Pump renovation project’s a Hull of an achievement

When AxFlow maintenance engineers were called in to restore the huge and historic drainage pumps at the East Hull pumping station, they were given a tight timeframe. But the challenging project was completed on target.

A challenge that AxFlow’s maintenance engineers face when called in to quote for a pump refurbishment project is not knowing what the condition of the internal components will be until the complete unit is stripped down. Externally the pumps may look to be either in a reasonable state or not worthy of being rescued. This was the situation that confronted AxFlow’s engineers when they were called in by Environment Agency (EA) contractor AMCO to the East Hull pumping station late last year. An external inspection in 2008 of the four Gwynnes 24” and 48” mixed-flow vertical land drainage pumps operating at the pumping station since 1949 indicated that the pumps were old and in need of replacement and had exceeded their design life capacity. When later removed from service by AxFlow for a thorough evaluation, it was clear they could be renovated to meet the EA’s future requirements. Most importantly, AxFlow would be able to undertake the renovation project in a timeframe quicker than a full replacement programme – and at a more competitive price. Hull is unusual because parts of the city are below sea-level when there is high tide and the plain around it is higher, meaning water from the Wolds tends to drain down towards the city. Therefore, it is important that there is a good, well maintained drainage system in the city. The purpose of the East Hull Works is to transfer water from the Holderness Drain into the River Humber over high tide periods. East Hull is the older of two pumping stations that service the city and both stations are currently undergoing a £16M upgrade to improve the capability to move sewage, surface water and land drainage out of Hull and into the River Humber. East Hull Works pumping station stands at the point where Holderness Drain flows into the Humber estuary and operates daily around high tide when the tidal gates on the Holderness Drain are closed. The four Gwynnes pumps are used to pump the drain into the estuary at times of high tide when the normal gravity discharge is prevented. In the past couple of years, the East Hull pumping station has been called into service more frequently so the EA, which has responsibility for the pumps, has implemented a £900,000 refurbishment programme in order maintain protection against flooding for 1,000 homes in East Hull. EA project manager Richard Hartley says: “The pumps needed an overhaul so we decided to do it alongside a major refurbishment being carried out by Yorkshire Water. We were looking at long-term options for the pumping station, but whatever we decided depended on the funding being available and any planning permissions. Meanwhile, we could not leave the Bransholme area unprotected so we decided to go ahead with a refurbishment, which buys us up to five years to review possible options.” AMCO was contracted to carry out the refurbishment and this involved a complete strip down and overhaul of the pumping equipment by pump maintenance specialist AxFlow. The EA also looked at how levels in the drain were controlled to maximise the efficiency of the existing pumping station. The existing building housing the East Hull Pumping Station was enlarged in 1972 to accommodate a sewage pumping system to carry screened effluent from the eastern side of Hull into the estuary. In 1989 overall responsibility for the site passed to Yorkshire Water, but the former National Rivers Authority took over maintenance of the four Holderness Drain pumps, passing to the EA in 1996. “In late 2009 we undertook an on-site evaluation of all four pumps in the East Hull works,” says AxFlow’s Mark Redgrove, “and made recommendations as to what work would need to be undertaken to put them all back into a reliable and efficient operating condition. In January, with assistance from AMCO, we removed the pumps and brought them to our Huddersfield works where we did a strip down to allow dimensional checks to be made along with a condition report.” The two 24” pumps, which were the first to be refurbished, were found to be in a reasonable condition, according to Redgrove. “We found that the bronze bushes, sleeves and grease-lubricated bearings were fairly well-worn but were serviceable, and the impellers had been repaired at some stage so there was no reason for additional work. The two 48” pumps did need more work and it was necessary to cast a new wear ring for the back of the impeller on the third pump as the original was cracked. “When the impeller race was removed on this pump it completely disintegrated. We found three new impeller races on site, so we were able to make use of one of these for this pump and also one for the fourth pump as it was necessary to cut the race to remove the impeller.” Looking at the refurbishment programme for all four pumps, AxFlow has balanced the impellers and replaced all of the wearing parts such as bushes and sleeves on the shafts. By their design, each of the pumps contain three or four shafts as the water flow from top to bottom of the sump is 7m, so the shafts are in sections. All the Michell bearings have been overhauled, the pads re-metalled, thrust collars skimmed and all the internal surfaces of the housing shot-blast and repainted. Running together, the refurbished pumps will a have the capacity handle 7.5m3/s and will be expected to run for periods of up to three hours at a time twice a day. “The key to the success of this contract was that we were able meet the EA’s request to work all four pumps at once, as opposed to instigating a rolling programme,” adds Redgrove. “Because of the size of these pumps, weighing up to 12 tonnes, it was necessary to dismantle them on site then rebuild them once the refurbishment jobs had been undertaken to check tolerance and dimensions. “We then had to dismantle them again for returning them to the pumping station and once again rebuild them on site. Because of the logistics of the programme of works on both the East and West works, we were given a tight timeframe. From first day onsite through to having the pumps re-installed and ready to run we were given 12-14 weeks.” www.axflow.co.uk

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