This , in effect , slid backwards and forwards admitting steam to one end of the cylinder then the other .
In 1799 William Murdoch , who worked for the firm of Boulton and Watt , invented a new type of steam valve , called the D slide valve .
In effect , slid backwards and forwards admitting steam to one end of the cylinder then the other .
In 1799 William Murdoch , who worked for the firm of Boulton and Watt , invented a new type of steam valve , called the D slide valve .