Articles & Case Studies

PMP’s Eight hour window

Posted: Wednesday 9th July 2014

PMP were contacted by Yorkshire Water and alerted to an ongoing operational issue at Whitwood Sewage Pumping Station (transfers crude sewage to Normanton Waste Water Treatment Work’s in Castleford).

The dry-well submersible transfer pumps were worn and required removing to enable urgent maintenance. The non-return valves from the transfer pumps needed replacing but the rising main isolation valves were “jammed” in the open position on all three legs of the rising main manifold/pipe-work. As a consequence it was totally impractical to stop flows returning back to the pumping station thus preventing any maintenance activities on the pumps and NRV’s.

In order to rectify this issue the contents within the rising main required “freezing,” enabling the safe replacement of the isolation valves along with the non-return valves. The time required to complete this in addition to the need to work within a “confined space” were other significant factors that had to be considered to enable PMP to deliver a successful outcome for Yorkshire Water.

It soon became apparent that the flows into the pumping station had to be managed by non-pumping means and that the volume of flow to be transferred was critical to both project duration and cost. For this reason the decision was taken to wait for low flow conditions (period of dry weather) in order to minimise the diurnal impact. This allowed time for PMP to provide a detailed project brief and to plan for all contingency events. After consideration of the longer term weather forecast a suitable day was identified to complete the repairs and a number of pre-start activities were undertaken to mitigate other potential risks on the day.

The pumping station was drained down to its lowest level just after the morning peak flows had subsided, this level was maintained through the use of tankers to transfer incoming flow to Normanton treatment works. The isolation valves downstream of the pumps were closed to stop flows returning into the well from the rising main through the pumps. At this point a “line-freeze” was applied allowing the pipe-work to be cut between the main isolation valves and the outlet to the rising main. The fact that this was done upstream of the pump manifold allowed us to install one isolation valve common to all three pumps, following which the system was returned to its former parameters.

The remedial works were completed within an eight hour window and a successful outcome was achieved without compromising any of Yorkshire Water’s key business drivers (pollution to watercourse, flooding of properties etc). The solution provided by PMP now allows our client to isolate the pumping station from the rising main allowing any future maintenance activities to be undertaken quickly and cost effectively.

PMP also has excellent credentials for working by rope access above and below ground their Confined Space Rescue Team, survey work, frequently carried out on aqueduct pipelines, reservoir draw-off systems, sewers and culverts. In addition to engineering for penstocks, valves actuators and head-stock control gear, in-house workshops allow PMP to undertake bespoke projects. Fixtures and components are manufactured, with decking, guards and railings also fabricated and installed at water treatment works and reservoirs

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