Where hoses are used on compressors
Hoses appear in more places on a compressor than most people realise, and each circuit places different demands on them.
| Circuit | What the hose sees | Key selection points |
|---|---|---|
| Oil circuit (screw compressor) | Hot oil at system pressure, pulsation, vibration | Oil-compatible tube, temperature rating above normal oil temperature with margin, correct fittings |
| Airend discharge to separator | Hot air and oil mist at full pressure | High temperature rating; often a braided or metallic flexible as the maker specifies |
| Control and pilot air lines | Low flow, system pressure, moderate heat | Small-bore nylon or rubber tube with correct push-in or compression fittings |
| Cooling water (water-cooled machines) | Water, sometimes treated, moderate pressure | Water-resistant tube; secure clamping |
| Fuel and engine hoses (portable diesels) | Diesel, engine heat, vibration, dust | Fuel-rated hose and fittings; heat shielding |
| Site air hoses (portable compressors) | Compressed air to breakers, drills, blasting pots and rigs; drag, abrasion, sun | Working pressure above compressor maximum, abrasion-resistant cover, safe couplings and whip checks |
What a hose rating really means
Every hose has a maximum working pressure and a temperature range, set by its maker at a stated design factor between working pressure and minimum burst pressure. For industrial air and oil hoses that factor is commonly about 4:1, but it varies by standard and hose type, so the maker’s data is the authority.
Three points are often missed:
- Temperature reduces pressure capability. Many hoses lose rated pressure as temperature rises, and a screw compressor’s oil and discharge circuits run hot continuously, about 75–95 °C at normal discharge, with higher peaks on a hot day or with a fouled cooler.
- The fitting has its own rating. A hose rated for high pressure is limited by a fitting rated for less.
- Pulsation and surges count. Pressure spikes during loading, unloading and blowdown can exceed steady pressure and shorten hose life.
Pressures should be checked in both units where hoses are imported: 7 bar is 101.5 psig, 10 bar (145 psig), 14 bar (203.1 psig) and 24 bar (348.1 psig).
Fittings and assembly method
The joint between hose and fitting is where most assemblies fail. Permanent crimped fittings must come from the hose maker’s matched system, or from a fitting system approved for that hose, and be crimped to the specified diameter with the correct dies. Mixing a hose from one maker with fittings from another, or crimping by eye, can produce a joint that holds on test but blows off later under heat and vibration.
- Match the thread form exactly: BSP parallel, BSP taper, JIC, ORFS, metric and NPT look similar but do not seal together.
- Check the sealing method: O-ring face, cone, bonded washer or thread sealant.
- Use reusable or clamp-type fittings only where the hose maker and the duty allow it.
- Never use worm-drive jubilee clips on pressurised oil or high-pressure air hoses.
- Tag each assembly with its part number or specification and the date it was fitted.
Routing, bend radius and protection
A correctly rated hose still fails early if it is badly installed. Good routing practice includes:
- Respect the minimum bend radius, and avoid bends right at the fitting; allow a straight length before the bend.
- Do not twist the hose during fitting; use the lay line printed along the hose as a guide.
- Allow a little slack for movement and pressure-related length change, but not so much that the hose sags onto hot or moving parts.
- Keep hoses away from exhaust manifolds, turbochargers and hot airend surfaces, or fit heat sleeves.
- Clamp hoses so they cannot rub against each other, the frame or the enclosure; abrasion is a leading cause of failure on portable diesels.
- On site, route air hoses away from vehicle traffic and protect them where they cross roads.
Site air hoses on portable compressors
On construction, borewell and blasting work, the hose between compressor and tool is the most abused part of the system. It is dragged over rock, run over by vehicles, left in the sun and connected and disconnected many times a day. Particular care is needed:
- Use hose rated above the compressor’s maximum pressure, especially for borewell and DTH duties at 200–400 psig (13.8–27.6 bar).
- Size the bore for the flow and length; undersized hose wastes pressure and starves tools.
- Fit whip checks (safety cables) across every coupling and at the compressor outlet, and use couplings with safety locking.
- Close the compressor service valve and vent the hose before disconnecting a coupling.
- Inspect daily for cuts, bulges, exposed reinforcement and damaged couplings.
Typical tool demand helps with hose sizing: breakers and rock drills each use about 85–145 cfm at about 7 bar (101.5 psig), and blasting nozzles use far more as nozzle size increases.
Pressure drop in long site hoses
Hose bore and length matter as much as rating. Air loses pressure through every metre of hose and every coupling, and the loss rises steeply as flow increases. A compressor showing 7 bar (101.5 psig) at its gauge can deliver noticeably less at a breaker on the end of a long, small-bore hose, and the tool then hits more weakly and more slowly, or stalls. The usual fixes are a larger bore, a shorter run, fewer couplings, or a manifold near the work face with short whips to each tool. When we prepare a rental machine, we ask for the hose run length and the tools connected so that the hose set is sized for the job rather than for the compressor outlet alone.
