Hello,

I have always been facinated by mechanical interlocking towers installations.

In doing some reading on typical equipment used, the pipeline rod installation was between the tower and the switches/signals was interesting. They had a device called a compensator to take up themal expansion of the pipes during hot days. They used a compensator when the pipe runs were long.

I had a question on the pipework. Did they rely soley on the tower levers being latched to secure the switch points or signal positions? (In signals I am referencing mechinical semaphores). If you think about it, if the pipe was under compression, the lever would be fixed on one end and a switch point would fix the other, forcing any thermal expansion against itself. However, if the pipe was under tension, thermal expansion would have the effect of lessening the tension. If this was a signal, it would tend to move the semaphore blade. If it was a switch it could have more disasterous results. The lessening of tension could cause the point to not be tight causing a derailment. How did they prevent this from happening? Was there a secondary lock on the switch to prevent it from loosening....ie a second lever in the tower to engage this lock?

Maybe some folks from the Lemo Tower project read this forum and could reply?

Thanks in advance for your response.

Regards,

Randy


How

Randy -

I am not the guy that is doing the restoration work on Grasselli Tower that our museum moved to North Judson last year. BUT, our signal guru has done some preliminary restoration work on the tower including re-hooking up all of the levers. In his demonstrations that I have witnessed, he has always seemed to throw a lever for the LOCK, before he could move the lever that controlled the switch or signal. He can explain it much better than I and you should contact him. I don't think he reads RyPN, but if you send me a PM, I'll see if I can find his e-mail address.

Les

The problem of expansion and contraction of interlocking rods is solved by the use of double bellcranks and reversal of direction of portions of an interlocking rod. If a rod coming from the tower is pushing, then goes through a double bellcrank, now the next section of rod is pulling. As long as the lengths of pushing and pulling rods are somewhat equal in length, any expansion and contraction will cancel each other out and only result in a slight change of position of the double bellcrank, and not affect the positions at the ends of the rod which are held fast by locks at both ends.

Years ago Model Railroader magazine carried a several part article about interlocking plants and modeling them. It explained how the actual interlocking worked and how the linkage rods were installed. The purpose of the article was to enable a modeler to make an interlocking installation on a model layout. However, I have recently talked with a retired Santa Fe signal system maintenance engineer who said once he found that series it made his life easier as it explained how the mechanical plants operated.

Brian -

Happen to know the MR issue dates?

Les

It was in the Jan 04 issue by Bill Darnaby.
http://index.mrmag.com/tm.exe?opt=I&MAG ... t=5&sort=D

Alan

For the switches in a mechanical interlocking plant there are two levers. One locks or unlocks it, the other throws it between normal and reverse. The locking function typically has enough over-travel beyond a functionally locked position to deal with minor changes in length of the operating pipe. Once the switch(es) are aligned and locked, that will determine which signal levers can then be moved to a clear position.

When mechanical plants were replaced by electrically controlled interlockings, that same "unlock, move, re-lock" sequence is performed by a switch machine, either pneumatic or electic powered. Relays that repeat the aligned and locked positions of the switch then allow the appropriate signals to be cleared.

That's a nice article, but more about modeling the outdoors details of the rodding, etc. I think the article being referred to was the one published in Model Railroader sometime in the late fifties, that actually described how to build a working locking frame. Unfortunately, the Model Train Magazine Index isn't bringing up a citation, but the fifties era article was just mentioned in the latest issue of Model Railroad Planning

The Railway engineering and Maintenance Cyclopedias have a short section on Interlockings, both mechanical and power(pneumatic and electric). The 1939, 4th ed, has good description of the levers and interlocks and most of the components. It does reference an AAR signal section for more information. The 1942 edition the mechanical section is very short. I suspect the earlier editions: 1921, 1927 and 1931? would include more related to mechanical interlockings.

It was some time ago. If I dig out my old issues and spend time going through them I could find it. I've been into model railroading (at times not all that active) for over 50 years since I was in grade school.

I had tried to use the Model Train Magazine index and could not find it. Even tried looking at the individual issue listings for every second or third month. It was the one about how to build a working set-up for your model railroad and there were special Cal-Scale castings for the pole finials, etc. It was good because it showed how the linkage was set up to require signals to be changed prior to moving a switch point and then only then be cleared again.

I just spent more time looking at the individual issues at the Model Train Magazine Index.

And I think I found what I remember:
Model Railroader January, 1961: "Mechanical interlocking and signaling"

Model Railroader February, 1961: "How to design your interlocking frame"
Model Railroader March, 1961: "Track diagram and interlocking cabinet"
Model Railroader April, 1961: "Semaphores with lost wax parts"

I just tried the keyword search again and "interlocking" did not return any of these articles.

Hello All,

Thank you all for the thorough and extensive replies! Very helpful and interesting.

In reseraching further, it appears they called the double bell crank compensators..."lazy jacks". Here are a couple of Google Book resources if you want go deep.

Here is a book from 1921. Mechanical interlocking starts on page 36, Chapter IV.

http://books.google.com/books?id=aHT6CCypKOgC&pg=PA36&dq=mechanical+interlocking+towers&as_brr=1&cd=1#v=onepage&q=mechanical%20interlocking%20towers&f=false

Another from 1907. Signaling and interlocking starts on page 129

http://books.google.com/books?id=ddCoMg5iF-IC&pg=PA288&dq=mechanical+interlocking+lazy+jack&lr=&as_brr=1&cd=15#v=onepage&q=mechanical%20interlocking%20lazy%20jack&f=false

I can't image the challenge these mechanical plants were to keep operable in the winter, especially like we been having in the Northeast. You would have to keep one person busy just keeping the pipeline from freezing up. What a mess!

Thanks again!

Regards,

Randy