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:
Franklin by Edmund, on Flickr
Regards, Ed
M636CAfter the boiler improvements, it was tested against a standard K4 5341. At 40 mph, it was 16.2% more powerful in indicated horsepower. At 60 mph,17.1% At 80 mph, 22.9%
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.
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 knowledge none of them were subsequently converted to Franklin System so the issues were more than in the cambox and general frailty of the actuation system.
The K5s were unfortunately timed: they came just after the massive orders for K4s in the late '20s, and had to sit out the capital dedication to mainline electrification, by which point the frenzy over duplex augment reduction on large passenger power (and perhaps the bad taste of the ACL R1 fiasco) was in full cry. By the time the results of Timken lightweight rods on eight-coupled heavy engines were becoming evident PRR had already committed to something larger and smaller at the same time!
Since the K5s were orphans they weren't used as testbeds for much of anything, being stuck on the Northern Central where high speed was unimportant and relatively low FA already a concern. It literally took an act of Congress to get stokers put on them, which perhaps shows up mistaken design priority better than any other thing. It would be highly interesting to see what a K5 modified as 5399 was would have been able to do ... just that it would neither be used to advantage or serve as an example for service conversion or new practice any more than a K4 conversion would.
Now, I still don't quite understand why PRR didn't do any poppet/lightweight rod conversions on the M1 chassis: that would promise to be groundbreaking.
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
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?
M636C5399 had the cams driven from the crosshead, the Walschaerts valve gear having been removed.
RC gear, of course, has neither a substantial shrouding of valve openings or a periodic reversal of momentum of the cam to accommodate.
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 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.
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 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.
5399 had the cams driven from the crosshead, the Walschearts valve gear having been removed.
Even before the boiler improvements, 5399 could haul a 1000 ton train at 94.7 mph under AAR test conditions. I seem to recall that this was about the same as the original UP 800 when tested.
It was allocated to heavy trains which would normally have required two K4s. On 5 Nov 1939, it worked The General weighing 940 tons, saving 21 minutes on the schedule at an average overall speed of 65 mph.
After the boiler improvements, it was tested against a standard K4 5341.
At 40 mph, it was 16.2% more powerful in indicated horsepower.
At 60 mph,17.1%
At 80 mph, 22.9%
At 100mph, 46.8% (4070 ihp against 2770 ihp)
Of course, if 5341 had had the boiler improvements and had the piston valves been enlarged, the difference might not have been as great.
In France, although many locomotives were rebuilt up to the standard of the Paris Orleans 3700, it was found that dramatic increases in power and economy could be obtained simply by applying improved Low Pressure piston valves, along with improving the steam flow from the boiler to the HP cylinders and between HP and LP cylinders. This was much cheaper than the full Chapelon treatment.
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
daveklepperWhat Type poppet-valves were used?
What Type poppet-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.
What Type popet-valves were used?
No other K4 got rebuilt the way 5399 did. One or two others got poppet valves.
One advantage of a front-end throttle is that it reduces the response time of the locomotive to throttle changes.
1. 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?
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