Suction hose resists collapse under vacuum thanks to an embedded helix; discharge hose resists internal pressure thanks to textile or wire reinforcement, the two are not interchangeable. Put a discharge hose on a pump inlet and it flattens the moment the pump pulls vacuum; put a light suction hose on a high-pressure outlet and it bursts. If one line alternates between priming (vacuum) and pumping (pressure), specify a combined suction-and-discharge hose rated for both duties.
This comparison explains the construction difference, the specifications that matter on a purchase order, and the decision rules for choosing between the two, written for procurement and maintenance engineers who buy on parameters, not adjectives.
What is the difference between a suction hose and a discharge hose?
A suction hose works below atmospheric pressure (typically −0.5 to −0.9 bar) and is built around a rigid steel or plastic helix that stops the wall collapsing inward. A discharge hose works above atmospheric pressure and is built with textile or wire plies that stop the wall bursting outward.
On the suction side of a pump, the pressure inside the hose is lower than the atmosphere outside. Without a supporting helix, external air pressure crushes the bore, a vacuum of only −0.3 bar can permanently crease a standard delivery hose, choking flow and starving the pump. Vacuum resistance is verified by the test method of ISO 7233 (determination of resistance to vacuum for hoses and hose assemblies).
On the discharge side, the load is reversed: internal pressure tries to expand and burst the wall. Here the governing figures are working pressure, burst pressure and, for dynamic duty, impulse resistance. A helix adds nothing on this side except weight, stiffness and cost.
How do the constructions compare?
Both families share the same three-layer logic, inner tube (media contact), reinforcement (mechanical strength), outer cover (environment), but the reinforcement diverges completely.
| Type | Duty | Reinforcement | Vacuum rating | Typical WP (DN 50) |
|---|---|---|---|---|
| PVC suction hose, rigid PVC helix | Suction | Hard PVC spiral | Full vacuum (−0.9 bar) | 4–7 bar |
| Rubber water suction hose | Suction | Steel wire helix + textile plies | Full vacuum (−0.9 bar) | 6–10 bar |
| Layflat discharge hose | Discharge | Circular-woven textile | None | 8–15 bar |
| Rubber delivery hose | Discharge | 2–4 textile plies | None | 10–20 bar |
| Chemical S&D hose (EN 12115) | Both | Textile plies + embedded wire helix | −0.9 bar | 16 bar |
| Tanker S&D hose (EN 1765) | Both | Textile + helix, heavy wall | −0.9 bar | 10–15 bar |
Two consequences of the helix are routinely overlooked at the design stage:
- Bend radius. A wire-helix suction hose of a given DN typically needs a 40–60 % larger bend radius than a plain delivery hose of the same bore. Check the routing before brackets are welded.
- Fitting retention. Heavy-wall suction and S&D hoses are normally secured with bolted safety clamps to EN 14420-3 (DIN 2817) or swaged couplings matched to the hose wall, not with light worm-drive clips. On chemical and tanker hoses the clamp type is dictated by the product standard.
Working pressure always falls as DN rises within a hose family, never carry one pressure figure across a size range. All elastomer hose ratings are quoted at +20 °C and derate with temperature.
Which specifications must be on the purchase order?
As a minimum: bore (DN), working pressure at operating temperature, vacuum rating (suction side), tube compound, temperature range, end fittings with clamp type, and the applicable product standard.
| Parameter | Suction hose | Discharge hose | Reference |
|---|---|---|---|
| Working pressure (DN 50, typical) | 4–10 bar | 8–20 bar | Product standard / datasheet |
| Burst : working pressure ratio | ≥ 3:1–4:1 per product standard | ≥ 3:1–4:1 per product standard | e.g. EN 12115 |
| Vacuum rating | −0.5 to −0.9 bar | Not rated | ISO 7233 test |
| Pressure test method | Hydrostatic proof ≈ 1.5 × WP | Hydrostatic proof ≈ 1.5 × WP | ISO 1402 |
| Temperature (EPDM tube) | −30 to +90 °C | −30 to +90 °C | Datasheet |
| Temperature (NBR tube) | −25 to +80 °C (oils/fuels) | −25 to +80 °C | Datasheet |
| Flow velocity guideline | ≤ 3 m/s (avoid cavitation) | ≤ 6 m/s | Design practice |
Note that ISO 1402 defines the hydrostatic test methods (proof and burst); the required safety factor comes from the product standard for the hose type, for example EN 12115 for chemical S&D hose. Do not quote a safety factor without naming its source, and never treat burst pressure as an operating reserve.
