- Was this conversion by Lima in 1939 the only one? 2. Were others modernized by PRR itself. 3. How does a front-end throttle improve performance?
One advantage of a front-end throttle is that it reduces the response time of the locomotive to throttle changes.
No other K4 got rebuilt the way 5399 did. One or two others got poppet valves.
What Type popet-valves were used?
5399 was fitted with Franklin Type A valve gear.
This conversion is dealt with in detail in Vernon L Smith’s “One Man’s Locomotives”.
The conversion to a front end throttle was part of a conversion to increase the steam flow area right through from the boiler to match the capability of the poppet valves. This involved changing the dry pipe, the throttle and the superheater. 5399 originally ran with the poppet valves and the original boiler and throttle, but was modified to increase its power. It could haul a train normally requiring two standard K4 locomotives.
Peter
On 5399, the Franklin System type A with oscillating-cam drive was used: this has two small admission valves and two larger exhaust valves per cylinder end (this is the layout on the ‘heraldic shield’ in contemporary Franklin advertising!) This is the system adopted for the T1 construction, and in the rotary-valve T1 conversion (which used bridges to activate the paired valves from a single follower).
Oscillating cam poppet valves are something of a scam, because when operated from traditional valve gear the valve lift can be proportional to cam excursion, which is NOT productive of clean limited cutoff. (This is not necessarily a ‘bad’ effect when running at lower speed, for the same reasons the ‘type D’ in the Vulcan conversions for Army 2-8-0s were). It is interesting that the poppet-valve conversion was done before the large sine-wave superheater was put in.
3847, which was converted in 1945, uses a rotary-cam system, with the older very heavy Franklin outside drive frame similar to that on the C&O L-2 Hudsons with RC. That engine’s appearance can be studied here:
http://www.northeast.railfan.net/images/prr3847.jpg
In some ways this is a superior method, but only if fitted with continuous-contour cams (which are expensive to machine and difficult to maintain). Most of the RC systems with discrete cam profiles (e.g. British Caprotti and some Reidinger) tended to have poor performance off the regime for which the cams were machined – which was fairly often. It might be interesting to see if modern hard coatings can solve some of the issues with spherical followers running on continuous-contour surfaces at the speeds and pressures involved with the heavier progressive spring pressures in practical ‘debounced’ Franklin-style poppet valves.
The Hagley Museum and Trust has several PRR negatives of the 5399 in their collection.
From the captions it would appear the testing was done in Fort Wayne.
Good Luck, Ed
[quote user=“Overmod”]
daveklepper
What Type poppet-valves were used?
On 5399, the Franklin System type A with oscillating-cam drive was used: this has two small admission valves and two larger exhaust valves per cylinder end (this is the layout on the ‘heraldic shield’ in contemporary Franklin advertising!) This is the system adopted for the T1 construction, and in the rotary-valve T1 conversion (which used bridges to activate the paired valves from a single follower).
Oscillating cam poppet valves are something of a scam, because when operated from traditional valve gear the valve lift can be proportional to cam excursion, which is NOT productive of clean limited cutoff. (This is not necessarily a ‘bad’ effect when running at lower speed, for the same reasons the ‘type D’ in the Vulcan conversions for Army 2-8-0s were). It is interesting that the poppet-valve conversion was done before the large sine-wave superheater was put in.
3847, which was converted in 1945, uses a rotary-cam system, with the older very heavy Franklin outside drive frame similar to that on the C&O L-2 Hudsons with RC. That engine’s appearance can be studied here:
http://www.northeast.railfan.net/images/prr3847.jpg
In some ways this is a superior method, but only if fitted with continuous-contour cams (which are expensive to machine and difficult to maintain). Most of the RC systems with discrete cam profiles (e.g. British Caprotti and some Reidinger) tended to have poor performance off the regime for which the cams were machined – which was fairly often. It might be interesting to see if modern hard coatings can solve some of the issues with
This was essentially the same design adopted for the T1 (remembering that one side was driven from the opposite crosshead, a design I believe Wil Woodard had a hand in developing), What you forget is that the crosshead drive did not move the cams directly: there are two additional pieces of equipment in there. One of these in essence contained a stunted little set of link valve gear, which is what imparted the swing to the oscillating cams. There have been subsequent plans to give more of a ‘Corliss’ effect to the poppet-valve excursion (a couple being to use a mechanism tripped by valve gear position to move the valve desmodromically, analogous to the spring action that physically moves the Corliss valve from lock to lock). At least in principle this gets around some of the shrouding that results from very short cutoff, but introduces some problems of wear and inertial effect of its own.
RC gear, of course, has neither a substantial shrouding of valve openings or a periodic reversal of momentum of the cam to accommodate.
Why were not more K4s improved? It would seem like reduction in crew costs would have made the investment worthwhile. Or were savings eaten up in additional maintenance costs?
How did these improved K4s compare with the two K5s?
What you forget is that the crosshead drive did not move the cams directly: there are two additional pieces of equipment in there.
I didn’t forget it. I checked the drive from one of the photos in the Hagley group linked earlier.
