AJT: Automatic Self-Closing Valve (ASCV) Replacement

AJT were contracted to design, supply and install a new, bespoke 96” (2438mm) Automatic Self Closing Valve (ASCV), manufactured and supplied by VAG-Group in Germany. This was to replace the existing 1950’s Glenfield valve and meet with current safety requirements. The existing valve actuator unit being water servo actuated from the penstock, whereas the new unit being failsafe twin oil actuated open and counterweight close. The new valve is capable of closing against a possible flowrate of 89cumecs within 55 seconds to protect the low-pressure tunnel and power station against any ruptures or incidents.

The primary obstacle that was faced during this project was the challenging access to the Portal Valve House, located above the power station. The Portal Valve house and ASCV were constructed and installed using a railway system which was subsequently removed following the commissioning of the Power Station in the 1950’s. The only access is now via a single lane forestry track with challenging gradients and several hair-pin turns.

After design review It was determined that a temporary lifting frame would be required, this was erected adjacent to the portal valve house to provide 15Te lifting capability to assist with both valve removal and installation. The next challenge was to provide transport for the old and new valves up and down the steep access track. After looking at various options, a Forestry Forwarder unit was chosen and retro-fitted with a bespoke transport frame suitable to carry and secure the large bore valve and its ancillaries. This also required the access road to be widened by approximately a metre to accommodate the turning radius of the vehicle.

Following successful removal of the ASCV, the pipeline was blasted and painted. The two 35” Anti-Vacuum valves underwent a full refurbishment at our Aberdeen based fitting facilities. A new 10” bypass pipework system was fabricated in stainless steel by AJT at our fabrication facilities and then installed, integrating a VAG guard valve and RIKO control valve which limits the fill rate of the Penstock.

Upon installation, the valve control was integrated to the stations PLC system. A new Pipe Rupture system was provided by Rittmeyer, Switzerland and installed by AJT. The Rittmeyer system was also integrated into the PLC to allow fully automated penstock rupture protection.

AJT would like to thank all the contractors that played a large part in making this job successful. Cadherent for the design work, drafting and site laser scans. Stoddart Crane Hire for all site craneage. Mcdonald scaffolding and IES for all electrical works.

Published: 28th January 2021