This Benjamin hand pump came to me a short while ago having failed after the owner had only used it about 5 or 6 times to pump up his Disco. I have been waiting several weeks for the rebuild kit to arrive from the supplier of the pump - Sun Optics, in Texas. I first tried to obtain the kit through the Canadian Crosman Distributor, but after several weeks of trying without success, he just gave up, and gave me the contact info for Sun Optics. I called them, and explained the situation to them, and that neither I, nor the owner of the pump were pleased with the lack of interest shown by them in providing the rebuild kit. I was assured that they would send a kit to me ASAP, free of charge, and after almost a week and a half, I had pretty much given up hope on receiving it. But today, I was pleasantly surprized by a package in the mail - the long awaited rebuild kit had arrived.
Having given up on ever getting the kit from Sun Optics, I had already taken the step of trying to identify the correct o-ring sizes for the pump, so that I could order them through my regular source. As I cleaned up the old o-rings, it was clear why the pump had failed. There are 13 o-rings in the pump, and every single one was badly abraided and nicked. They were all so bad, that it was difficult to get any proper dimensions, because in some cases, the o-rings had an eliptical cross section, rather than round. Further investigation revealed the cause - the sliding surfaces of the pump were abysmal - scratches and gouges everywhere - it appears to me that these surfaces were never polished smooth, thus, the o-rings were ground away in no time. Some o-rings had deep nicks in them that could only have occurred during assembly. The pics will illustrate the deplorable quality encountered.
The o-rings - note the deep abrasions, and tattered edges, as well as deep nicks on them. The lower left pic is the final stage check valve seal - almost half the top section is missing. The bottom right pic is the 5.5 mm rubber ball check from the second stage piston. This is not included in the
rebuild kit, because as the representative put it, "that ball will never wear out". Apparently someone forgot to make this badly abraided ball aware of that.
The ball check seat is completely covered in sharp, jagged burrs, and almost appears like it was machined with a hammer and chisel. Two very light, plastic washers act as retainers and I presume, a tensioner for the ball check. Both of these are in pretty rough condition, and should be replaced IMO, but alas, these are also excluded from the rebuild kit as "un-necessary". The circlip on the left is the one from the pump, and is exactly as found - it is believed that this pump was a "factory refurb", yet sold as new. (more evidence of this to follow) It appears that the circlip was pryed off, rather than the use of the appropriate snap-ring pliers. This is exactly how it came off - I only gave it a flick with my fingernail to remove it. The brand new circlip on the right shows how badly mis-shapen the OEM unit is.
The final stage piston is clearly canted on the end of it's rod - this can be evidenced by the heavy wear on the top rear edge of the piston in the
upper pic, and the lower front of the piston in the lower pic. The front of the piston is no longer round, but eliptical. The back up washer for the piston seal is also not included in the kit, again, presumably because it was not considered "needed".
The OD of the intermediate piston has numerous tooling marks leading me to think that it was held in a bench vise at some point in time. (Again - supplier refurb?).
This is the second stage rod - it is not hard to see why the o-rings have been shredded. From top to bottom, the top section of the rod, the middle section, and the lower section.
The first stage rod - lower, and mid section.
And finally, the outer tube, showing the obvious use of slip joint pliers on it. The owner tells me that this is how the pump came out of the box when he bought his Disco package, but really hadn't paid it much attention until I pointed it out when he dropped the pump off in person. This is another reason that I firmly believe that this particular pump is a supplier refurb, and IMO, should never have been sold as "new" with the gun.