Watt steam engine

8 March 1776, at Bloomfield Colliery

In 1776 a full-size engine incorporating James Watt's separate condenser was set to work at Bloomfield Colliery near Tipton and Dudley — the first Boulton-and-Watt engine to operate commercially outside the Soho Manufactory.

The date comes from Aris's Birmingham Gazette of 11 March, which reported that the engine had started "Friday last", and is confirmed by specialist local histories.

The colliery's proprietors had abandoned a partly erected conventional engine to back Watt's unproven full-size design.

A fifty-inch cylinder at fifteen strokes a minute

John Wilkinson supplied the large iron foundry components, the specialized condenser, valve and piston work came from Soho, and Isaac Perrins erected the engine to Watt's plans and direction.

The 50-inch cylinder with its 7-foot stroke was three times the diameter of Watt's experimental engine and demanded unprecedented boring accuracy. At the public trial it ran at about 14 to 15 strokes a minute and cleared the pit's standing water in under an hour, after which the workers named it the "Parliament Engine."

Not exactly a sale

These engines were not complete machines sold from a factory. Customers funded construction while Boulton and Watt supplied plans, specialized parts, supervision and a patent licence, taking a royalty of one third of the coal-cost saving against an atmospheric engine.

The contemporary report claimed the engine used one quarter of the fuel a conventional engine needed for the same power.

Another early commercial Watt engine, blowing air for John Wilkinson's ironworks at Broseley, entered service around the same time — commonly dated to the following month.