PU Tube FAQ — 15 Common Technical Questions by Automation Engineers
Q1. What are the two PU materials? How do Ester and Ether differ?
Ester handles wear; Ether handles moisture.
Ester offers excellent abrasion resistance and oil-mist tolerance, ideal for high movement or friction points. Ether has extremely low moisture absorption, staying stable in humid or wet-air environments.
Humidity or wet air → Ether
Dry, repeated bending → Ester
Q2. Do PU tubes absorb moisture? Will it shorten service life?
Ester absorbs moisture; Ether barely does.
Moisture triggers hydrolysis in Ester PU, gradually reducing flexibility and strength. Ether PU resists water absorption and maintains long-term performance.
Use Ether PU in any humid environment.
Q3. Can PU tubes burst because of moisture in pneumatic air?
No — moisture alone will not cause sudden failure.
The real risk is long-term hydrolysis in Ester PU. Once weakened, pressure spikes or vibration may cause rupture or pull-out from fittings.
Humid conditions → choose Ether PU.
Add shut-off fittings for extra safety.
Q4. What is the typical service life of PU tubing?
Service life depends heavily on environment.
Humidity, UV, temperature, and cycling stresses all influence PU aging. Ether lasts longer in humid environments; Ester excels in dry conditions with movement.
Treat PU tubing as a consumable. Inspect for whitening, haze, hardening, or cracks.
Q5. How do PU, Nylon 6 (PA6) and Nylon 12 (PA12) compare?
PU = most flexible; PA6 = stiffest; PA12 = strongest / highest pressure.
Each material solves a different engineering requirement.
Full comparison:
| Property | PU | PA6 | PA12 |
|---|---|---|---|
| Flexibility | ⭐⭐⭐⭐⭐ Softest | ⭐ Hardest | ⭐⭐ Medium |
| Pressure Rating | ⭐⭐⭐ | ⭐⭐⭐⭐ | ⭐⭐⭐⭐⭐ |
| Temperature Resistance | ~65°C | ~80°C | ~93°C |
| Moisture Absorption |
Ester: High Ether: Low |
High | Low |
| Bend Radius | Smallest | Largest | Medium |
| Typical Applications | Automation, dynamic motion | Dry, fixed lines | Main air lines / high pressure |
| Cost Level | Medium | Medium | Medium-High |
Tight bending → PU
Fixed routing → PA6
High pressure → PA12
Q6. Can PU be used in food-processing equipment?
Only food-grade Ether PU is acceptable.
Ether PU maintains stability in moisture. But food-contact uses require certified food-grade materials.
Ask SHPI for food-grade Ether PU.
Q7. Can PU tubes transport liquids?
Ester PU: air only. Ether PU: suitable for water; chemicals require testing.
Ester hydrolyzes in water. Ether PU is stable, but chemical compatibility varies widely.
Water → Ether PU
Oils / chemicals → request SHPI compatibility check
Q8. Which PU type is better for oil-mist environments?
Ester PU performs better.
Ester PU resists swelling and mechanical degradation from oil mist. Ether PU focuses on moisture resistance.
Oil-mist / lubricated air → Ester PU
Q9. How is working pressure determined for PU tubes?
PU typically uses a 1:3 ratio (Working Pressure : Burst Pressure).
Working pressure is affected by wall thickness, hardness, size, and temperature. Higher temperature reduces pressure capability.
Example:
| Specification | W.P. | B.P. |
|---|---|---|
| US805025M (8×5 mm PU Ester) | 15 bar | 45 bar |
Follow SHPI W.P. ratings; derate at higher temperatures.
Q10. Does tube hardness affect performance?
Yes — harder PU = higher pressure; softer PU = easier bending.
Harder PU increases stiffness and pressure rating but reduces flexibility. Softer PU improves routing at the cost of slightly lower pressure tolerance.
• High-pressure fixed lines → harder PU
• Tight bends / movement → softer PU
SHPI PU tubes are engineered with a balanced hardness window optimized for automation and pneumatic tools. This provides:
- Good abrasion resistance
- Easy installation and routing
- Stable pressure performance
- Excellent rebound and low deformation
This balanced hardness covers most factory pneumatic applications and is regarded as a stable, reliable choice.
Q11. Can PU tubes be used outdoors?
Ether PU is more suitable.
Ether PU maintains its properties better in humidity and changing outdoor conditions. Ester degrades faster from humidity and UV.
Outdoor → Ether PU (dark colors recommended for UV resistance)
Q12. Will PU tubes deform when over-bent?
Yes — bending below minimum radius causes deformation.
Over-bending flattens the tube, increases resistance, and introduces stress concentration leading to cracking or whitening.
Follow SHPI bend-radius guidelines to avoid premature failure.
Q13. What fittings are compatible with PU tubes?
PU tubes fit most pneumatic fittings.
PU elasticity seals well with push-in fittings, valves, and shut-off fittings.
For best installation feel → SHPI one-touch fittings
Q14. When should PU tubes be replaced?
Replace at the first sign of aging.
Whitening, cracks, hardening, or deformation indicate loss of mechanical strength and risk of failure.
Replace immediately when symptoms appear. Use batch tracking for maintenance.
Q15. How do I choose between Ester and Ether if I am unsure?
Humidity → Ether; Wear / oil-mist → Ester.
Ether solves moisture and hydrolysis issues; Ester offers superior abrasion and oil-mist resistance.
Share your operating conditions (humidity, pressure, temperature, bending, oil exposure) with SHPI for a precise recommendation.