6. When is water cooling required?
Water cooling is recommended for continuous duty above 18 psig or discharge temperatures above 220°F. Water-cooled heads reduce discharge temperature 20–40°F. Oil cooler extends oil life.

7. How does high temperature affect bearing life?
Bearing life halves for every 25°F above 200°F. At 220°F: 50% of normal life. At 240°F: 25% of normal life. High temperature bearings (C4) and water cooling extend life.

8. Can I use a standard blower for high temperature?
For intermittent service up to 220°F, maybe. For continuous service above 200°F, standard blowers will fail prematurely – bearings, oil, and rotors are not designed for high temperature. Specify high temperature design for continuous service.

9. What is the difference between C3 and C4 bearings?
C3 is standard clearance for most applications. C4 is increased clearance for high-temperature applications. C4 accommodates thermal expansion of shaft and housing. Using C3 in high temperature causes bearing seizure.

10. How do I monitor high temperature operation?
Install thermocouple at discharge with alarm and shutdown (set at 250°F). Bearing temperature sensors with alarm at 210°F. Record temperatures daily.

11. What is the effect of altitude on high temperature?
Altitude reduces cooling effectiveness – both air cooling and motor cooling. At 5,000 ft, air cooling is 17% less effective. Derate blower or add water cooling.

12. Can high temperature blowers handle hot gas?
Yes – with stainless steel construction. For corrosive hot gas, specify 316L stainless rotors and casing. For high temperature (250°F+), specify special materials.

13. What is the payback for high temperature upgrades?
High temperature upgrades add 30–50% to blower cost. Without upgrades, blower fails in 15,000–20,000 hours. With upgrades, normal life (40,000–50,000 hours). Payback: 1–2 years through avoided replacement.

14. How do I size a high temperature blower?
Correct flow for temperature: ACFM = SCFM × (T/520). Higher temperature = more volume. Correct pressure ratio for temperature. Consult manufacturer for high temperature performance curves.

15. What is the maximum ambient temperature?
Standard: 104°F (40°C). High temperature design: 120°F+ with cooling. Above 120°F, water cooling recommended. Motor derating also required at high ambient.

Final Thoughts

After commissioning high temperature roots blowers, here is my practical advice:

Selection logic. For discharge temperatures above 200°F, specify C4 bearings, stainless steel rotors, ISO VG 220 oil, and temperature monitoring. For continuous duty above 220°F, add water cooling. Zhanggu and other manufacturers offer high temperature configurations.

Thermal expansion is the main threat. Rotors expand more than casing. Without proper cold clearance, rotors contact at operating temperature. Stainless steel rotors expand less – preferred for high temperature.

Oil is the weak link. Heat degrades oil. Change oil more frequently. Use ISO VG 220 synthetic. Monitor oil condition. Oil failure causes bearing failure.

The economic reality. High temperature blowers cost 30–50% more than standard blowers. But standard blowers fail in 15,000–20,000 hours in high temperature service. High temperature blowers last 40,000–50,000 hours. The payback is 1–2 years. Specify correctly – the upgrades pay for themselves.