SC and other piston gun repair

Repairs to water guns. Please put repair topics in this forum so that people do not have to sort through so many topics when looking for a repair. If a fix is included in the topic, please add (Fixed) before the topic title to indicate so.
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adronl
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SC and other piston gun repair

Post by adronl » Thu Jul 09, 2009 7:19 pm

Well repairing a piston gun is pretty much impossible if the are already having major leakage so you gotta pretty much rebuild most of it. The pictures that will follow show a slightly damaged but still very functional piston followed by a piston that may never seal properly again. The further damaged piston has been reinforced and reformed but the damage is still apparent even though after being reshaped it looks decent before it was obviously FUBAR.

also I am posting the pictures separately so you wont have to scroll sideways read the text

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adronl
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Re: SC and other piston gun repair

Post by adronl » Thu Jul 09, 2009 7:24 pm

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cantab
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Re: SC and other piston gun repair

Post by cantab » Thu Jul 09, 2009 7:29 pm

Since the pistons are prone to issues, it would seem worthwhile making one end of the PC screw-on, or some other removable coupling. That's assuming such a connection can be had and pressure rated.
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SSCBen
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Re: SC and other piston gun repair

Post by SSCBen » Thu Jul 09, 2009 7:36 pm

Thanks for this adronl. Great stuff. Makes me want to open my SC to see the piston.

I'm not quite sure designing piston guns to open at one end is possible in practice. Large threaded fittings are hard to seal in my experience. It's definitely worth looking in to though. I probably was doing something basic wrong when I had issues.

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adronl
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Re: SC and other piston gun repair

Post by adronl » Fri Jul 10, 2009 5:52 am

Do note that the damage seen is over a progression of time and other factors like failed repairs. The damage begins with a piston cup ramming into a reducing/bell coupling directly as it forces the water out. The angle of the coupling rounds the piston cup in with a concave shape with obtuse angles to more of a convex outer shape with acute angles after repeated high power impacts. This leads to leakage that increases until and overhaul is needed.

From my attempts a repair cannot be done using any type of coupling on the piston chamber. An exception I have not tried is a repair coupling with no ridge and perfectly straight cut ends sanded and filed with very little latex caulk to smooth the bump that occurs. This repair is untested and doubt it world work well.

The rough edges you see are from being rammed into a reducing coupling and from repairs with both standard and repair couplings on the piston chamber. This will mess up the sealing edges of the cups abrading them. This is common in smaller piston guns with reducing couplings as for larger piston guns with non reinforced pistons it gets worse you, get moderate to severe warping of the piston cups and messed up seals.

In my opinion you should stick with a bushing for the output side of the gun which you can follow up with a reducing coupling to get a little better performance. I believe a flat cap or plug are ideal for the end but rounded standard caps are ok. Some damage can occure if you force the seal past the edge of the pipe into the rounded area of a rounded cap or a reducing coupling for a LPD design. Also I believe 3" 4" and 6" piston cups should be solidly reinforced for longevity ( not just a bolt some big washers about 2" diameter and some nuts).

Maybe some people here can come up with differing options of how to do it I already have my method that not just everyone can do with out specialty tools. I make large washers the concur with the size of the piston cups.
Last edited by adronl on Fri Jul 10, 2009 6:00 am, edited 1 time in total.

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