AODD pumps generate pulsating flow. Every stroke pushes a slug of fluid through the outlet — not a smooth stream. If you hard-pipe straight into the pump manifold with rigid metal or rigid plastic connections, those pulse forces have nowhere to go. They transfer directly into the pump body, the manifold flanges, and the pipe joints. The manifold cracks. Fittings loosen. Flanges leak. And if the pipework is heavy enough, the pump body itself carries the structural load — which it was never designed to do.
The Fluimac Phoenix manual is explicit on this: both suction and discharge connections must be made with flexible hose. This is not a suggestion. It is a mandatory installation requirement.
What Rigid Connections Actually Do
Three failure mechanisms occur when AODD pumps are hard-piped:
Vibration fatigue. Each stroke creates a pressure pulse and a corresponding mechanical impulse. With flexible hose, the hose absorbs and dampens this. With rigid pipe, the impulse travels through the entire connected pipework. At joints, threads, and flanges, this cyclic loading causes fatigue cracking over time — not immediately, but predictably. The pump that seems to be holding after a rigid installation is slowly accumulating fatigue cycles until something gives.
Structural overloading. Rigid pipework is often heavy. When bolted directly to the pump manifold, the pump ends up mechanically supporting the weight of the pipe run. The pump manifolds — particularly in PP or PVDF — are designed to handle fluid pressure and connection loads from flexible hose, not the cantilever weight of a rigid pipe system. Over time the manifold distorts, flanges pull out of true, and leak paths develop.
Pipe movement transfer. Industrial pipework expands and contracts with temperature. It also moves when valves are slammed, when pressure spikes occur elsewhere in the system, or when the surrounding structure moves. All of that movement, in a rigid-connected system, transfers directly to the pump. Flexible hose isolates the pump from the rest of the system.
The Correct Hose Specification
The hose must be chemically compatible with the fluid being pumped — the same compatibility check you did for the pump’s wetted materials applies to the hose as well. For aggressive chemicals (acids, solvents, oxidisers), PTFE-lined flexible hose is typically required. For less aggressive duties, rubber-lined hose in compatible grades may be acceptable.
The hose must also be rated for the operating pressure — check maximum air supply pressure against hose working pressure rating with appropriate safety factor. And the hose length must be sufficient to allow the pump to move slightly under operation without pulling the hose taut. A hose that’s too short defeats the purpose of having a flexible connection.
Suction Hose Considerations
On the suction side, the hose must not collapse under the negative pressure the pump generates during the intake stroke. Standard flexible discharge hose often has insufficient wall stiffness to resist suction collapse. For suction duty, use reinforced hose designed for vacuum service — wire-reinforced or spiral-reinforced PTFE hose is common for chemical applications.
A collapsed suction hose looks like a cavitation or starvation problem from the outside — the pump cycles but flow is erratic, and the pump may stall under load. It’s frequently misdiagnosed as a pneumatic exchanger fault or a snap-on fitting restriction. Check the suction hose first: squeeze it by hand at the connection point while the pump is running. If it collapses perceptibly during the intake stroke, the hose is the problem.
Supporting the Pipe Run
Flexible hose at the pump connection does not solve the problem if the first rigid section immediately after the hose is unsupported and heavy. The pipe run after the flexible section must be properly supported so that its weight and movement are carried by the pipe supports, not transmitted back through the hose to the pump. The pump should never be the structural support for any section of the connected pipework.
If you’re commissioning a Fluimac Phoenix installation and want guidance on hose specifications for your specific chemical duty and pressure requirements, contact us at info@autoflotechnology.com.