Effective Inlet Configuration
Effective inlet configuration plays a significant role. High inlet positions should be avoided to avoid cascading which causes turbulence and air entrainment which can reduce pump efficiency by as much as 10 to 15%. Ideally the inlet should be at a low level, where this is not possible, a high-baffle or drop pipe should be used. The inlet should be opposite and square-on to the pumps to reduce the risk of bulk rotational flows. These flows, especially if going in the opposite direction to the impeller’s rotation, can cause significant problems.
Well Construction
The shape of the well is also important and the flat floor area within the well should be minimal. This can be achieved by sloping the base of the well by 45 to 60 degrees as this sloping will move the debris naturally towards the pumps. Creating a small residual sump area around the pump intake will allow maximum debris clearance and care should be taken with any irregular well shaping or sloping to avoid creating surface or sub-surface vorticity, which can lead to air entrainment.
It’s important to consider the properties of the pumped media. High rag and fibre content, grit, fat, oil and grease should all be expected, but more unusual hard objects sometimes make an appearance. This is when a large free passage pump becomes even more important.
Correct Pump Selection
The correct pump selection can really boost a system’s performance. Knowing and utilising the pump’s Best Efficiency Point (BEP) is crucial and ideally the highest utilisation duty point should occur between 80 and 105% of the pump’s BEP as anything outside this range can lead to increased operational & maintenance issues, increasing the cost of ownership for the end user.
Both the pump and the pumping station should be of a resilient design capable of continuously removing floating, suspended and settled solids. The vertical discharge riser pipework should be sized to ensure a minimum flow velocity of 1.5 metres per second during the cleaning-cycle as levels approach the bottom water level stop-point.
Pump Level Control
Finally pump level control also plays a key role. The longer or more frequently the pump operates at low level, the cleaner the wet well becomes and a cleaner wet well means less pump blockages and higher efficiency.
By following a combination of good inlet configuration, well construction, pump selection & control you’ll be able to improve your designs, reduce blockages and improve efficiency.
