Hose and Tubing Selection for Fluid Systems

Understanding the Fundamentals of Hose and Tubing Selection

Selecting the appropriate hose and tubing for fluid systems represents one of the most critical decisions in mechanical engineering design. Whether you're developing hydraulic systems for Maritime fishing vessels, pneumatic controls for manufacturing facilities in Nova Scotia, or process piping for industrial applications across Atlantic Canada, the consequences of improper selection can range from minor inefficiencies to catastrophic failures.

The selection process requires careful consideration of multiple interconnected factors, including operating pressure, temperature ranges, chemical compatibility, flexibility requirements, and environmental conditions. In our region's demanding climate—where temperatures can swing from -30°C in winter to +35°C in summer—these considerations become even more pronounced.

At its core, the distinction between hoses and tubing lies in their construction and intended application. Tubing typically refers to rigid or semi-rigid conduits measured by their outside diameter (OD), while hoses are flexible assemblies often reinforced with textile braiding, wire spirals, or composite materials. Understanding when to specify each type forms the foundation of effective fluid system design.

Key Selection Criteria for Fluid System Applications

Pressure Ratings and Safety Factors

The working pressure of your fluid system dictates the minimum wall thickness and reinforcement requirements for any hose or tubing selection. Industry standards typically recommend a 4:1 safety factor for static applications, meaning a hose rated for 400 bar (5,800 psi) working pressure should have a minimum burst pressure of 1,600 bar (23,200 psi).

For dynamic applications involving pressure cycling, impulse testing becomes essential. SAE J517 standards specify impulse test requirements ranging from 150,000 to 1,000,000 cycles depending on the hose classification. Applications common in Atlantic Canada's resource extraction and marine industries often experience significant pressure fluctuations, making impulse resistance a critical selection parameter.

• Low-pressure applications (0-20 bar): Unreinforced tubing, single-braid hoses

• Medium-pressure applications (20-100 bar): Single or double steel-braid reinforcement

• High-pressure applications (100-400 bar): Multiple spiral-wire reinforcement

• Ultra-high-pressure applications (400+ bar): Specialty constructions with four or six spiral layers

Temperature Considerations

Temperature affects both the fluid being conveyed and the hose or tubing material itself. Most elastomeric hose materials experience significant property changes at temperature extremes. Standard nitrile (NBR) rubber inner tubes perform well between -40°C and +100°C, while EPDM compounds extend the lower range to -50°C but offer limited petroleum resistance.

For Nova Scotia's industrial applications, where outdoor equipment may sit idle during harsh winters before operating at elevated temperatures, the temperature cycling effect on material fatigue deserves careful attention. PTFE-lined hoses offer exceptional temperature range (-70°C to +260°C) but at significantly higher cost and with reduced flexibility.

Chemical Compatibility

The inner tube or liner material must resist degradation from the conveyed fluid, while the outer cover must withstand environmental exposure. Common compatibility requirements include:

• Petroleum-based hydraulic fluids: Nitrile (NBR), hydrogenated nitrile (HNBR)

• Synthetic hydraulic fluids: Viton (FKM), EPDM (for phosphate esters)

• Water and water-glycol: EPDM, chloroprene (Neoprene)

• Acids and caustics: PTFE, UHMWPE liners

• Food-grade applications: Silicone, PTFE, FDA-approved compounds

Maritime industries in Atlantic Canada frequently encounter saltwater exposure, requiring outer covers with enhanced resistance to chloride-induced degradation. Chloroprene and EPDM compounds generally outperform standard nitrile in these environments.

Material Options and Their Applications

Rubber and Elastomeric Hoses

Rubber hoses remain the workhorse of industrial fluid transfer, offering an excellent balance of flexibility, pressure capability, and cost-effectiveness. Modern rubber hose construction typically features a three-layer design: an inner tube for fluid compatibility, reinforcement layers for pressure containment, and an outer cover for environmental protection.