Signs a hose must be replaced
| Sign | What it usually means |
|---|---|
| Cracks in the cover, hardness | Heat or ozone ageing; end of life |
| Bulges or blisters | Reinforcement damage or fluid getting between layers |
| Exposed braid or wire | Abrasion has broken through the cover; risk of rapid failure |
| Weeping at the fitting | Poor crimp, wrong fitting, or fitting movement |
| Kinks or flattening | Bend radius exceeded or crushed; internal damage likely |
| Soft, swollen tube | Fluid not compatible with the hose material |
A hose showing any of these should be taken out of service, not repaired with tape or clamps. Many plants also replace critical oil and discharge hoses at a set interval during major services, as the compressor maker advises, rather than waiting for visible damage.
Safety boundaries
A failing pressurised hose can whip violently or spray hot oil, which can ignite on hot surfaces. Before any hose work, stop the compressor, isolate it electrically or shut down the engine, and make sure the system is fully depressurised, including the separator tank and receiver. Allow hot oil to cool. Hose assembly crimping should be done by trained people with the correct equipment and data. Never use compressed air to clean skin or clothing, and never point an air hose at a person.
How Reddy Compressors helps
Reddy Compressors supplies compressor spare parts, including oil-circuit hoses, discharge flexibles, control tubing and site air hoses with couplings and whip checks, for ELGi, Atlas Copco, Ingersoll Rand, KAESER, Chicago Pneumatic, Sullair, Doosan, Kirloskar and other makes. We are an independent multi-brand specialist, not an authorised dealer, and we identify each hose from the machine’s make, model, serial, nameplate and the old assembly, confirming fit before quoting. We have tie-ups with all major and reputed brands. Parts are supplied across India.
Our rental compressors, from 50 to 2,000 cfm and 2 to 30 bar, are sent out with suitable hoses and fittings for the job, and on hire jobs our team services the machine every 300 running hours, including hose inspection. Our service engineers, based at Tarnaka, Secunderabad and covering Telangana and Andhra Pradesh, inspect and replace hoses during routine service and overhaul.
What to send us
- Compressor or engine make, model and serial number, with a nameplate photo.
- Photos of the hose in place, both end fittings and any marking on the hose.
- Hose length, bore and the circuit it serves.
- Working pressure and temperature, and the fluid it carries.
- For site hoses: the tools or rig being supplied and the hose run length.
Frequently asked questions
Why does my compressor oil hose keep bursting?
Repeated oil hose failures usually point to a cause beyond the hose itself. Typical reasons are oil running hotter than the hose rating because of a fouled cooler or high ambient temperature, a hose or fitting not rated for the pressure, a poor crimp, rubbing against the frame, or a tight bend near the fitting. Check the oil temperature, the routing and the hose specification before fitting another one.
What pressure rating should a portable compressor air hose have?
The hose’s maximum working pressure should be above the compressor’s maximum discharge pressure, including any safety valve setting, at the temperature it will see. For a typical 7 bar (101.5 psig) construction compressor that is straightforward, but borewell and DTH compressors run at 200–400 psig (13.8–27.6 bar) and need properly rated high-pressure hose and couplings with whip checks fitted.
Can I use any hydraulic hose on a compressor?
Not without checking. A hydraulic hose may have a high pressure rating but a tube compound or temperature limit unsuited to compressor oil or hot air and oil mist. The fittings, thread form and sealing method must also match. Use hose specified for the circuit by the compressor maker or an equivalent confirmed for the same fluid, temperature, pressure and pulsation.
What is a whip check and is it needed?
A whip check is a steel safety cable fitted across a hose coupling or between the hose and the compressor outlet. If the coupling separates under pressure, it stops the hose end whipping around and injuring people. Whip checks are strongly recommended on all site air hoses, especially at higher pressures, alongside proper locking couplings and venting the hose before disconnection.
How often should compressor hoses be replaced?
Replace any hose immediately if it shows cracks, bulges, exposed reinforcement, leaks at fittings or kinking. Beyond that, follow the compressor maker’s service schedule, which often calls for replacing critical oil and discharge hoses at major services because they age internally before damage shows. Site air hoses should be inspected daily and replaced as soon as their cover or couplings are damaged.
Why do new hoses leak at the fitting?
Leaks at a new fitting usually mean a mismatch or an assembly fault. Common causes are a thread form that looks similar but is different, a missing or wrong sealing washer or O-ring, a fitting from a different system than the hose, an incorrect crimp diameter, or overtightening that damaged the seat. Identify the port thread and sealing method before ordering a replacement.
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Technical content reviewed by D. Srinivas Reddy, Managing Partner and service engineer, Reddy Compressors. Last updated 17 October 2026. How our engineering content is reviewed.