Query: How many barrels did Lofting promise his beer pump would deliver hourly?
Context: "Whereas their Majesties have been Graciously Pleased to grant Letters patent to John Lofting of London Merchant for a New Invented Engine for Extinguishing Fires which said Engine have found every great encouragement. The said Patentee hath also projected a Very Useful Engine for starting of beer and other liquors which will deliver from 20 to 30 barrels an hour which are completely fixed with Brass Joints and Screws at Reasonable Rates. Any Person that hath occasion for the said Engines may apply themselves to the Patentee at his house near St Thomas Apostle London or to Mr. Nicholas Wall at the Workshoppe near Saddlers Wells at Islington or to Mr. William Tillcar, Turner, his agent at his house in Woodtree next door to the Sun Tavern London."