If the handle of your Pista pump rises on its own after a downstroke, you most likely have a leaking check valve. Silca will happily sell you a replacement, but with no instructions.
You may find that, after you remove the plug that houses the check valve stem using a 14-mm socket (pink arrow above), that the old valve stem won't come out. That was the case on my ~1990 pump. At left below is the plug with the original valve stem, and at right is the replacement from Silca. I asked Silca whether it should come out easily, and I was told I probably had dirt and grime in there (which was also the cause of the leaky check valve).
Well, it turns out that the end of the original check valve stem has a "bell" on the end, and the sleeve that it goes into in the plug is crimped so as to capture that bell and prevent the stem from just falling out.
What you have to do is to carefully use pliers on the long axis of the crimp to make the sleeve more or less round again, and then you can yank out the old valve stem. The new stem, not having a bell, just drops right in, and there's no need to re-crimp the sleeve. Now my pump doesn't backflow. Huzzah!
[NOTE: It may be possible to purchase a check valve with the end plug elsewhere, in which case these instructions are moot, but Silca doesn't sell you a replacement plug.]
I offer this because I found no mention of it online, despite numerous instructional resources for other aspects of servicing Silca pumps. Let's see if Google effectively catalogs this page and helps someone else trying to keep his beloved track pump alive. Ciao!
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