Articles & Case Studies

Linwood pumping station – a study in remote pump control

Posted: Wednesday 21st December 2011

Blockages are a frequent problem for sewage pumping stations, capable of causing serious damage to pumping equipment. We profile one pumping station in Scotland that was accruing massive maintenance costs and an innovative solution which is saving more than £100,000 per annum.

Pumping stations are notorious for pump blockages which at best can cause pumps to run less efficiently or at worst can result in total pump failure leading to continued stoppages and significant on-going maintenance costs.

A typical example of a blockage causing even more damage downstream regularly occurred at Linwood pumping station, near Johnstone to the West of Glasgow in Scotland.

Linwood is the main pumping station serving Johnstone treatment works which itself serves approximately 80,000 people in the area. Linwood is classed as a large critical station, but Scottish Water was finding that an abnormal amount of time was being spent repairing the three pumps at the site.

David White – Service Area Manager at Flygt in Scotland takes up the story. “Scottish Water was running up some very large repair bills due to pump blockage issues resulting in cavitation damage to the hydraulic ends of the pumps,” says White. “But, this was only part of the problem as the blockages were resulting in high operational costs because of continual unplanned site visits and tank cleaning due to settlement build up.”

Cavitation damage is the technical term for cavities or bubbles that form in the liquid that is being pumped. Cavities form at the low pressure or suction side of the pump and collapse when they pass into the higher regions of pressure, causing noise, vibration, and damage to many of the critical components of the pump.

“Linwood was equipped with three 210kW pumps and repair costs were running at a far higher rate than they would have liked.” says White.

“However, the costs did not stop there. Additional costs were incurred through unplanned breakdown visits organised to investigate blockages, organising cranes, employee costs and extra tank cleaning due to the continual failures of the station.

“The pumping station is situated on the flight path of Glasgow airport so approval was needed each time they had to erect a crane.”

Scottish Water turned to ITT WWW who carried out a full site survey and recommended the NP3312 pump, a 250kw pump which could cope with a high build-up of raggy materials, the main cause of the blockages in this extreme environment.

The new system incorporated the use of variable speed drive upgrades with Flygt Pump Smart software. In addition, an independent Flygt D7000 series remote telemetry unit (RTU) was fitted; it was then connected using MODBUS to a Flygt MAS pump monitoring unit providing vibration and temperature sensors from the pump.

The D7000 RTU was then remotely connected, through GSM, to Flygt’s Bureau service allowing Flygt to monitor in real time all pump sensors and station level control round the clock.

As part of the solution, Flygt engineers also recommended new control equipment to run alongside the existing system. “The new remote telemetry unit was needed in addition to the old telemetry system because it had the capacity to condition monitor the pumps, as opposed to giving only a trip signal if pumps had failed,” says White. “In this way we had a much greater knowledge about pump performance and could react to problems or maintenance issues before any failure.”

By installing MAS 711 units to protect each pump, together with vibration sensors, any blockage problems or cavitation issues could be spotted quickly and the pumps shut down prior to any major damage being caused.

The existing control system was re-programmed to incorporate cleaning cycles which reduced silt and debris build-up. Information from the existing PLC, including sump level from the ultrasonic sensor and running statistics was also monitored from Flygt’s Bureau service.

David concludes: “The Linwood solution massively reduced the high maintenance costs being experienced by Scottish Water and has given the customer much more control over the day to day running of the pumping station. We can now help them get ahead of problems rather than waiting for failure before reacting.”

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