From the very beginning providing an adequate water supply for the Regents Canal was a major concern. The summit level could be fairly easily maintained at the same depth as that in the Paddington arm of the Grand Junction Canal but, once locks were in use, all water supplied to the Regents would eventually cascade down to the Thames at Limehouse and be lost. There were ways in which this loss could be reduced. It was possible, in some places, to pump water back along the canal, although this would require expenditure on a steam engine. It would also be feasible to install double locks. These were two single chambers built side by side and connected with a conduit. When carefully managed this type of lock could speed traffic and save half a chamber of water each time they were used. When all four lock gates were closed, with one lock at each level and one or two boats in each lock, opening the conduit would allow water to run from the full lock to the empty one, raising boats travelling upstream whilst lowering those going the opposite way. Flow would stop when water was at the same height in each lock and, after closing the conduit, gate paddles could be used to control the respective water levels. However, taking the advice of James Morgan, the directors decided to try something more exotic. They would invest in an invention by William Congreve, a well regarded inventor, that promised almost minimal water loss.

Until becoming a baronet on the death of his father, who was the Comptroller of the Royal Laboratories at the  Royal Arsenal at Woolwich, William Congreve, was usually referred to as ‘Colonel’ Congreve. This was because he had been granted an honorary rank in the Hanoverian Army through his connections with the Prince Regent. Although not regular soldier Congreve certainly made an impact in the world of military rocketry for missiles which bore his name, developed from those captured in India during the Anglo-Mysore Wars of the late C18th, would be seen on European battlefields of the Napoleonic War and in the 1812 war against the United States too. The rockets were also used in naval warfare and for surveying purposes (see Chapter 7 in the Soochong, Shoguns and the Saracen’s surveys section of this website).

How the inventor came to be interested in the new link between Paddington and Limehouse is unclear. However, as an equerry to the Prince Regent and an acquaintance of John Nash he would have been well placed to follow developments and, aware that licences could be a lucrative source of income, went so far as to patent a technologically advanced ‘hydro-pneumatic double-balance lock’ that offered the promise of a huge reduction in water loss.

Congreve launched his invention, which would use compressed air rather than flowing water to raise traffic, with a small model. Having generated interest he then tried to overcome any scepticism about its operation by engaging Henry Maudslay, probably the best known manufacturer of precision machine tools in the country, to build a larger working model, to which the canal directors agreed to contribute £300. Once built this was inspected, according to Morgan, by some of the most eminent Scientific men in the country, and, he assured the directors, that I do not know of any objection having been made to it by them. Morgan was clearly very enthusiastic and asserted that from an economic point of view it would be well worthwhile using hydro-pneumatics to replace all the conventional locks. He pointed out that as each mechanical lock could accommodate a drop of more than 7 feet, only nine, instead of twelve conventional double locks, would be needed. Unfortunately, the cost of these nine locks, including Congreve’s licence fee of £250 per lock, would be over £50,000, which was more than twice the cost of all the standard locks originally planned. Nonetheless, Morgan thought the change would be worthwhile as the sale of redundant land previously bought for a reservoir at Finchley could help offset the extra expenditure. Moreover, no steam engine would be needed to pump up water from the Thames, which was another proposal to obtain an adequate water supply at the summit level. Even if Congreve’s locks did not reduce the loss of water completely, Morgan thought the ponds at Hampstead and Highgate could be acquired and these would more than compensate for any problems caused by leakage, seepage or evaporation. Water would reach the canal from these proposed supplementary reservoirs under the force of gravity.

Morgan’s support carried the day and it was agreed that, using components manufactured by Maudslay, a trial lock would be constructed at Hampstead Road to the general principles of the patent. When built it comprised of two chambers with a caisson in each, installed in-line rather than side-by-side as Congreve had originally intended. The two chambers were separated by a guillotine gate. Water in each chamber would be kept to a depth matching that in the canal. Below are the operational phases of the lock for a boat travelling from Paddington to Limehouse. Click  the thumbnail on the right for a simplified sketch of the lock showing the situation in the middle phase. It should be noted the lock also had a parallel motion system to ensure the caissons were kept level, but this is not shown.

Phase 1  A boat would enter the upper pound of the lock from the summit level (S on the sketch) through the upper guillotine gate, which was then closed behind it.

Before the boat began to be lowered a check would be made to ensure the lower guillotine gate, which separated the water in the lower pound from the water in the lower level of the canal (L on the sketch) was closed.

Both the boat and the water in the upper pound were supported by an inverted metal caisson held up by four hydraulic rams. These rams were installed at each corner of the space beneath the caisson. Four rams were also installed in the space beneath the lower caisson.


To lower the boat air was driven, via a hand operated pump in the lock house, from the upper pound rams into those serving the lower pound. Compressed air in the space beneath the upper caisson was also forced into the space below lower caisson

Phase 2  As the upper pound caisson sank, the lower pound caisson, and the water it supported, would rise. When both caissons were at the same level the middle guillotine gate would be opened to allow the boat to pass from the upper pound to the lower pound. The middle guillotine gate would then be closed. This is the point shown in the sketch.

Phase 3  The transfer of air would then be reversed and the upper caisson would rise as the lower one fell.  Once the lower caisson was at its lowest point the boat could pass through the lower guillotine gate into the lower level of the canal.

In Congreve’s view the operation of the lock pump would not be labour intensive and the transfer of a boat from one level to another would be speedy. Accordingly, the contract to build the lock, which was agreed between the canal company and Maudslay, stated; the lock shall pass their trade by the power of one man in three minutes without the loss of water.

