Post by jma1009 on Oct 11, 2015 10:35:33 GMT
i have spent far more time this year fiddling about with injectors than working on my 5"g terrier Stepney.
however it is something i enjoy doing even if at times my addled brain goes into meltdown sometimes.
the purpose of this thread is to share some of what ive learnt.
it is quite easy playing around with 'standard' designs. the sizes and details are all well known and published.
the problem occurs when replacing parts (damaged or wrong size) on non standard injectors as this requires a great deal of thought.
the Laurie Lawrence 'standard' design is based on the Keiller proportions, and used by commercial makers Ted Linden and copied legitimately by Arthur Grimmett after Ted's death. Derek Brown's 26 oz per min injector is based on the Laurie Lawrence design, as were John Cashmore's injectors. all of these are excellent and work very well. Laurie's articles also included a smaller injector in his standard length body called the 'weeny injector' designed by Bill Carter. Bill knew C.M. Keiller, Ted Linden , and Arthur Grimmett, all being SMEE members. Jim Ewins made his own injectors and was also part of this 'inner circle'.
Arthur was always a bit miffed that Laurie published in effect the details of his own commercial product without any acknowledgment. Arthur's main source of income was making them!
Don Young described a small injector for County Carlow with due acknowledgment to Arthur. it was carefully not a 'copy' and wont work well. he suggested altering it for Jersey Lily, but i cant see it would work any better!
by the time Don's 'Mountaineer was described in ME, his close friend Gordon Chiverton had started making injectors commercially. so as not to affect Arthur's business of making horizontal injectors, Gordon's were vertical injectors. it was immediately apparent that Gordon's injectors worked in a different manner. Gordon did not have the benefit of the Linden design details passed onto Arthur by Kennions, and so Gordon's achievement was quite remarkable.
in 1976 Basil Palmer described in ME the Eric Rowbottom small injectors. this series of articles showed why the LBSC designs could never be made to the required accuracy or work well (if you got one to work at all - which is generally acknowledged as 'luck'!). Laurie's first series on his 'standard' injector appeared the same year.
Arthur Grimmett stopped making his horizontal injectors around 1980, allowing Gordon to make horizontal injectors commercially. ownership of the Linden/Grimmet design details remained with Arthur for a few more years, so Gordon's horizontal injectors are the same re cone sizes and details as his vertical injectors.
the above all may sound totally irrelevant, but it isnt! when faced with a 'problem' injector the first thing is to establish what or upon what design it is based, and this determines how to proceed. it is those commercial makers who havent followed any of the above named gentleman that the real problems arise!
one other person deserves a mention - Roy Amesbury who described a rather special injector for his 'President' loco with adjustable steam cone. i knew this type well as Roy made one for Jack Thomas of the Cardiff (Whitchurch) club and was fitted to Jack's 5"g Brit. the steam cone setting was never altered, so Roy's added complication was not necessary.
traditionally, miniature injectors refer to number drill sizes for the cone 'throats' ie their smallest diameter. be very careful here! whilst there are batches of Number sizes a thou apart, there are gaps/big jumps in sizes and often these occur just when you want something in the middle! for example a 'standard' medium injector of 26 oz per min will have a steam cone throat of No.56 or No.57, and there is 3 and a half thou between these sizes! 65 and 66, and 70 and 71 also hve a 2 thou gap... you get the idea. to make a new steam cone for one of Gordon's 18 oz per min injectors i ream the taper till a 1mm drill will just go through. Gordon used a lot of metric sizes. a 1 thou difference to steam cone throat can make quite a difference to the operating range.
when using Derek Brown's tables for cone sizes (p.16 in his excellent book) it is worth noting that a lot of the successful commercial designs vary from this table, as does Derek's own 18 oz per min injector on p. 52.
generally err on the lower steam cone figure, and use the higher combining cone figure. all of Gordon's injectors have a first half of the combining cone of smaller proportion compared to the second half of the combining cone when compared to other makes, and also have a larger combining cone throat 'way off' Derek's table. there is no entry radius or chamfer on the start of the first half of the combining cone, neither does there appear to be the 'secret' Linden chamfer on the second half of the combining cone. the steam cone nozzle OD is also smaller, so the diverging nozzle length on same is shorter than that which Derek recommends. so already we have design parameters that depart from 'standard' yet work extremely well with a strong 'lifting' characteristic. marvel at Gordon's very clever checkvalve design (badly copied by others these days), but the real secrets are elsewhere!
reconstructing/ making a new steam cone to replace a damaged or worn or badly made steam cone is relatively easy and is fully described by Derek Brown. the annular gap set out on p. 64 is crucial and must be understood and adhered to. failure to do so is why many inferior commercial injectors fail to work at all or properly.
as an example i made a new steam cone yesterday for a well known inferior make where the steam cone nozzle was 20 thou too short and was too big internally (throat size too big). the old steam cone was also quite loose in the body.
a word on vertical injectors. i have explained above why they were specified by Don Young and made by Gordon Chiverton. LBSC also described one or two.
you cannot see if there is any muck or scale between the two halves of the combining cone, or between the combining cone and delivery cone. the delivery cone is pressed in and cannot be removed to clean the injector. very good filters are required and i would not advise their use in hard water areas.
