Expansion valve (steam engine)
An expansion valve is a device in
An expansion valve is a secondary valve within a steam engine. They represent an intermediate step between steam engines with non-expansive working and later valve gears that could provide for expansion by controlling the motion of a single valve.
Expansion valves were used for stationary engines and marine engines.[1] They were not used for locomotives, although expansive working was achieved by the use of the later variable expansion valve gears.
Need for varying expansion
The pressure of the expanded steam is less than that of steam supplied directly from the boiler. An engine working with an expansion valve set to an early cut-off is thus less powerful than with the valve fully open. Accordingly, the engine must now be driven, so that the valve is manually adjusted as the load on the engine changes. An engine running under light load may be operated efficiently with an early cut-off, an engine under heavy load may require a longer cut-off and the cost of more steam consumption.
When
Gridiron expansion valves
The gridiron valve[5] was one of the first forms of expansion valve.[1] The gridiron valve is an arrangement of two plates with overlapping slats. One plate can move so that its slats overlap either the slats of the other plate, or the slots between them, to thus be either open or closed. It has the advantages of a relatively large opening (up to half of the total area) and a rapid opening, needing to be moved by only one slat width to change from fully open to fully closed. Its disadvantage is that they do not seal particularly well. Because of the short actuating distance for a gridiron valve their valve timing would be relatively imprecise if used with an eccentric or similar. Some large steam engines later used them as primary valves, either as exhaust valves for LP cylinders[6] or as inlet valves in conjunction with trip-[7] or cam valve gear.[8][iii]
Where gridiron valves are used as secondary valves, they were commonly mounted on the inlet side of the valve chamber for the primary slide valve. They were driven by a separate valve gear, usually a separate eccentric set in advance of the main eccentric.[1] When operating, the additional advance moves the gridiron valve to apply cut-off ahead of the main valve. To vary the expansion they provide, the stroke of the eccentric drive can be varied by an adjustable linkage. When this is adjusted to zero throw, the expansion valve remains fully open and the engine works without expansion.[1] Although the use of a secondary gridiron valve was an early technique, it also remained in service with increasingly sophisticated valves and actuation, throughout the history of stationary engines. McIntosh and Seymour engines used one driven by a cam and toggle arrangement that moved intermittently and stood still when open, giving precise timing, and independent adjustment of each valve movement.[9]
Gridiron valves were also used on the backs of slide valves, in the manner of the Meyer valve.[7] This was a patent of John Turnbull of Glasgow in 1869.[10]
Meyer expansion valve
The best-known design of expansion valve was the Meyer, the invention of French engineer Jean-Jacques Meyer (1804-1877) who applied for a patent on 20 October 1841. A similar valve was patented by James Morris.[11] A second slide valve rides on the back of an adapted main slide valve and is driven by an additional eccentric. In the Meyer valve, the effective length of the expansion valve[iv] can be altered with a handwheel whilst the engine is running. The valve has two heads mounted on left- and right-handed threads on the handwheel's valve rod, so that rotating the wheel moves the heads either together or apart.[12][13] In this arrangement the cut-off is normally controlled manually. Although automatic control was attempted, it was too slow-acting to be effective.
Engines on display at
Compound engines
Expansion valves were also fitted to compound steam engines. Both techniques are an attempt to achieve greater efficiency, even at the cost of more complexity.
It was usual for expansion valves to be fitted only to the HP (high-pressure) cylinder. Steam supplied to the following LP (low-pressure) cylinder has already been supplied to the engine, so there is little benefit to conserving it. Any early cut-off of the steam inlet to an LP cylinder may also represent throttling the exhaust of the preceding HP cylinder, and a reduction in the efficiency of that cylinder.
Later compound
Link valve gears
Developments after the separate expansion valve led to more sophisticated valve gears that could achieve the same goal of varying
Automatic governors
'Automatic' engines, and in turn high-speed engines, operated at increasing speeds and required more precise control of their speed under varying load. This required the coupling of their governor to the expansion valve gear. Earlier engines with Watt's centrifugal governor and throttle valve become inefficient when operating at low power.
