Does anyone here have any information about the Pettibone Mechanical Switchman? It is/was a hydraulic device for a spring switch that had an oil-filled cylinder that dampened the movement of the points. A friend has asked about this. I remember seeing one somewhere, but I don't know how they worked. He is especially interested in how one adjusts the device and what type of oil was used in it.

Thanks.

What he's describing is the device that allows a "spring switch" to operate. There is a coiled compression spring inside that round thing. Spring is relaxed.
The switch points will be lined for straight track movement. A movement wanting to make a trailing point move from the diverging route onto the main track can pull right on thru that switch and not line it for their movement. The switch points will be forced over by the weight of the car.... the force of that compressed spring will return them back towards the stock rail and lined for main line movement... but not real fast.
They behave like an automobile shock absorber... not sure if there is oil inside the unit as a dampening agent or not, but the points don't "slam" back shut... they go back nice and slow.
When the last car of the train gets out on the main, the spring returns the switch points to the normal position ready for action.
Spring switch mechanisms only "spring" for movements out of the siding. You can't hand line a spring switch for a diverging move... then run thru it from the main line side. Torn up mechanism is what you'll have by doing that.

Other models can work as spring switches from both Main and siding.

As do the ones at IRM. IRM "automated" its standard ride back in the late sixties with a pair of these, and as far as I know they are still in service. You can do a spring switch with just a spring arrangement in the throwbar, but the points come crashing back after each and every wheel trails through; very hard on the switchpoints. With the dashpot on the throwbar, the first wheel opens the switch, which stays open long enough for the second wheel to keep it open, ad infinitum. The only thing to be aware of is the points take a minute or so to close after the last wheel clears; quick reversals by hotshot throttle jockeys can put things on the ground in the switch.

As for adjustment, while I haven't had to do it, there must be a metering valve somewhere, possibly under the cap. Any light hydraulic oil should be fine; if the points return too slowly during the winter, you need lighter oil.

The dampening unit has oil in it. TVRM got three spring switch units from the Southern years ago-reportedly the Southern gave them to us after having removed them from service with unsatisfactory results. Our shop made a couple of minor modifications and has had satisfactory use of the switches for years. The points will spring in either direction, depending on which route the switch machine is lined for as these switches are on a wye.

They're also strong enough that they will derail as speeder rather than opening. Add in the slow closing (Hey, I think I can make it before it throws!) along with the once it does spring shut, a speeder is going to derail when it hits it, and you have a recipe for disaster for somebody trying to "sneak out" after a passenger train instead of lining the dang switch which is too much work.

Add in a nice full load of passengers who have a grandstand view, and it made for a funny situation once we determined that the only thing injured was the speeder operator's pride as he ended up sitting sideways on the mainline. (No, I won't comment on where or when...)

A lot of the problem depends on the speed, guessing your presumably slower speeds help. The Waterfront Streetcar in Seattle had two fancy spring switches on one of the passing tracks. They were supposed to be able to work in either direction. I spent months fiddling with them, adjusting them according to the manufacturer's specifications. They'd often go over center, leading to a potential head on collision situation. Fortunately, they were aware of the problem and a speed restriction averted any disasters. They'd test OK, but as soon as a streetcar making any speed, and it didn't take much at all, hit it, the forces were much stronger.

They did, amazingly, find out that one of their Melbourne W2 trams could go through the passing track with one truck on the main, one on the siding, and stay on the rails. Luckily, there was no car being passed (light service time) and no poles between the tracks.

Finally, they sent a rep out for someplace in Europe, I think it was in Luxembourg. He was going to show us how to adjust them properly. We went through the installation instructions, measuring and adjusting the spring tension, shimming and measuring, etc. etc. "There, that should do it, try it now!". The first car through hit the points and "wham", over center it went and stayed thrown in the wrong direction.

We ended up leaving them adjusted in a manner that only allowed them to be thrown one way and function as a spring switch, which wasn't really a problem. Eventually they came out with a retrofit kit that added a hydraulic dampener which solved the problem.