The reinforcement configuration significantly impacts performance characteristics. Braided reinforcement using high-tensile steel wire provides excellent flexibility and is preferred for applications requiring tight bend radii. Spiral reinforcement offers superior impulse resistance and higher pressure ratings but with reduced flexibility and larger minimum bend radii—typically 1.5 to 2 times the hose OD compared to 0.75 to 1 times for braided constructions.

Thermoplastic Hoses

Thermoplastic hoses, constructed from materials such as nylon, polyester, or polyurethane, offer distinct advantages for specific applications. Their non-conductive properties make them suitable for paint spray systems and applications requiring electrical isolation. Thermoplastic constructions typically weigh 30-50% less than equivalent rubber hoses while offering superior abrasion resistance.

However, thermoplastic hoses generally exhibit reduced flexibility at low temperatures—a significant consideration for outdoor applications in Nova Scotia's climate. Most thermoplastic compounds become noticeably stiffer below -20°C, potentially affecting system performance during winter operations.

Metal Tubing and Hose

For the most demanding applications, metal tubing and corrugated metal hose assemblies provide unmatched durability and temperature resistance. Stainless steel tubing (commonly 304 or 316 grade) handles temperatures from cryogenic to +800°C while offering excellent chemical resistance.

Corrugated metal hoses combine the durability of metal construction with the flexibility required for vibration isolation and thermal expansion compensation. These assemblies are common in Maritime industrial facilities handling steam, exhaust gases, or aggressive chemicals.

Composite and Specialty Constructions

Modern composite hoses feature multiple layers of different materials, each optimised for specific functions. A typical composite construction might include:

• Inner wire helix for vacuum resistance and anti-collapse properties

• Multiple polymer film layers for chemical barrier protection

• Fabric reinforcement for pressure containment

• External wire helix for kink resistance and external pressure protection

• Polypropylene or polyester outer cover for abrasion and weather resistance

These constructions excel in chemical transfer applications where no single material provides adequate resistance to all conveyed products—common in Atlantic Canada's petroleum terminals and chemical processing facilities.

Sizing Calculations and Flow Considerations

Proper sizing ensures adequate flow capacity while minimising energy losses and preventing damage from excessive fluid velocity. The fundamental relationship between flow rate, velocity, and cross-sectional area governs all sizing decisions:

Q = A × V

Where Q represents volumetric flow rate, A represents the internal cross-sectional area, and V represents fluid velocity.

For hydraulic systems, recommended fluid velocities typically fall within the following ranges:

• Suction lines: 0.6-1.2 m/s (to prevent cavitation)

• Return lines: 2-4 m/s

• Pressure lines: 4-6 m/s (standard), up to 8 m/s (high-pressure systems)

Exceeding these velocities generates excessive pressure drop, increases fluid temperature through friction heating, and accelerates erosion of hose inner tubes—particularly problematic in systems handling fluids with suspended particles.

Pressure drop calculations become critical for longer hose runs common in large industrial facilities and mobile equipment. The Darcy-Weisbach equation provides accurate predictions when combined with appropriate friction factors for the specific hose construction. As a rule of thumb, pressure drop should not exceed 5% of system working pressure under normal operating conditions.

Installation Best Practices and Common Pitfalls

Bend Radius and Routing

Every hose has a specified minimum bend radius—the tightest curve the hose can follow without experiencing internal damage or flow restriction. Violating minimum bend radius requirements represents one of the most common causes of premature hose failure.

Critical routing guidelines include:

• Maintain at least two hose diameters of straight length before any fitting

• Avoid twist during installation—even 7° of twist can reduce service life by 90%

• Allow for hose length changes (up to ±4% with pressure cycling)

• Protect hoses from external abrasion using guards, sleeves, or clamps

• Support long horizontal runs to prevent sagging and stress concentration

Fitting Selection and Assembly

The hose-fitting interface represents the most failure-prone location in any hose assembly. Reusable fittings offer field serviceability but require careful assembly and periodic inspection. Permanent crimped fittings provide superior reliability when properly assembled using calibrated crimping equipment.

