Diesel Suction Hoses.

Suction hose carries a helical reinforcement — usually a steel or rigid plastic helix — that stops it collapsing under the vacuum created when a pump draws fuel.

Delivery hose has no such reinforcement because it only ever sees positive pressure. Using it on the suction side causes it to flatten, starving the pump.

The hose collapses under vacuum, restricting flow. The pump then cavitates — running partly on vapour rather than liquid — which causes noise, poor flow and rapid wear of the vanes or gears.

It is a common cause of premature pump failure and is often misdiagnosed as a faulty pump.

Limited by the pump's rated suction lift, commonly two to three metres of vertical lift for a typical transfer pump, with horizontal run adding friction losses on top.

Mount the pump as close to the fuel level as practical. If the pump must sit well above the tank, a submersible or foot-valve arrangement is more reliable.

Where the pump sits above the fuel level, yes. A foot valve holds prime in the suction line so the pump does not have to re-prime each time, which reduces dry-running and speeds up dispensing.

Without one, the line drains back between uses and the pump works hard on every start.

Yes. A basket strainer or foot valve with integral strainer keeps debris and larger particulates out of the pump. Fine filtration belongs downstream on the dispensing side.

Position the suction inlet slightly above the tank base so it does not draw the sediment and water that settle there.

Look for flattened or kinked sections that no longer round out, separation of the reinforcing helix from the wall, cracking, and any softening. Hose that has been driven over should be replaced.

A hose that has collapsed once will usually collapse again at the same point even if it looks recovered.