Suction and Return Line Hose

What it is

Low-pressure hydraulic lines fall into two groups. Suction lines run from the reservoir to the pump inlet. The pump pulls oil through them, so the hose is under partial vacuum and must not flatten. Return lines carry oil from valves and actuators back to the tank at low pressure. SAE J517 defines the common types. SAE 100R4 is the standard suction and return hose. Low-pressure braided hoses such as 100R3 and 100R6 are used for return lines and other low-pressure service but are not suction hoses.

How to identify

Suction hose such as 100R4 is thick and somewhat stiff, with a wire helix you can feel through the cover and often see as ridges. It is built of an oil-resistant rubber tube, textile plies, the embedded helix wire and a rubber cover. The layline names the SAE type, size and maker. Braided low-pressure hose is thinner and flexible, with no helix.

Hose types for low-pressure lines

Sizing a suction line

Suction lines are sized larger than pressure lines because pumps are sensitive to inlet restriction. Oil velocity in a line can be found from flow and inside area:

Velocity (ft/s) = 0.3208 × flow (gpm) ÷ inside area (sq in)

Pump makers state the inlet velocity and vacuum limits their pump can tolerate. Size the hose to stay within them. Too small a suction line causes cavitation, noise and early pump failure.

Key points

• Suction hose needs a fitting that grips without crushing the helix. Use couplings and hose ends specified for that hose type, usually with clamps or crimp ferrules made for it.
• Every connection on a suction line must be air tight. A small leak lets air in and causes aeration and pump damage.
• Check the maker's vacuum rating and minimum bend radius. Kinking or bending too tightly reduces the inside diameter and can collapse the hose.
• Return lines can see pressure spikes. Use a hose rated for the line, not just "return hose."

Common mistakes

• Using a braided 100R6 hose on a pump suction. It can collapse and starve the pump.
• Downsizing a suction line to match the pump inlet fitting size without checking flow velocity.
• Over-tightening hose clamps on suction hose until they cut the cover.
• Ignoring a loose suction fitting because it does not drip oil.

Governing standards: SAE J517 (hydraulic hose); pump manufacturer inlet requirements; hose manufacturer ratings.

Reference only. Verify against the current governing code or standard, the manufacturer's data and the project documents before use. Apps for Distributors disclaims liability arising from reliance on this reference.