During some of the work, I was talking to one of the manufacturer's reps and said "Is this the only one of it's kind in the US? I've never seen anything like it!" He said "No, there are two of them." Wondering if maybe the other place knew something I didn't, I said "Oh, where's the other one?" He pointed to the opposite end of the passing track and said "There's one over there." D'oh!

Thanks to all who responded. I think we've got our problem solved.

Wayne Laepple

Well, that's called a "variable" switch. When run through, the points snap over and stay there definitely. If an operator were to hypothetically roll through a variable and then back up, there should be no problem with that. I would call them "the norm" in street railways. If the switch is against you and you are trailing, just run through. If it is facing, grab a switch iron and throw it over. That is why most streetcar crossovers are set up 'trailing', so the crossing-over crew doesn't have to throw the switches back to straight, passage of the next car will do that automatically.

Spring switches in street railway service are also not unusual, it is going to occur anywhere there's a passing bubble, which will occur on many lightly traveled lines which are single track. What is unique in that application is the requirement to spring BOTH ways - as usually you only ever spring one way, as you are beholden to the flow of street traffic.

I wonder if the combination of the unusual request for a 2-way spring switch, combined with translation errors, led the vendor to thinking you wanted a variable.

No, this was definitely not intended to be a variable switch. It was intended to function as a spring switch, but it could be lined for either route by removing the mechanism cover (it was in the street) and using a large bar to line the switch. Once thrown in that direction, it would then function as a normal spring switch, always lining back to the route it was thrown to.

No, there was no language problem, and the manufacturer insisted that it should be able to work as a spring switch, and be lined for the route of your choice without the need for adjustment. In fact, once they added the hydraulic dampener, that is exactly how it worked.

As to WHY they wanted that functionality, I'm not certain. I think the concept may have been to equalize wheel wear, as the cars were never turned, but even that doesn't make much sense. Traffic flow wasn't an issue, since while the track was in pavement, it was on a reserved section of the street.

Of course it wasn't unheard of to have mis-understandings on the line. While it didn't happen with the spring switches, I got a panicked call one day about some frogs.

They called and said "We had a consultant come out and look over the line, and he says our frogs are completely worn out and must be replaced immediately!"
I said "Oh, really? What's wrong with them? They looked fine when I checked them last week..."
"Well, he says they're so completely worn out that the flanges are hitting the frog!"
"Uh, yeah, that's a tramway frog. It's DESIGNED to do that, your specifications required them, and they most likely cost you quite a bit extra to have made and installed. But they're working precisely as designed. They lift up the wheels and prevent banging at the frog."
"Oh, they are? Let me get back to you..." Late "OK, I talked to the engineer and he said you're correct..."
"Yep, the next time somebody else checks the track, tell them not to use mainline railroad standards on a streetcar line, OK? You've got vertical curves out there that don't meet FRA standards either, but you're not under FRA"

The spring switch on UP's Harvard Sub at Harvard Illinois always worked both ways. It goes from double track mainline to single main line protected by switch point indicators on all routes. Same set up at Kenosha Wisconsin on the UP's Kenosha Sub . Gurnee and Park City Illinois at both ends of the double track on the Milwaukee Sub also had hydraulic cushioned springers . Since the Harvard and Kenosha springers were in yard limits they weren't always lined for normal routes. If I didn't have a conductor or helper with me at Harvard while pulling more than three cars with my American crane and wanting to cross over from track 2 to track 1 I'd walk or drive up to the springer , throw it for track 1 , go back and hop on the crane . Travel it and cars north through the springer past the switch point indicator , waiting on the road crossing about 10 seconds for the indicator to show me that the points were now lined properly and head south onto track 1. I'd then more often then not walk or drive back to reline the spinger before the next scoot arrived so as to not make its conductor have to do it. It's left hand running on the old CNW. Some of the scoot conductors would tell me don't bother they'd throw it instead. They were a great bunch of guys.