Short answer
A discharge hose must be suitable for internal pressure, while a suction hose must be suitable for the external-internal pressure difference in the application. A high positive working pressure rating is not a guarantee against collapse under vacuum. For a product that will handle both suction and discharge, both services must be stated explicitly.
Technical explanation
During suction, the internal pressure of the hose drops relative to its surroundings; maintaining the cross-section is important for flow. A helix in the product construction can be a useful design feature, but on its own it does not prove a specific vacuum resistance. Vacuum capacity may include limits that depend on size, temperature and bending. In a discharge line, the pressures created by the pump, valve movements and process transitions are taken into account. The direction in which the line is normally used is not the same thing as all operating conditions.
Topic-specific checkpoints
| Item | Description |
|---|---|
| Discharge service | Normal and peak internal pressure; product limits together with temperature. |
| Suction service | Vacuum or absolute pressure; size, temperature and bending conditions. |
| Bidirectional use | A separate condition row for each operating state. |
| Shape retention | Helix/reinforcement construction and the manufacturer's statement of suction suitability. |
How is it assessed in practice?
When assessing a tank unloading line, take the phrase 'on the pump suction' as initial information; request the reference for the absolute pressure or vacuum value separately. Then transfer the hose length, transition cross-sections and routing to the drawing. If the same hose is occasionally used in the reverse direction for filling, add the second operating state to the file. Rather than trying to solve cross-section narrowing with a larger diameter alone, also verify that the hose is designed for suction.
Original editorial recommendation; not a clause of a standard.
Frequently asked questions
Can every steel wire hose be used for suction?
No. Wire braid, helix and other reinforcement constructions do not serve the same function. Look for the suction capacity and conditions of the product code; do not determine a vacuum class from appearance.
Source coverage
-
S017
Parker Safety Guide, Publication 4400-B.1 Parker Hannifin · accessed 2026-10-20 PDF page 2; 2.3 Suction | PDF page 2; 2.7 SizePDF page 2; 2.3 SuctionPDF page 3; 3.7 Minimum Bend Radius, 3.8 Twist Angle and Orientation and 3.13 Routing | PDF page 2; 2.3 Suction | PDF page 2; 2.4 Temperature | PDF page 3; 2.17 Radiant HeatPDF page 2; 2.8 Routing, 2.10 Mechanical Loads and 2.11 Physical Damage | PDF page 2; 2.2 Pressure
-
S036
Industrial Hose Safety Connections Gates · accessed 2026-10-19 PDF pp. 6–8 construction and selection; pp. 10–19 maintenance; pp. 21–27 special services