21. These are simple poppet valves , operating by direct float action and sealing against the upper valve seat. 22. The rocket is fired when the computer sends direct current through a small electromagnet that opens the poppet valve . 23. Early designs used the D slide valve but this has been largely superseded by Piston valve or Poppet valve designs. 24. Use of poppet valves also increased the speed because they gave very accurately-timed steam delivery to the cylinders. 25. The poppet valves were not a great success and they all reverted to piston valve engines between 1931 and 1934. 26. The innovation trialled on # 5699 was its use of Caprotti valve gear, a poppet valve gear invented in Italy. 27. With no inlet pressure, the spring above the diaphragm pushes it down on the poppet valve , holding it open. 28. The ball lock valves may be unscrewed using wrenches to allow further cleaning or replacement of O-rings or poppet valves . 29. James Watt was using poppet valves to control the flow of steam into the cylinders of his beam engines in the 1770s. 30. Intake and exhaust poppet valves could be moved and controlled independently of each other, allowing for better control of the cycle.
