Steam & Excursion > Poppet Valve Sound

Are there any recordings of poppet valve engines?

Was their sound any different than a slide valve or piston valve engine?

I would expect that it would be about the same, as the drafting requirements of the boiler would seemingly be unchanged, however perhaps with poppet valves a lowered exhaust pressure might be possible.

Anyone know?

-JLS

Yes, John, there are records ( now CDs) there’s a CD on PRR steam, and a cut of a single T-1 hauling a train around Horseshoe Curve..
It’s impossible to distinguish the sound from the poppets from piston valves. ( I’ll go thru my CD collection for the CD title...)

The cut on the record is a good medium speed, good performance from 80” drivers...NO SLIPPING...

There may be some discernible crisp, valve events...
But, remember the Caprotti ( “O.C.” — oscillating cam) valve gear was two miniature Walschaerts-like valve gears inside the valve gear boxes....thus, the output shafts to the cams, followers and poppets were following the same sinusoidal timing ( Walschaerts reversing link, and all) as occurs with Radial valve gears. The T-1s were built with the Caprotti gear, using the oscillating movement of a crosshead-connected actuating arm....but, the right crosshead drives the left-side valves, the left side piston & crosshead, drives the right-side valves.

Later, Franklin variants used Rotary drive gears, spinning the cams, and not cross-engine, oscillating scheme. Each return crank, drives that side, respectively.
The rotative cam, replicates that of internal combustion engines.... so, spinning-cam profiles can be manipulated, and ‘customized’ profiles can be designed for crisp events...

Ex-Army 2-8-0, #611, used the rotating cams to drive that gear....I don’t know of recordings of the Army #611, they’d be interesting to hear.

But, recip Steamers, regardless of Valve gears — Radial, Corliss, poppets, Stephenson,Baker, all the rest ...all are designed to control the two power strokes
( per cylinder) so, the sounds are going to be the same...chuff, chuff, chuff, chuff.

With rotary cams, you can virtually eliminate the uneven, inherent, lop-sided tendencies of radial valve gears.
Poppets could be, always, “square as a Die”, at the stack....


W.



Edited 5 time(s). Last edit at 11/12/17 14:35 by wcamp1472.

Both John and Wes,

I have been listening to the subject recording, i.e. PRR steam on Horseshoe Curve for many years (I have the original vinyl record in my collection) , and in my opinion the sound of the T1 exhaust is MUCH sharper and more "staccato" like than ANY of the other locomotives on that record/CD.

Jack,

It’s been decades since I’ve listened to that track, and I was very much a novice...I didn’t know squat about Steamers and valves... [ some would say that not much has changed..]....

You may be right..about the sounds you’re hearing from that beauty...

I’ll give it a listen, now...

W.

T1 Horseshoe Curve recording is on Sounds Of Steam On Horseshoe Curve from Semaphore Records.

Mary McPherson
Dongola, IL
Diverging Clear Productions

Out of all of the operating steam locomotives currently, I would wager that NKP 765 has the sharpest and most staccato exhaust.

Isn't the "Duke of Gloucester" in the UK poppet valve? Pretty good scenes on that video site

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Edited 1 time(s). Last edit at 11/10/17 14:45 by LIL_BUDDY.

Yes indeed BR 71000 Duke of Gloucester has poppet valves. There are many very good, and some very very good clips of The Duke with 500 -700 tons trailing load attacking grades at speed. Back in about [url=tel:2008-2010 71000]2008-2010 71000[/url] got into a bit of a war with stainier 4 cylinder Pacific LMS 46233 Duchess of Sutherland for some speed/time records over some famous tough stretches of BR mainline including Shapp. The Duke reigned supreme in most cases with impressive perfect sharp sticatto valve events. Also, 71000 has a truly amazing rescue and rebuild story from literally being in rusted pieces with motion gone and one cylinder missing at Barry scrapyard.  Original designer but elderly Robin Riddles helped! There is a DVD that desribes the disposition, rescue and second life of this amazing locomotive.



Edited 1 time(s). Last edit at 11/10/17 21:33 by OKTrainboys.