cheers,
julian
however it is something i enjoy doing even if at times my addled brain goes into meltdown sometimes.
the purpose of this thread is to share some of what ive learnt.
it is quite easy playing around with 'standard' designs. the sizes and details are all well known and published.
the problem occurs when replacing parts (damaged or wrong size) on non standard injectors as this requires a great deal of thought.
the Laurie Lawrence 'standard' design is based on the Keiller proportions, and used by commercial makers Ted Linden and copied legitimately by Arthur Grimmett after Ted's death. Derek Brown's 26 oz per min injector is based on the Laurie Lawrence design, as were John Cashmore's injectors. all of these are excellent and work very well. Laurie's articles also included a smaller injector in his standard length body called the 'weeny injector' designed by Bill Carter. Bill knew C.M. Keiller, Ted Linden , and Arthur Grimmett, all being SMEE members. Jim Ewins made his own injectors and was also part of this 'inner circle'.
Arthur was always a bit miffed that Laurie published in effect the details of his own commercial product without any acknowledgment. Arthur's main source of income was making them!
Don Young described a small injector for County Carlow with due acknowledgment to Arthur. it was carefully not a 'copy' and wont work well. he suggested altering it for Jersey Lily, but i cant see it would work any better!
by the time Don's 'Mountaineer was described in ME, his close friend Gordon Chiverton had started making injectors commercially. so as not to affect Arthur's business of making horizontal injectors, Gordon's were vertical injectors. it was immediately apparent that Gordon's injectors worked in a different manner. Gordon did not have the benefit of the Linden design details passed onto Arthur by Kennions, and so Gordon's achievement was quite remarkable.
in 1976 Basil Palmer described in ME the Eric Rowbottom small injectors. this series of articles showed why the LBSC designs could never be made to the required accuracy or work well (if you got one to work at all - which is generally acknowledged as 'luck'!). Laurie's first series on his 'standard' injector appeared the same year.
Arthur Grimmett stopped making his horizontal injectors around 1980, allowing Gordon to make horizontal injectors commercially. ownership of the Linden/Grimmet design details remained with Arthur for a few more years, so Gordon's horizontal injectors are the same re cone sizes and details as his vertical injectors.
the above all may sound totally irrelevant, but it isnt! when faced with a 'problem' injector the first thing is to establish what or upon what design it is based, and this determines how to proceed. it is those commercial makers who havent followed any of the above named gentleman that the real problems arise!
one other person deserves a mention - Roy Amesbury who described a rather special injector for his 'President' loco with adjustable steam cone. i knew this type well as Roy made one for Jack Thomas of the Cardiff (Whitchurch) club and was fitted to Jack's 5"g Brit. the steam cone setting was never altered, so Roy's added complication was not necessary.
traditionally, miniature injectors refer to number drill sizes for the cone 'throats' ie their smallest diameter. be very careful here! whilst there are batches of Number sizes a thou apart, there are gaps/big jumps in sizes and often these occur just when you want something in the middle! for example a 'standard' medium injector of 26 oz per min will have a steam cone throat of No.56 or No.57, and there is 3 and a half thou between these sizes! 65 and 66, and 70 and 71 also hve a 2 thou gap... you get the idea. to make a new steam cone for one of Gordon's 18 oz per min injectors i ream the taper till a 1mm drill will just go through. Gordon used a lot of metric sizes. a 1 thou difference to steam cone throat can make quite a difference to the operating range.
when using Derek Brown's tables for cone sizes (p.16 in his excellent book) it is worth noting that a lot of the successful commercial designs vary from this table, as does Derek's own 18 oz per min injector on p. 52.
generally err on the lower steam cone figure, and use the higher combining cone figure. all of Gordon's injectors have a first half of the combining cone of smaller proportion compared to the second half of the combining cone when compared to other makes, and also have a larger combining cone throat 'way off' Derek's table. there is no entry radius or chamfer on the start of the first half of the combining cone, neither does there appear to be the 'secret' Linden chamfer on the second half of the combining cone. the steam cone nozzle OD is also smaller, so the diverging nozzle length on same is shorter than that which Derek recommends. so already we have design parameters that depart from 'standard' yet work extremely well with a strong 'lifting' characteristic. marvel at Gordon's very clever checkvalve design (badly copied by others these days), but the real secrets are elsewhere!
reconstructing/ making a new steam cone to replace a damaged or worn or badly made steam cone is relatively easy and is fully described by Derek Brown. the annular gap set out on p. 64 is crucial and must be understood and adhered to. failure to do so is why many inferior commercial injectors fail to work at all or properly.
as an example i made a new steam cone yesterday for a well known inferior make where the steam cone nozzle was 20 thou too short and was too big internally (throat size too big). the old steam cone was also quite loose in the body.
a word on vertical injectors. i have explained above why they were specified by Don Young and made by Gordon Chiverton. LBSC also described one or two.
you cannot see if there is any muck or scale between the two halves of the combining cone, or between the combining cone and delivery cone. the delivery cone is pressed in and cannot be removed to clean the injector. very good filters are required and i would not advise their use in hard water areas.
cheers,
julian