Crimp specifications vary significantly between hose types and fitting manufacturers. A typical hydraulic hose might require crimp diameters accurate to ±0.1 mm—tolerances achievable only with properly maintained equipment and trained personnel. Under-crimping results in hose blowoff under pressure, while over-crimping damages the inner tube and causes premature failure.

Environmental Protection

Atlantic Canada's harsh environment demands particular attention to environmental protection. Salt spray, UV exposure, ozone, and temperature extremes all attack hose materials. Effective protection strategies include:

• UV-resistant outer covers or protective sleeves for exposed installations

• Fire-resistant sleeves near heat sources or in regulated environments

• Abrasion-resistant spiral wraps for mobile equipment applications

• Corrosion-resistant fittings (zinc-nickel plating or stainless steel) for marine applications

Maintenance, Inspection, and Replacement Criteria

Even properly selected and installed hoses have finite service lives. Establishing systematic inspection and replacement programmes prevents unexpected failures and the safety hazards they create.

Visual inspection should occur at regular intervals—monthly for high-pressure hydraulic systems, quarterly for lower-risk applications. Key indicators requiring immediate attention include:

• Cover damage exposing reinforcement layers

• Blistering, cracking, or softening of cover material

• Kinking, flattening, or permanent deformation

• Fitting corrosion, movement, or leakage

• Reinforcement wire exposure or breakage

Many facilities in Nova Scotia's industrial sector have adopted time-based replacement programmes, replacing critical hoses at fixed intervals regardless of apparent condition. High-pressure hydraulic hoses in demanding applications often warrant replacement every 3-5 years, while lower-pressure applications may permit 7-10 year service life.

Documentation of all hose assemblies—including installation date, specifications, and inspection history—enables data-driven replacement decisions and supports regulatory compliance for applicable industries.

Industry Standards and Regulatory Considerations

Multiple standards organisations govern hose and tubing specifications, with selection depending on application type and regulatory jurisdiction:

• SAE International: J517 (hydraulic hose), J1402 (air brake hose)

• ISO Standards: ISO 1436, 3862, 4079 (rubber hoses), ISO 8331 (thermoplastic hoses)

• CSA Group: Various standards for Canadian applications

• Transport Canada: Regulations governing transportation applications

• CFIA: Food-grade requirements for processing applications

For Maritime industries, additional classification society requirements (DNV, Lloyd's, Bureau Veritas) may apply to marine installations. Understanding applicable standards early in the design process prevents costly redesigns and approval delays.

Partner with Sangster Engineering Ltd. for Your Fluid System Needs

Selecting the optimal hose and tubing for your fluid system requires balancing numerous technical factors against practical constraints of budget, availability, and operational requirements. The consequences of improper selection—from energy waste to equipment damage to safety incidents—make expert guidance invaluable.

Sangster Engineering Ltd. brings decades of mechanical engineering expertise to fluid system design challenges across Nova Scotia and Atlantic Canada. Our team understands the unique demands of our region's industries, from the fishing and marine sector to manufacturing and resource extraction.

Whether you're designing a new system, troubleshooting existing problems, or establishing maintenance programmes, our professional engineers provide the technical analysis and practical recommendations your project requires. We work with clients to optimise hose and tubing selections that deliver reliable performance, regulatory compliance, and cost-effective operation throughout the system lifecycle.

Contact Sangster Engineering Ltd. today to discuss your fluid system engineering requirements. Our Amherst-based team serves clients throughout the Maritimes with responsive, professional engineering services tailored to your specific application needs.

Partner with Sangster Engineering

At Sangster Engineering Ltd. in Amherst, Nova Scotia, we bring decades of engineering experience to every project. Serving clients across Atlantic Canada and beyond.

Contact us today to discuss your engineering needs.