Having a lot of experience with both spool and poppet valves, though in the hydraulics industry, the one thing on
the poppet valves was always the open/close speed issues ie they were very fast. In most cases we had to throttle
both opening and closing rates to reduce induced shock. It's not much a of a surprise to hear that a current steam
locomotive with poppet valves would have a definite staccato sound.

Out

Fast open, close....
Yes, THAT is the identifying characteristic of poppets.
Mostly dependent on cam lobe design/profile.

With conventional Steamers, exhaust always occurs at the end of the power stroke — closing timing, at the end of the exhaust stroke, may be varied depending on the designer’s prejudices/ beliefs about the need to ‘cushion’ the piston before stoke-reversing occurs.

Intake timing may be advanced to some point BEFORE the piston reaches the dead-centers ( according to track speed), but , at starting, its ideal to have steam admission occur AFTER the driver cranks have passed beyond the dead-centers... [ Note: With conventional ‘radial’ gears , the ‘lead’ is fixed. So that when the piston is at dead-Center, the valve will be open by a nominal 1/4” .... a “ fixed lead” ...].

Soooo, the two events, in conventional spool valves, are always connected because of the one-piece spool valve and the fixed position of the ports.
As the engineer shortens the travel of the spool, it reduces the width of the port openings—thus, inducing wire-drawing of the steam entering the cylinders
( not a good thing), but also constricts the width of the exhaust ports
— producing excessive build-up of “exhaust crowding” , or build up of “ back pressure” during exhaust events.

With poppets, the exhaust events can be entirely separated from the admission events. Thus, at the end of the power stroke, the ( larger diameter ) exhaust poppets (2 at each end), pop open — by the design of that cam profile....they stay open for the entire exhaust stroke.... if cam operated.*

The intake events change from AFTER dead-Center opening ( at starting) , to advancing several degrees BEFORE rreaching dead-center ( the ‘lead’) and delaying the closing ( cut-off) during a variable amount , up to about 85% of the power stroke. At high rotative wheel speed, you will be setting the admission for abot 8- degrees before dead-Center and setting the close-event at between 10% to 33% of the power stroke.
Cam operated poppets can have the cam profile designed for that extent of range/ power selection.

The ‘sound’ that we hear is strictly the sounds generated as a result of the exhaust poppets and the cam profile...

We can’t hear the steam flow on admission....

So, the separation of the two cycles is the REAL key to poppets. However, the increased power available at higher speeds , definitely makes poppets THE choice—- like about a 50% increase.... see PRR K4 5399, and late 1930s AAR power tests on level, tangent track...

Yay, poppets...

W.

*The PRR T-1 locos we’re built using the ‘ Caprotti ‘ design . The poppets were opened and closed by the reciprocating, crosshead-connected levers....operating Walschaerts-like reversing links, and producing the related sine- curve speed variations of the valve events.....

Rotary operated cams, opening and closing speeds are determined by the shape of the cams, independent of the piston speeds, very free-ing design concepts...



Edited 7 time(s). Last edit at 11/11/17 16:59 by wcamp1472.

Wes wrote:

> So, the separation of the two cycles is the REAL key to poppets. <

That, and the quickness of the valves opening and closing is what got me to thinking whether that might result in a different sound.

I don't believe a piston valve was ever developed that separated the settings for opening and closing of the valves. However, the A. J. Stevens valve gear for slide valves did. It was tried by the Southern Pacific, but I don't believe it got widespread use - like, maybe only one engine.

The only steam engine I've ever heard with poppet valves was an industrial engine with Corliss rotary trip valves. Being an industrial engine a strong exhaust draft wasn't required, therefore very low back pressure and NO chuffing. All you could hear was the clicking of the trips.

-John

YES!!!

The WildMary, at their Hagerstown,MD, Roundhouse had a beautifully functioning stationary air compressor...Corliss valve gear...clicking sound was the only noise ...I watched it for hours, on end...

The machinist in charge, was dismayed by a slight click at the flywheel crankpin....he told told me the crank’s bearings were getting worn...but, not in plans to repair...

House, power plant and wonderful facility all gone, now...
So glad I got to spend so much time there, working on Ross’s steam & with the wonderful WM workers...

I’ll never forget that clicking air compressor, and the Corliss valves...steadily spinning flywheel...

Yes!!!!

W.



Edited 2 time(s). Last edit at 11/12/17 15:14 by wcamp1472.