There is a difference that I have remarked on the pilot (AKA cowcatcher) of older (ca. 1860s) steam engines and newer ones (late 19th- to mid-20th century). On the newer ones, you typically - nay, almost univerally - have a bona fide coupler, and the pilot will be relatively short. See this fine example from Canada.
However, in the older ones, the pilot is longer and instead of a coupler as we would recognize it, there is a bar extending along the diagonal lead edge of the pilot; this can apparently be raised and typically seems to have a hole on its tip. See for example the replica of the famous Union Pacific No. 119.
I would have several questions about these:
I’ve always suspected that the diagonal bar on the older model of the pilot was some kind of coupling device (e.g., to attatch it to another engine). Am I correct or did it serve another purpose?
If the bar described in the previous point did indeed serve a coupling purpose, would it have been possible to use it for the engine to push a whole train, or only to be hitched to another engine (the bar looks like kind of a weak structure to be used for pushing purposes)?
For that matter, would the more modern version of the pilot with the honest-to-goodness coupler have commonly been used on a North American steam engine to push a train, or mainly just to hitch it to a second locomotive? I ask this because you almost never see a picture of a North American steam locomotive, except perhaps a switch engine, pushing a train. However, I have seen multiple pictures of e.g. European steam locomotives pushing trains. These often don’t have a pilot, but rather bumpers and an honest-to goodness coupler in front (of a different kind than in North America, more like a hook and loop system).
In the US, steam engines were often used as pushers as helpers to get trains up known steep gradients, then uncoupled. Sometimes on very heavy trains on steeper grades, one might see helper engines cut in to the middle of the trains as well.
In any case, it’s handy to have a coupler in front to facilitate switching moves for even a “road” engine. On the more modern steam, front couplers were retractable ( they either flipped up/down or swung in/out so as to keep the front pilot “clean”. Here is a photo of one with it’s coupler in the out position on a restored N&W 4-8-4. N&W 611
OK, so they could be used for pushing. What about the bar on the diagonal of the older type of pilot, then? Was that some kind of coupling device or did it have some other purpose? Could such a long thin bar be used for pushing as well, or only for being hitched to another engine (or only for being towed?) And if the bar I’m talking about was in fact a coupler, how would it be attached to the other coupler? By means of a pin? Or would it be attached to something other than a standard coupler? In case it’s still not clear what object I’m referring to, the swivel bar on the diagonal of the cowcatcher is clearly visible in the first two pictures on this page.
According to Wikipedia, the Janney coupler wasn’t invented until 1868 (the year #119 was built) and patented in 1873 and didn’t become standard until much later. What you see in the photograph might be a “link and pin” coupler (the type prevalent before the Janney coupler. A close look at the photo seems to show a hollow end to the bar with a hole in the top for the insertion of a pin.
That black bar does not like it could support any significant compression. So if it were used for traction purposes at all, it might be used to pull the loco, or perhaps to support the weight of the cowcatcher when it was removed - but it would not be able to push anything much heavier than a cow.
There was also a process known as ‘poling’ back in the earlier days ot railroading (outlawed now of course due to OSHA and countless other safety regulations). A locomotive on a parallel track could push a car along the second track by means of a long pole that would fit into a ‘poling pocket’ on the car being moved (see illustration here or video clip here), so you might be seeing something like that as well.
I just came across a documentary about the construction of the replicas of the Jupiter and the 119. I started watching it and got an answer to part of my question. Here at 1:13 to 1:22, it shows the 119 pulling the Jupiter. The rod that I described above is being used to attach the Jupiter to the 119. So like eburacum45 said, it could certainly be used to pull the engine.
Which does happen – you don’t just get in and press the starter button on those engines, so they are pulled/pushed in and out of sheds. I was trying to remember if I’d seen something like that in use, but nada.