The Richardson governor
Successor valve types
In the fully developed forms of the high-speed engine (from around 1900) though, expansion was controlled by governing the timing[v] of a single valve, rather than a separate expansion valve. These led to further complex valve types such as poppet valves, often driven by cam-based valve gears rather than linkages.[vi]
Increasing use of superheating encouraged the replacement of slide valves with piston valves, as these were easier to lubricate at the increased operating temperatures. They also made it impractical to use secondary valves like the Meyer, running on the backs of the primary valves. Possibly the last new design to use a secondary valve as an expansion valve was the Midland Railway Paget locomotive, that used bronze sleeves as expansion valves around its cast iron rotary valves.[20] This design was unsuccessful, owing to mechanical problems with differential thermal expansion of the two valve materials.[21]
Expansion Valve Market in the world
The AC expansion valve market is highly competitive and consists of several major players. Some of the key players in the market include Fujikoki, SANHUA Automotive, Valeo, Denso, Hanon Systems, Mahle, Keihin, Eberspacher, Mitsubishi Heavy Industries, Subros, Sanden Holdings, and Calsonic Kansei.[22]
Fujikoki is a prominent company operating in the Automotive Electronic Expansion Valve (EEV) market. Since its founding in 1953, Fujikoki has made a name for itself as a leading supplier of automotive thermal management products worldwide. The business specializes in the manufacturing of valves and related products for various applications, including automotive air conditioning, residential air conditioning, commercial applications, and ecological equipment
Valeo is another major player in the AC expansion valve market. The company specializes in automotive technology and produces a variety of AC systems, including expansion valves. Valeo has a strong global presence and a wide customer base.
Denso is a renowned global company that provides automotive components, including AC expansion valves. The company has a long history dating back to 1949 and has become one of the leading suppliers in the automotive industry.
Hanon Systems is a multinational company that specializes in climate and thermal management products for the automotive industry. They provide a wide range of AC expansion valves and have a strong presence in the market.
Mahle is a leading global supplier of automotive components and systems. They offer a variety of AC expansion valves and have a strong focus on research and development to continuously improve their products.
Footnotes
- ^ This fall of pressure with expansion is inevitable, according to Boyle's law.[2]
- ^ This engine was one of the first to employ any cut-off and deliberate expansion of steam. However this cut-off was fixed and could not be varied whilst the engine was working.
- desmodromic cam-driven valve gear with very fast-acting gridiron valves driven at half crankshaft speed was a key feature of Ferranti's high-speed cross compound vertical generating engines.[8]
- inlet lapof the valve.
- ^ As this was the timing of the valve that was controlled, not its stroke, it avoided some of the Stephenson link's throttling drawback.
- ^ Link and radius valve gears are simple to make but have performance limitations. Arbitrarily-shaped cams can offer valve control tailored closer to an ideal operation, although they were difficult to manufacture accurately and their performance worsened dramatically as they wore. Improvements to machining techniques, metallurgy and lubrication increasingly favoured the cams.
References
- ^ a b c d e Evers, Henry (1875). Steam and the Steam Engine: Land and Marine. Glasgow: Williams Collins. pp. 78–81.
- ^ a b c Evers (1875), pp. 51–53.
- ^ Hills 1989, p. 102
- ^ Trevithick, Francis (1872). Life of Richard Trevithick with an Account of his Inventions. Vol. II. p. 132.
- ^ Evers (1875), pp. 73–74.
- ^ Southworth (1986), p. 26
- ^ a b Hills 1989, p. 188
- ^ a b Hills 1989, pp. 226–227
- ^ Hawkins, Nehemiah (1897). New Catechism of the Steam Engine. New York: Theo Audel. pp. 97–99.
- ^ GB 3207, published 1869-11-05
- ^ GB 9571, James Morris, published 1842-12-22
- ISBN 0-9511856-0-8.
- ^ "The expansion slide valve and governors". Old Engine House. Archived from the original on 2012-02-04. Retrieved 2012-03-30.
- ISBN 0-521-45834-X.
- ^ Robey & Co. engine of 1887 Southworth (1986), pp. 21–22, 24
- ^ Evers (1875), p. 78
- ^ GB 14753, John Richardson, published 1885
- ^ "The Richardson Governor". Old Engine House. Archived from the original on 2011-09-19. Retrieved 2012-03-30.
- ^ Southworth (1986), p. 20
- Ahrons, E.L. (1966). The British Steam Railway Locomotive. Vol. I, to 1925. Ian Allan. p. 345.
- ^ Self, Douglas (8 February 2004). "The Paget Locomotive". Loco Loco gallery.
- ^ Critical Reports. "Automotive Electronic Expansion Valve Market Research Report Provides thorough Industry Overview, which offers an In-Depth Analysis of Product Trends".