It was anticipated that Congreve’s lock would be completed by October 1814 but work was delayed, not least because of the difficulty of making the caissons watertight. Not until July of 1815 was possible to authorise an official trial but this seems to have gone perfectly as far as the inventor and the constructor were concerned, which was clearly a relief to both of them. However, although the caissons had gone up and down as required and the guillotine gates had opened and shut on cue there were lingering doubts in the minds of some directors about how the lock would perform when in constant use. Could the air pressure in the rams really reach the required level with only one labourer manning the pump so it would actually be possible for a boat to pass from one level to another in only three minutes? More exhaustive trials were obviously required.

After more tribulation and demonstrations it was decided that a further trial would be held in August 1816 under the watchful eye of committee members and independent engineers, including Marc Brunel and Josias Jessop. Maudslay and Congreve must have looked forward to this event with some apprehension, because doubts about the effectiveness of the lock had been expressed by, amongst others, John Sutcliffe, a respected canal engineer, who was to write in his ‘Treatise on Canals’ (published in 1816) that Congreve’s locks;

possess more ingenuity than utility, for I am inclined to think the thread is too fine spun for general purposes; but if it would answer for that, the extraordinary expense of building added to that of taking care of it, would probably prevent it from being of public utility, but in this I shall be glad to find myself mistaken.

Sutcliffe’s estimates of the running costs of the locks would certainly have given many directors cause for concern. In his view a budget of £2000 per lock per annum would be necessary for maintenance, the employment of permanent mechanics would also be needed and should a breakdown occur there would be stoppage and a subsequent loss of toll revenue. Given these gloomy, but informed, views it would have been hardly surprising if some directors increasingly supported Sutcliffe’s view that; there will never be anything designed to equal a canal lock....for its simplicity, utility and durability.

No doubt Congreve, in response, would have made a strong case for how cost effective his locks would prove, perhaps not least because of the fees he would forgo if the proposed installation was abandoned. Fees generated by patent rights could be a lucrative source of income and interestingly, just at this moment, Congreve himself was involved in a dispute about a patent for a container that would keep gunpowder dry even when submerged. This challenge was linked to his position as Comptroller of the Royal Laboratories at the Royal Arsenal, a post he had held since the death of his father in 1814. In 1810 a Mr Walker had patented a kind of barrel to safely transport the ubiquitous explosive. When Walker discovered Congreve had authorised the production of similar barrels at Woolwich which were, in his view, an infringement of his patent, he sought an injunction, which was granted. Subsequently, when production did not cease, application was made to the Court of Chancellery to have Congreve committed to prison. Congreve’s defence was that he had not infringed the patent and, anyway, was a public servant doing his duty as the barrels had been produced for the armed forces. The Lord Chancellor accepted this view, dissolving the injunction instead. I doubt if anyone seriously expected Congreve to go to jail even if the injunction had not been dissolved and newspapers continued to carry items like this (also published in 1816) which boosted his prestige;  

Yesterday morning the Lords of the Admiralty with the two Secretaries, left town for Woolwich in order to witness experiment of new plan for Military Operations, devised by Sir William Congreve, who seems indefatigable in whatever tends in that respect to promote the public service

Despite concerns about the operation and maintenance costs preparations for the crucial August test of the hydro-pneumatic double-balance went ahead as planned. But, as everyone waited for it to begin and Morgan prepared to address Maudslay, Congreve stepped forward and presented a memorandum concerning the three minutes stipulated in the contract. Congreve wanted a liberal interpretation of the time taken and did not want the open and closing of the gates to be included. As Morgan did not agree Congreve said there was no point in running the trial and it was abandoned. Although the inventor still hoped to salvage something from the day, an attempt to show how efficient the lock was by running an unsupervised test in the afternoon did not succeed. Positive data about this unofficial test was passed to the General Committee of the canal company, but as it was not verified by Morgan it was not accepted. Moreover, in the afternoon test, compressed air vessels, rather than human labour at the pump, had been used to drive the rams.

Even had the hydro-pneumatic been built to Congreve’s original side-by-side specification, it is likely it would have been a disappointing failure as, from a technological point of view, it was probably too far ahead of its time. But the insistence by the canal company that the chambers be built inline made success even less likely and certainly reduced the possibility of transferring, within three minutes, a boat from one level of the canal to another. A further official test was scheduled for September 10th but opinion was running against the adoption of Congreve’s lock and neither this test nor any subsequent inspection or demonstration changed that.

One unfortunate consequence of the changing attitude was that relationships between the canal company and Maudslay soon deteriorated. The engineer certainly felt that even though he had done everything required to make Congreve’s lock function properly he was not treated fairly and the evidence seems to show he had a point. Matters dragged on acrimoniously through the period in which all work on the canal stopped due lack of funds but eventually the company decided to revert to ordinary double locks, pay Congreve a single licence fee and then sell the hydro-pneumatic for what the market would bear. There seems to have been no interest from any other canal company and as only scrap value was realised the whole project proved quite an expensive failure.

Congreve died in 1828 and the rights to his patents were put up for auction two years later. Thirteen lots were advertised, including one for a device which would assist in the ‘killing and rupturing of whales and other animals’. Another was for improvement in sluices and locks. Whether the hydro-pneumatic was included in this is not clear although as it was not advertised separately perhaps the patent had expired or, given the experience on the Regents, it was thought pointless to include it as there would be no bidders. To some extent the inventor’s reputation was tarnished towards the end of his life by unsavoury business dealings but his name was still a positive addition to any sales campaign. For example, an imported Maccasar Oil, which, so potential customers were assured, helped prevent baldness and imparted to the hair an imperishable quality and undecayed youthfulness was sold in bottles that had a label bearing an engraving from a design by Sir William Congreve. There seem to have been no end to his talents!

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When London Became An Island

Congreve’s Lock