So, I went to Lockridge Lumber, the closest purveyor of doorknobs. One of my former students was called up as the expert and he showed me a quite complicated mechanism totally unlike the innards I was looking at in my utility doorknob problem.
I bought a new doorknob and a file end large enough to trigger the mechanism in his product.
Needless to say, that method did absolutely nothing in mine. I kept trying things until I managed to break off the back end of the plastic casing.
Then I tried jerking the thing out backward, unsuccessfully. Upon examination of a nearby door, I found there was a slight plastic flange around the edge of the part that slips into the door latch. Even with the end broken off, I could not get the latch to release. I broke away more and more of the plastic that was in reach, exposing more and more of the inside mechanism, but still could not make it release.
Obviously, this was not happening because of something broken in that part that was to hook the latch and drag it backward. I destroyed all of the black plastic casing I could reach, then went to town and returned the library books, etc.
When I came home, I walked around the house, and since the mud had dried up, was able to get into the utility room from a standing start in between the new deck supports. From that side, I had access to all the rest of the tools in the house, and soon had broken the latch into so many pieces that everything but the residue of the black plastic case came out.
The cats were dying from withheld affection, so working around them was quite a trick, but eventually I got the door open.
I have the proper parts to install a working doorknob identical to the ones in the rest of the trailer, or to put in the more up town version my former student sold me.
Right now, momma kitty, the only one with a working brain back there, has not figured out that she can insert a paw underneath the door and exit at will. J. is supposed to come down tomorrow and work on the deck, so maybe we will consult about which doorknob to use. I would really like to replace all the interior doorknobs at this point. I have NO ROOM in this house that I really want to be locked out of, (or, heaven forfiend, locked permanently INSIDE of) and if the utility room door is any example, I would be unable to solve the problem in the same manner if that happened in a bathroom, closet or bedroom, as I would not have a convenient outer door to allow access to the other side.
Scary! Imagine being trapped in a bedroom, bathroom, or closet, not because the door was locked, but because of el cheapo original equipment, living alone, on summer break, and being in there without a phone. I'm not expected anywhere until mid August once Mom and Aunt C's visit is over.
Look on the bright side:
That might be one way to get the weight off...