Tube compound follows the medium, not the hose type: NBR for fuels and mineral oils (not hot aromatics), EPDM for water and chemicals (never oils or fuels), UPE for concentrated acids and alkalis, PTFE-lined constructions for near-universal chemistry. Food-contact hoses need certification for the specific medium: EC 1935/2004 plus FDA 21 CFR 177.2600 for rubber compounds (PTFE liners fall under 21 CFR 177.1550).
Which standards apply?
- ISO 7233, vacuum resistance test method for hoses and assemblies; the reference for any declared vacuum rating.
- ISO 1402, hydrostatic testing (proof and burst) of hoses and hose assemblies.
- EN 12115, rubber and thermoplastic hoses for liquid and gaseous chemicals; covers S&D types, 16 bar class, electrical resistance requirements.
- EN 1765, rubber hose assemblies for oil suction and discharge (tanker/terminal service).
- EN 14420-3 / DIN 2817, bolted safety clamps for hose fittings.
For fuels and solvents, electrical continuity matters: electrical resistance is tested to ISO 8031, and conductive or electrically bonded assemblies (marked M or Ω) are required in ATEX zones per 2014/34/EU.
When do you need a combined suction-and-discharge hose?
Whenever one line sees vacuum during priming and positive pressure during pumping, tanker offloading, portable pump sets, dewatering, irrigation headers. A combined S&D hose carries both a helix and pressure-rated plies, so it is rated for, say, −0.9 bar vacuum and 10–16 bar working pressure in one construction. Dedicated suction or discharge hoses individually cannot cover both conditions.
The combined construction costs 15–25 % more than a plain suction hose, but it removes the most expensive failure mode of all: a field crew installing the cheaper discharge hose on the vacuum leg. Browse suction and discharge hoses in the industrial hose range or run a search for suction hose to compare vacuum-rated constructions.
Selection decision rules
- Map the pressure regime first. Suction only → helix hose. Discharge only → ply-reinforced hose. Alternating → combined S&D.
- Size the bore from velocity. Keep suction lines at or below 3 m/s to avoid cavitation; discharge lines at or below about 6 m/s to control pressure loss.
- Rate for pump shut-off, not nominal duty. On the discharge side, the hose must cover maximum pump shut-off pressure with margin, at the actual operating temperature.
- Verify the declared vacuum rating (ISO 7233 basis) against the deepest vacuum the pump can pull, typically −0.8 to −0.9 bar for self-priming units.
- Match tube compound to the medium including cleaning media; check the manufacturer's resistance table, not a generic elastomer chart.
- Specify fittings and clamp type together with the hose, bolted safety clamps (EN 14420-3) for heavy-wall and safety-critical media; the fitting supplier needs the exact hose OD and wall.
- Demand documentation: proof-test certificate, vacuum rating, batch traceability. It will be asked for at the next audit.
Fitting hardware for both hose families, shanks, clamps, couplings, is covered in the industrial fittings category.
Inspection and failure modes
Suction hoses fail by bore deformation (permanent inward creasing after a vacuum event beyond rating) and helix corrosion where moisture reaches the embedded wire through a damaged tube; inspect the bore visually at each service and replace at the first sign of creasing or wire staining. Discharge hoses fail by cover cracking (ozone/UV), tube erosion in abrasive media and blow-off at fittings from mismatched clamps. For both, kinks, exposed reinforcement or sticky/hardened covers are immediate replacement criteria, inspect every 6–12 months depending on duty severity.
For deeper background on constructions and standards, see the complete suction and discharge hose technical guide and the specification-pitfall guide for engineers.
Need the right hose on the first order?
Send us the medium, bore, pressure and vacuum figures, and required fittings, our engineering team selects the hose and fittings, assembles them, and pressure-tests the complete assembly before dispatch. Browse the industrial hose range, check the technical catalogues, or request a quotation directly.