Mechanical installation work within a reservoir valve tower

• Delivery of complete turnkey solution
• Responsive and flexible service accommodating difficult installation
• Installation successfully completed under harsh conditions

Problem

Little Denny reservoir was constructed in 1888 with a capacity of 609,560m³ and a maximum depth of 13.4m. Following a statutory inspection of the dam under the Reservoirs Act 1975, Scottish Water was required to perform a number of upgrades to bring the site into compliance.

Scottish Water awarded a contract to GMJV to complete the necessary modification work who in turn issued a mechanical scope of work package for competitive tender.

Solution

Xm Services participated in the tendering process to deliver the necessary mechanical modifications and was awarded a contract by GMJV which included the following scope of work:

• Supply and installation of a new DN400 outlet valve at the bottom of the valve tower
• Design, manufacture and installation of an extension spindle to enable the new valve to be opened and closed without having to enter a confined space
• Design, manufacture and installation of a new 15m long valve tower access ladder with extendible stringers

The new valve weighed 380kg which meant that it needed to be lifted into position and installed using a crane. However access restrictions on top of the dam head, the poor structural integrity of the existing valve tower bridge and the reservoir bed's unstable ground conditions meant that GMJV were only able to build an access road on the reservoir bed to the base of the valve tower. In order to assist GMJV with building a suitable access road Xm Services worked with a subcontractor, undertaking a site survey and providing a lift plan that illustrated the required working area and ground loadings.

Due to the confined nature and age of the cast iron valve tower Xm Services' performed a detailed inspection to determine the site specific risk assessments and method statements. On completion of the inspection it was determined that it was not possible to safely erect a scaffold structure around the outside of the valve tower in order to drill mounting holes through the valve tower wall and mount the access ladder and spindle support brackets. As a result Xm Services identified an alternative method of installation using a small man basket suspended from the crane in order to work at height inside and outside of the valve tower.

Little Denny Reservoir ø5ft Valve Tower

During the project there were some additions and changes to the scope of work associated with the installation and Xm Services proactively worked with GMJV to address the issues without hindering project progress. Some of the examples include:

• Prior to Xm Services commencing work on site GMJV discovered an existing penstock was obstructing the outlet pipe from being lined at the base of the valve tower. Xm Services mobilised an engineering team to visit site and remove the penstock so that the outlet pipe could be lined without the project incurring any delay.
• When Xm Services were installing the new valve it was discovered that there was misalignment between the aqua grip and the pipe flange which meant that (4-off) M27 stainless steel bracing rods could not be fitted. To overcome the misalignment Xm Services provided and installed (8-off) M20 stainless steel bracing rods the next day.
• On completion of the pipework installation the customer requested that a new screen was fitted at the end of the outlet pipe to prevent the ingress of debris. Following receipt of the request Xm Services designed, manufacture and installed a new galvanised steel screen within a week enabling the reservoir to be reinstated quickly.

Benefits

Through undertaking the project Xm Services was able to deliver a local and responsive mechanical engineering service along with using its effective relationships with its subcontractors to deliver a turnkey solution.

Good service from Xm Services working in harsh conditions – Colin Grier, Site Agent, GMJV