This is in principle the same drive as the Young gear used on the UP 7000 4-8-2, which was replaced by Walschearts gear, most memorably on the streamlined 7002. Whatever the theoretical disadvantages, 5399 actually worked rather well. It had the advantage that the gear was readily accessible in that application. Smith commented that the subsequent application on the T1s resulted in poor accessibility, not only in the rear cylinders, but due to the streamlined boiler casing extending over the forward gear.
As Dave no doubt recalls, one of the K5s had Caprotti gear which did not show the advantages that 5399 demonstrated.
Peter
This goes to show the evils of assumption, where references talk about the crosshead drive being similar, and I look at photos just enough to conclude the crosshead was driving mechanical lubrication. Upon review I believe this is the system shown in Woodard’s patent 2234614 of March 11, 1941.
This raises something else interesting: the substantial cylindrical device on the lower rear cylinder head visible in the picture. I don’t know if this is a typical compression-relief device but it is considerably longer than any I (admittedly, again, not very carefully) have seen in late practice. Good secondary compression relief (and I agree with Jay Carter that having it reversible, like an extension of ‘cushioning’ compression volume in the endspace up to the valves, would be a great advantage.
Interestingly, the nightmare-box part of the T1 gear (the thing that was on end and crammed between cylinders for the rear engine) was apparently not the thing that needed serious maintenance attention – it could be sealed and given oil changes and according to a couple of notes in the T1 Trust engineering committee discussions very few of them seem to have required working on. It was the other piece, the little radial gear in a box, that seems to have been involved in many problems. I don’t remember any definitive answer on how much of this was related to increasing the spring pressure to ‘debounce’ the poppet valves. (Better control of the valves was one of the projects for 1948 that were not ‘proceeded with’.)
The Caprotti gear was on there largely because Baldwin made an agreement in the late '20s, thinking Caprotti poppet-valve gear was going to be the wave of the future, and succeeded in flogging it to a large number of railroads. They even featured logging and narrow-gauge export locomotives with it. To my knowledge it was successful nowhere Baldwin tried it, and eventually had to be removed; to my kno
I agree that a modernized M-1 fleet would have been a better investment than just about anything in steam PRR could have done, T-1s. Q-2s, or even modernized K4s.
By the way-- those are test-plant results. PRR said in the 1939 road tests, before the boiler improvements, 5399 did 2800 dbhp at 80 mph, compared to 2000 for a standard K4.
Franklin rotary poppet [valve] gear drive, possibly located on #1 axle.
Poppet_drive by Edmund, on Flickr
PRR 5399. PRR Photo E12275, Hagley Trust. According to their file.
This view better illustrates the levers that communicated the cam box with the combination lever as discussed above:
Regards, Ed
I think the rotary drive on the locomotive axle would be for a lubricating oil pump. Vernon Smith, who was involved in the design of the gear on 5399, says “the cams to operate (the poppet valves) were placed in a double deck cam box that required an oil pump to lubricate the upper cam and rollers”.
He also said “since the drive for the gears came from the locomotive crossheads only, it was neccesary to cross the drive over inside the box to get the motion in the correct phase to drive the respective links.”
Peter
I believe that is a necessity for any crosshead drive, going back to the earliest examples which are I believe in British practice.
See also the Berry accelerator gear (on Dr. Richard Leonard’s site) for a different application of the principle.
I must be getting my Franklin Type A & B confused. I know that on some installations the “rotary” drive is quite obvious, linked to the crank pin the way it is. Seeing the photo of the right-angle axle gear reducer mounted on the axle that the PRR 5399 simply had the rotational drive shaft between the drivers, essentially hidden from view.
This patent drawing shows the Type B if I’m not mistaken.
Franklin Rotary by Edmund, on Flickr
Solid documentation is certainly hard to come by! Looking at the arrangement for the Type A, I can not see where the right-angle drive as shown in the Hagley photo series would have been applied.
Franklin-Type-A by Edmund, on Flickr
There certainly must have been a great deal of head-scratching and perhaps a grumble or two from the Lima engineers tasked with mounting that cam box ahead of the steam chest. From what I’ve read, Franklin (Lima) covered the cost of the installation in hopes of selling the PRR on the idea.
Regards, Ed
The two designs that come to mind are G.J Churchward’s first “Star”, no 40, later 4000 and Deeley’s 999 class 4-4-0. It was not widely used apart from these eleven locomotives in total. Both these locomotive types had inside cylinders and valve gear, although No 4000 also had outside cylinders with the valves operated by rocking arms.
Inside rotary drive to poppet valve gear was quite common with British applications of Caprotti gear, including export locomotives. A number of LMS “Black 5” locomotives were built in 1947-48 with rotary drive from the second (driving) coupled axle.
Peter
Can you, once and for all, resolve the difference between British Caprotti and ‘Reidinger’? From what I know, Reidinger had the driveshaft only on one side, driving both cams (and I don’t think they had the flexible coupling in the center that the shaft in an FM 38D OP engine does) whereas British Caprotti, like Franklin type B, has a separate shaft for each side. Differences in the actual cam follower and valve operation I couldn’t make out from the small drawings I had.