HILLMORTON DUPLICATE LOCKS
In 1769 an Act of Parliament authorising the Oxford Canal was promoted by Oxford Canal Company Chairman, Sir Roger Newdigate MP, to link the industrial English Midlands to London via the River Thames. James Brindley supervised the surveying of the route and initial construction, assisted by his brother-in-law Samuel Simcock.
Hillmorton, (or at that time ‘Hilton’ on the hill and ‘Morton’ on the moorland below) required a flight of three single locks to give a total lift of nearly 19 feet. The first building phase from Coventry started immediately along with work on the locks, which proved lengthy. Shifting sand had to be overcome by sinking wooden rafts on which to build, and powerful pumping had to be devised and installed to restore the water used, to the top.
A windmill was originally pro-posed as the motive power for a water pump, but the choice was a stately beam engine, of the usual gargantuan proportions. Capable of lifting water the required 18ft l0 ¼ inches, its cylin-der was over 2 foot in diameter, with a stroke of 6½ft, and it delivered a leisurely 12 strokes per minute. Fuel consumption was l½cwt of coal for just over 4 locks of water.
Before Morton Flight was completed, James Brindley died in 1772 (the locks approach road was named Brindley Road). Samuel Simcock took over and completed the Morton Flight, but did not reach Napton until 1774 and the Company was now out of money.
So the Brindley designed canal did not reach Oxford until 1790. However, it did then generate the anticipated volume of through traf-fic with substantial profit. It was not to last, and by 1829 business was in serious de-cline, with increasing competi-tion from the Grand Junction Canal, plus a major new threat from the railway. Immediate action was essential. A hurriedly put together survival plan was formulated to drastically straigh-ten and shorten the northern end of the expensively me-andering contour canal.
lssambard Kingdom Brunel undertook the initial survey, with Charles Vignoles handling detail planning. The terrain of the new route would inevitably involve tunneling, deep cuttings, huge embankments and aqueducts. (One short cut left a redundant and blocked off arm below the locks at Hillmorton and this was eventually utilised as a Basin for the canal company HQ andis now the subject of restoration.)
Despite the huge amount of work, the task was completed without serious delay and was re-opened on 13th February (some say May)1834, but there was a price to pay. The original aim to shorten the canal by 14miles at an esti-mated cost of £131,877 became 11miles and the final bill of precisely £167,172.27d. A modest overspend by to-day’s standards, and it proved to be a sound investment - but with a sting in the tail! The traffic flow increased to the extent that within six years there was a persistent bottleneck at Hillmorton, which then still had only the three single locks with boats queuing to go through. Time was money to working narrow boats, and lost profit for the company. Improved passage was vital.
The bottleneck problem could have been foreseen, and steps taken to widen the locks and/or duplicate them at the time of the canal shortening work, particularly as the lower lock was relocated at that time. However, better late than never, in 1840 it was agreed to duplicate the Morton Flight, complete with integral side ponding.
The ‘Duplicate Locks’ were a crucial survival factor for the Oxford Canal. A dictionary definition of ‘duplicate’ is an exact copy of the original, but in fact the lock chambers are not exact brick by brick replicas. Apart from an obvious advantage, duplicate locks can also provide a hidden water saving asset. The twin locks are built side by side, though not always at the same time - or in precise alignment. At Hillmorton, the second lock of each pair was added later. The cost was obviously much greater than single lock flights - probably well over double! Canal owners were not too well known for their desire to spend money. So why did the Oxford Canal Company make such an expensive investment?
The purpose of side pond-ing is to stop valuable water being flushed downhill in vast quantities. Brickwalled basins are built alongside the ap-propriate lock or locks. Water discharged from an emptying lock goes into the side pond, where it is held, to be returned to the lock when it is being filled for an upward passage. About half a lockfull of water is saved at each pass. Duplicate locks were a deve-lopment of side ponds, inven-ted, it is said, by James Morgan, who first used them on the Regent’s Canal. One flight of locks was used for ascending craft and the other for those descending - thus one lock served as the side pond for the other. Although the saving could never be more than half a lock of water, as when the locks were half full they would balance out, it was an effective solution.
The enlightened decision to duplicate achieved the double benefits of relieving the bottleneck, and saving precious water. Keeping pace with technology, a somewhat smaller, but still impressive steam engine and centrifugal pump were installed. The work was completed on 15th August 1840 and opened to the trade on 25th August.
The new system was efficient, it was possible for a boat to pass through each lock, even using the additional side pond-ing paddle in just 80 seconds! The lock chambers were designed to fill in a staggering 29 seconds, and soon an impressive average of 400 working narrow boats a week were passing through the new locks. The Oxford Canal was to remain well in profit until the 20th century.
Steam power eventually gave way to oil with a 32bhp paraffin engine, which powered the same l3in belt driven cen-trifugal pump. Sadly these pre-cious heritage items have been lost. Oil in turn was superseded by elec-tricity, which now drives the pumps on the tow-ing path side. The switch gear and meter are in the little white hut by the bottom lock, usually mistaken for an old toll house but actually the duty lock keeper’s lobby (Today’s Volunteer Lock Keepers may note).
Sources of information and passages in this document
Tony Miles, Coventry Waterways Scheme 1995
F.Wood, Parish Rate Assessment 1852
John Chatham Canal&Riverboat magazine March 1994