Savery also worked for the Sick and Hurt Commissioners, contracting the supply of medicines to the Navy Stock Company, which was connected with the Society of Apothecaries. His duties on their behalf took him to Dartmouth, which is probably how he came into contact with Thomas Newcomen.
Savery's engine had no piston, and no moving parts except from the taps. It was operated by first raising steam in the boiler; the steam was then admitted to the working vessel, allowing it to blow out through a downpipe into the water that was to be raised. When the system was hot and therefore full of steam the tap between the boiler and the working vessel was shut, and if necessary the outside of the vessel was cooled. This made the steam inside it condense, creating a partial vacuum, and atmospheric pressure pushed water up the downpipe until the vessel was full. At this point the tap below the vessel was closed, and the tap between it and the up-pipe opened, and more steam was admitted from the boiler. As the steam pressure built up, it forced the water from the vessel up the up-pipe to the top of the mine.
Savery took great care to stress how powerful his engine was, and was the first to use the term "horsepower". However, his engine had three serious problems. First, every time water was admitted to the working vessel much of the heat was wasted in warming up the water that was being pumped. Secondly, the second stage of the process required high-pressure steam to force the water up, and the engine's soldered joints were barely capable of withstanding high pressure steam and needed frequent repair. Thirdly, the engine could only raise water about and as a result had to be installed far down in a mine, and a deep mine would need a series of engines to raise water all the way to the top.
Savery's patent covered all engines that raised water by fire and Newcomen was forced to go into partnership with Savery. By 1712, arrangements had been made with Newcomen to develop Newcomen's more advanced design of steam engine, which was marketed under Savery's patent. Newcomen's engine worked purely by atmospheric pressure, thereby avoiding the dangers of high-pressure steam, and used the piston concept invented in 1690 by the Frenchman Denis Papin to produce the first steam engine capable of raising water from deep mines.
After his death in 1715 Savery's patent and Act of Parliament became vested in a company, The Proprietors of the Invention for Raising Water by Fire. This company issued licences to others for the building and operation of Newcomen engines, charging as much as £420 per year patent royalties for the construction of engines. In one case a colliery paid the Proprietors £200 per year and half their net profits "in return for their services in keeping the engine going".
The Fire Engine Act did not expire until 1733, four years after the death of Newcomen.
One of his engines was set up at York Buildings in London. According to later descriptions this produced steam 'eight or ten times stronger then common air' (i.e. 8-10 atmospheres), but blew open the joints of the machine, forcing him to solder the joints with spelter.
A few Savery engines were tried in mines, an unsuccessful attempt being made to use one to clear water from a pool called Broad Waters in Wednesbury (then in Staffordshire) and nearby coal mines. This had been covered by a sudden eruption of water some years before. However the engine could not be 'brought to answer'. The quantity of steam rasied was so great as 'rent the whole machine to pieces'. The engine was laid aside, and the scheme for rasing water was dropped as impracticable. This may have been in about 1705.
Another engine was proposed in 1706 by George Sparrow at Newbold near Chesterfield, where a landowner was having difficulty in obtaining the consent of his neighbours for a sough to drain his coal. Nothing came of this, perhaps due to the explosion of the Broad Waters engine.