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Short answer: If an AODD pump’s suction hose flattens while it is running, stop the pump and isolate the liquid before restarting. The hose may lack a suitable vacuum rating, or the pump may be pulling against a blocked, undersized, kinked or otherwise restrictive inlet. Replace a damaged hose with a chemically compatible, non-collapsible suction hose and remove the restriction. Do not assume that a stronger hose alone will fix an obstructed system.
A collapsing hose reduces the inlet area just when the pump needs liquid. Flow can fall, priming can become erratic and the pump can cycle while delivering little product. The WILDEN P100 catalog photograph associated with this guide shows a real AODD pump, but it is representative; identify the actual pump and hose before specifying parts.
How to recognize suction-hose collapse
Watch the hose during a controlled start from a safe position. A soft section may flatten near the pump, at a bend, or beside a coupling, then return to shape when the pump stops. Sometimes the outside looks normal while a loose inner liner folds inward. Compare the flow, cycle rate and inlet condition before and after the symptom appears. A pressure-rated discharge hose is not automatically suitable for vacuum service.
Distinguish hose collapse from an air leak. A leaking joint often admits air and makes priming unstable without visibly flattening the hose. A blocked inlet or closed valve can create the vacuum that collapses an otherwise marginal hose. If the pump has never delivered liquid after installation, first check the source level, valve position and suction routing. For broader priming faults, see DFIN’s WILDEN P100 priming guide.
Why does the hose collapse?
The hose is not built for suction
A thin, unreinforced or lay-flat hose may carry a positive-pressure rating yet deform under inlet vacuum. Heat, chemical exposure, age and an over-tight clamp can reduce its resistance further. Check the supplier’s continuous vacuum rating at the actual operating temperature, along with liner, cover and reinforcement compatibility. Do not infer suitability from the hose’s pressure rating alone.
The inlet path is too restrictive
A clogged strainer or foot valve, closed or partly closed isolation valve, kink, sharp bend, blocked tank outlet or undersized fitting can starve the pump. A long suction run and excessive lift add losses; higher viscosity makes the problem worse. WILDEN’s installation guidance calls for suction pipe at least as large as the pump inlet and a reinforced, non-collapsible hose. Treat that as a starting point, then check the complete line and the model-specific manual rather than selecting by port size alone.
The pump is being driven faster than the inlet can feed it
High air input can raise cycling demand even when the liquid arrives slowly through a difficult suction line. Reducing the air setting under controlled conditions can help diagnose starvation, but it cannot make an unsuitable hose safe. Check the actual duty point and air supply against the pump’s published curves. If adequate flow requires an unacceptable suction arrangement, revise the installation or pump selection.
Safe diagnosis in a useful order
- Stop and make safe. Close and isolate the air and liquid systems, relieve trapped pressure, follow lockout procedures and use protection appropriate to the fluid. Do not loosen a chemical hose while it is pressurized or full.
- Record the symptom. Note whether the hose flattens only while running, where it flattens, source level, fluid temperature, viscosity, air setting and observed flow. Photograph the whole suction route and the hose markings.
- Inspect the easy restrictions. Confirm the suction valve is fully open; inspect the strainer, tank outlet, foot valve, bends and couplings. Look for a liner that has separated internally even if the outer cover appears round.
- Check dimensions and lift. Compare the hose’s actual inside diameter with the pump inlet and check long runs, reducers and high points. Confirm the suction lift and fluid conditions against the exact pump manual. Do not rely on the nominal hose outside diameter.
- Verify hose specification. Obtain the manufacturer’s vacuum rating, temperature range, minimum bend radius and full wetted-material list. Confirm chemical compatibility for the actual concentration and temperature.
- Test after correction. Reassemble with supported, airtight joints and a suitable hose; then start at a controlled air setting. Observe hose shape, priming, stable flow and leaks. If the hose remains round but flow is still poor, continue with suction-side and check-valve diagnosis instead of repeatedly increasing air pressure.
Match the observation to the next action
Swipe the table horizontally to view all columns.
| Observation | Likely area to check | Next action |
|---|---|---|
| Hose flattens only while pumping | Vacuum rating, local bend or inlet restriction | Stop; inspect hose specification and upstream line |
| Hose stays round, but pump loses prime | Air leak, lift, empty source or check valves | Check airtight joints, liquid level and wet-end condition |
| Flow falls as source level drops | Increasing suction lift, vortexing or restricted pickup | Review pickup submergence and permitted lift |
| Problem appears with a colder or thicker batch | Higher viscosity and suction losses | Record temperature and viscosity; reassess line and pump duty |
| Outer hose looks sound but flow remains restricted | Detached inner liner or hidden blockage | Isolate and inspect the full hose bore |
Choose a replacement suction hose and pump arrangement
Specify a hose for vacuum, chemical service and the full temperature range. State the required inside diameter, working length, bend radius, connection standard and support method. The liner, reinforcement, seals and fittings all need to suit the fluid. A reinforced hose can still be wrong if the liner swells, the coupling necks down the bore, or the route forces a tight bend.
Keep the suction route short and direct where practical. Support the hose so it does not pull on the pump manifold. Avoid a small reducer at the pump inlet; it can erase the benefit of a larger hose. If solids are present, specify a strainer or pickup arrangement that protects the pump without creating unacceptable restriction, and plan access for cleaning. For chemical transfer, review DFIN’s chemical-processing application page and WILDEN pump catalog alongside the actual operating data.
Replacement of the hose is a system decision, not proof that the pump is defective. If a correctly specified hose continues to collapse, investigate blockage, lift, line sizing and operating speed. If the inlet is clear but the pump still lacks flow, inspect the wet end using the exact service manual and identify any required parts through DFIN’s parts catalog.
What to send with an RFQ
Provide the full pump nameplate and configuration code, not just a family name or a representative photo. Include the liquid and concentration, operating and cleaning temperatures, viscosity, solids, container level range, suction lift, hose ID and length, existing hose markings, connection sizes, required flow and discharge pressure, available air supply and photographs of the installation. State whether you need a hose, fittings, strainer, pump review or wet-end service parts. These details let the supplier check compatibility and the entire suction duty before quoting. Cost depends on materials, construction, size, connections and quantity; request a configuration-specific quotation through DFIN’s RFQ page.
FAQ
Can I use a discharge hose on the suction side?
Only if its supplier explicitly rates that exact hose for the required vacuum, fluid and temperature. A positive-pressure rating by itself is insufficient. Ordinary lay-flat hose is especially unsuitable when it can flatten under suction.
Will a thicker hose solve low flow?
It can solve collapse caused by an inadequate hose, but it will not clear a blocked strainer or closed valve. Verify the inlet path and operating conditions before replacing components.
Should I increase air pressure to recover flow?
No. Extra cycling demand can worsen starvation and hides the cause. Confirm the inlet is open and the hose holds its shape, then operate within the exact pump’s published limits.
Do I need to replace the pump?
Usually diagnose the hose and suction system first. If a suitable, clear suction line still cannot meet the duty, compare the required flow, lift and fluid properties with the exact pump configuration and ask for a selection review.