Elta Supply Ventilation Fans for the A3 Hindhead Tunnel

Elta have supplied specialist fans for the road tunnel being built as part of a new bypass for the A3 in Surrey. The trunk road is the major highway between London and Portsmouth on England’s south coast, previously climbing around the side of the Devil’s Punch Bowl, the large natural amphitheatre, landmark and beauty spot near the village of Hindhead.

It is a Site of Special Scientific Interest and designated part of a Special Protection Area. The new tunnel, which is a total of 1.2 miles long, is the longest non-estuarial tunnel in the United Kingdom. The maximum depth below ground, measured to the top of the tunnel, is about 200ft.

A full technical submittal on Elta Building Services Division proposals was required by ventilation contractors, James Paget Services, along with a formal letter of life expectancy for the units. Orders for the specially manufactured units, were then placed in April and May 2010. The first part of the order comprised two sets of long-cased, axial ‘run & standby’ fans with matching stainless steel ancillaries for ventilation of the void in the low-point sump.

After Elta sought confirmation from the motor supplier that it was possible to do so, each fan is set to work for 12 hours then switch to standby mode. They then operate in the opposite direction, switching again after each 24-hour period. “Windmilling” losses for standby fans, along with the control logistics of forward/reverse operation were decisive factors in the model selection process.

The second part of the order was for four bifurcated, cylindrically cased ATEX axial fans with matching ancillaries. Manufactured by the Fareham based Applied Technology Division of Elta these were designed to meet specific site requirements when supplying air and extracting gases from the drainage impounding sump. The bifurcated fans are quality, direct motor driven units, specially developed for handling hostile conditions of hot, dust-laden air, corrosive fumes or gases. The units are designed so that the gases by-pass the motor in order to eliminate any detrimental effects.

Two temperature options are available in either a cylindrical or conical casing. Elta manufactures a range of fans to meet the European Union (EU) directive ATEX (ATmosphÌÄå¬res EXplosibles) which coordinates various technical and legal conditions throughout Europe. This new and evolving standard ensures safety of equipment installed and operated in potentially dangerous atmospheres by reducing the explosion risk through established design methods.

The new, twin-bored road tunnel is an important part of the £371 million Hindhead project, one of the major schemes in the current Government’s programme of road works. The tunnel is part of the 4 milelong dual-carriageway currently under construction to replace the last remaining stretch of singlecarriageway. It will complete the 68 mile link between Portsmouth and the capital, removing a major source of congestion on a busy route (which carries over 28,000 vehicles per day) and improving road safety as well as air quality in the area. Work on the main tunneling works started in February 2008.

The tunnel features cross-passages every 100 metres along with state-of-the-art safety and communications systems. Secretary of State for Transport, Mr. Philip Hammond opened the Southbound bore to traffic on Wednesday, 27th July 2011, the first vehicles being escorted through the tunnel in convoy. Northbound traffic was introduced to the new road a few days later. It was opened within budget and on schedule.

Elta is part of the £85 million Elta Group, a family of businesses with operations in six countries on four continents which, together with a network of international distributors, provides quality fans and related air movement equipment to customers worldwide.