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Valve Chest

One of the important machinery features identified during the 2000 field season was the port engine's valve chest, the device that regulates the flow of steam into the main engine cylinder. Denbigh Project volunteer Gene Shimko, an engineer with considerable professional experience working with reciprocating engines, provided invaluable assistance in the identification and analysis of this particular feature of the wreck.

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This diagram shows a valve chest similar to Denbigh's, taken from a contemporary engineering textbook. The valve chest is a rectangular box atop the engine cylinder, the upper part of which is also shown. The view here is looking from the right side of the ship; the bow would be toward the right of the picture. "Live" steam, piped into the valve chest directly from the boiler, is shown here in bright red.

There are two valves in the chest, a Cutoff (or Expansion) Valve and the Main Slide Valve. The main slide valve assembly sits directly on top of the cylinder and slides on a machined face. The cutoff valve consists of two blocks connected by a double reverse screw. The cutoff valve slides within the main slide valve assembly, sitting directly on the top of the main slide valve ports. In effect, the Cutoff Valve regulates live steam to the Main Valve ports, which in turn passes it into alternate ends of the engine cylinder, pushing the piston back and forth. At the same time, the spent steam from the previous stroke (black) is exhausted out of the cylinder to the condenser, where it will be converted back to liquid water and returned to the boiler.

Click here for a 113kb GIF image showing this animation frame-by-frame.

The Cutoff and Main Valves are themselves powered by the rotating paddlewheel shaft via eccentrics, so that once set in motion the whole assembly should continue to operate as long as sufficient steam is provided. The precise timing of the Cutoff Valve could be adjusted by the threaded rod shown running through its center; this could be used to make the engine operate more efficiently. Denbigh's engine was considered "double acting" because steam pushed the piston both forward and backward.

Valve chest illustration from William S. Auchincloss, Practical Application of the Slide Valve and Link Motion (New York: 1869).


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What's New?

new.gif (977 bytes) John Newland Maffitt and the Galveston Blockade | Chasing a Fox new.gif (977 bytes)
new.gif (977 bytes) 2001 Field Crew | In-Kind Contributions  | How Much Coal? new.gif (977 bytes)
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"An Extremely Fast Boat" | The "Mobile Packet" | A "Bold Rascal" | Denbigh Today
Denbigh's Crew | The Erlanger Loan | Birkenhead-Built: An Unrivaled Legacy
Denbigh Primary Source Documents | Galveston During the Civil War | Denbigh, Clwyd, Wales
The U.S. Coast Survey and the Blockade, 1861 | The Ship's Library: Recommended Reading
Running the Blockade Into Galveston: A Personal Narrative | Denbigh Day-by-Day
Denbigh Portrait | Official Number 28,647 | Valve Chest Animation (300kb) | Investors
Links of Interest | Denbigh F.A.Q. | Denbigh's Engines | Denbigh's Boiler
Feathering Sidewheel


April 27-28 Side Scan Survey | May 7-10 Site Mapping
June 16-17 Sub-Bottom Profiling | Site Mapping, July 9-12, 1998 | Dive Trip, October 18-30, 1998
Underwater Images | 1999 Summer Field Season | Denbigh Site Plan
Jerry Williams Speaking Tour | Denbigh Project Benefit Dinner |
Denbigh Artifacts | 2000 Field Crew | 2000 Field Crew Photo Album |
The Denbigh Wreck Site: A Quicktime VR Panaorama
Connecting Rod Recovery, July 22-24, 2000 | Modeling a Shipwreck
Credits & Thank-Yous

J. Barto Arnold et al. 1998-2000, The Denbigh Project, World Wide Web,
Institute of Nautical Archaeology, Texas A&M University, E-mail: (  
Sunday, July 16, 2000 Revision.

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