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Need info on Christensen hydraulic press

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  • #16
    Doc, could the snap ring be the upper travel limit of the pump? I have had a couple of piston hand pumps apart and they either had a heavy snap ring or a reduced upper shaft diameter with a sharp shoulder as the stop.
    How tight is the fit between the piston and the cylinders wall? If the pistons edges were polished and then the cylinder honed to a very close tolerance fit a HV low pressure pump would pump oil at low pressures.
    Dan

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    • #17
      Originally posted by Lu47Dan
      Doc, could the snap ring be the upper travel limit of the pump?
      -It does, and that's what I'd assumed the ring was there for. My question is, that it's sustained damage from excessive force, and from the direction as if someone had, in fact, been slamming it against the upper threaded cap repeatedly and forcefully, but there is no trace of matching damage on the cap itself. No wear, no peening, no marks, nothing.

      That makes me think there was something between the cap and the snap ring, though I can't think what that might have been.

      How tight is the fit between the piston and the cylinders wall? If the pistons edges were polished and then the cylinder honed to a very close tolerance fit a HV low pressure pump would pump oil at low pressures.
      -It's pretty close, and I have no doubt it'd pump oil with reasonable efficiency. But without a seal on the piston and no seal on the upper cap, there's nothing to keep fluid from building up above the piston, and then being pumped overboard through the cap. There has to be a seal in there somewhere.

      Doc.
      Doc's Machine. (Probably not what you expect.)

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      • #18
        Next question: The two check balls between the pump cylinders and the output to the ram are held in place with threaded plugs with a long "pin" on the end. The pin I'm presuming limits the travel of the check ball, and the plug is a straight thread with a copper washer for a seal.

        One of the two plugs has been damaged- it looks like somebody may have dropped an extra check ball in place, or one considerably oversized, and tried to tighten the plug back in place.

        This distorted the threads slightly, and actually bent the pin (which is just mild steel.)

        I was going to make a new plug, but it's an oddball thread: approximately 19 tpi, and .517" OD. It's neither a standard US thread nor a metric- at least according to my metric thread pitch gages.

        What is it? Whitworth? British Straight Pipe?

        Doc.
        Doc's Machine. (Probably not what you expect.)

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        • #19
          Bsp

          Looks to be British Standard Pipe

          http://www.oldengine.org/members/diesel/Tables/bsp1.htm

          ?, on the linked chart 1/4" and 3/8" are 19 tpi with the 1/4" being .518

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          • #20
            I think I'd consider making a new piston with opposing seals. Then ditch the snap ring for a spacer and rubber washer or some type of spring. That way the stop has a little give. Something like a valve spring comes to mind as an option.

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            • #21
              Doc, I think you do need to make a new piston for the pump, just remember to allow for the added thickness of it.
              For the plug for the check valve, If the threads are not damaged past the point of use, then why not just add a new stop rod to the plug. If I read the post correctly it has a copper compression seal on it, correct? Replacing the rod would save you from cutting the Whitworth(?) threads.
              Dan.

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              • #22
                BSP G or R 1/4" plugs are readily available from the plumbing section of local hardware store, unless you guys across the sea use something of your own.
                Amount of experience is in direct proportion to the value of broken equipment.

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                • #23
                  Russ- Yep, looks like it is BSP. Thanks for the link.
                  Boost-That's my current plan, at least for the moment. The bore is 1.571", which is closer to 40mm than most of the fractional-size seals that McMaster shows (thanks Weird) so I'm trying to find a workable seal before I make the piston.

                  I'll probably leave the clip there, so the piston won't be taking the strain- the threads on the end of the ram are only a bit bigger than 1/4-20. The spring's a good idea though...

                  Question though- what do you mean by "opposing" seals? I was given to understand a lip seal worked best when there's the greatest pressure differential between the two sides of the lip.

                  Dan- that's what I'll probably do at this point, but as I said, whoever tried to mash it in place also slightly distorted the threads of the plug. I'd have preferred to replace it if I could, but it looks like that'll likely be more trouble than it's worth.

                  Doc.
                  Doc's Machine. (Probably not what you expect.)

                  Comment


                  • #24
                    Originally posted by Doc Nickel
                    Russ-
                    Question though- what do you mean by "opposing" seals? I was given to understand a lip seal worked best when there's the greatest pressure differential between the two sides of the lip.

                    Doc.
                    Two seals like a two way hydraulic cylinder. One seal may be fine, but I would be worried about raising the handle too fast and sucking some air past the single seal. One above it facing the opposite direction would take care of that.

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