This is a clone of a Walvoil SD11 monoblock DCV.
It's a good clone, by the way. Decent quality, a great price, and probably the best budget DCV I could get (at least at the moment of this writing). I've been using them for years for simple stuff, like front loaders, log splitters, etc.., and I've had zero problems. But this is not a sales pitch, this is a technical article about the radial clearance of spools in spool-type DCVs, and I will be using this particular clone to illustrate how even a seemingly insignificant increase in radial clearance leads to a surprising increase in leakage.
So, I needed to find an economical two-section DCV solution the other day, and one of the sections had to be single-acting. We stock tons of Walvoil valves and the respective parts, but the "economical" part of the client's request was imperative, and so I thought to myself - "I wonder if I can fit the Walvoil's single-acting spool into one of these clones?"
I could also machine the spool, of course, and we do have all the necessary tools in the shop to do it right (although even a simple girding stone would do the job if I were "in a pinch"), but why waste time machining spools when you have parts lying on the shelf?
Here are the two spools one next to another - the original Walvoil at the top (single-acting on A, B plugged, three positions), and the cloned-version at the bottom (closed center, double-acting, 3 positions):
They look "swappable" to the naked eye, but when I measured the spools, I saw that there was a 0.03mm difference in their diameters. Walvoil's spools measured exactly 20.00 mm in diameter (I grabbed other Walvoil spools from the shelf and measured them as well - and they all had 20.00), and the "cloned" version measured 20.03 mm.