Thames Water Operations at Deephams STW had a High-Level pump out of service for over 15 months due to the pump being blocked, the DN1000 gate valve situated on the suction line could not be closed due to rag and debris within the bonnet / suction pipework. Several other contractors had previously tried to close the suction valve using conventional methods but had been unsuccessful.
Gel Engineering were asked to come up with a solution, based on previous site experience and with consultations with the Deephams operational team 2 options were identified, both options involved a complete diversion of all flows from the High Level Pumping Station to the Powerhouse Pumping Station, this could only be achieved during the night at reduced flows.
Gel Engineering proposed two options:
• Option No1 – Make entry into wet well and clear suction valve / pipework through the pipes bellmouth
• Option No2 – Remove valve bonnet in dry well and de-rag then close suction valve.
Following discussions, it was agreed that option two would be used due to the risk and costs involved in a full confined space entry into a wet well that had not been entered in years, this option also had its issues.
• The High-Level Pumping Station dry well was approximately 25m in depth • The overhead crane could only be utilised to remove the pump • There was no access to the DN100 valve for the overhead crane.
Gel Engineering, using a 30m electric hoist with a 2 tonne cable and using the overhead crane as a lifting beam the team managed to remove the DN1000 gate valve bonnet. With the valve bonnet removed a vast rag build was removed approximately 1 tonne of rag / debris. The DN1000 gate valve was then closed completely allowing work on pump No3 to be de-ragged with safe isolation during the day shift The works were completed within 2 working days and No3 pump is now back in operation.
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