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I wasn't going to post these up quite yet, but since Charles mentioned them in another post I figured I'd show my progress so far.
This all started out by trying to get the Accucraft pop safety I have to shut off with less pressure loss. The more I though about it and the deeper I got into it making my own safety just seemed like a better and better idea. Also, since my K27 was converted from an electric engine, the steam dome just sits on top of the boiler jacket if I bother to put it on there at all. The solution (to me) was to try and make a scale sized valve that would stick out of the top of the dome that would look good and hold the dome in place. When I get the valve working right I'll make a second one, that way I'll have two valves holding it in place and I can set one at just a little higherpressure than the other. Just in case.
The safety modelled on the Accucraft K27 appears to be of the Consolidated type (Pic taken from the Strasburg railroad site):

So here is the lineup of valves that I have now. From the left to the right are the Accucraft pop safety, my first prototype, the current valve with the same shutoff issue as the Accucraft valve and the decorative Accucraft valve.

Here is a picture showing all of the internal parts. From the top down are: The pressure adjustment screw with its jam nut, the top of the housing with the vent holes, The bearing cup that the pressure adjustment screw pushes against the spring with, the spring, the cup for the ball that the spring pushes against, the ball and the lower housing. For reference, the adjusment screw is a 1-72 and the bottom-most threads are 5mm x.5.

Here is a picture showing the overall height of the valve. The screw would be in quite a bit further for its intended operating pressure of 65 P.S.I., and in use hopefully only about 1/16" of the bottom hex will be visible.

And lastly a picture showing the opening between the lower and upper housings that the steam exits through.

The problems so far:
The orignal base was bronze instead of brass and I managed to dent the stainless steel ball trying to seat it.
The new base wouldn't seat against a dented ball. A new ball was stolen from a different project and worked at first, only to prove it wasn't stainless afterall and promptly rusted.
The differential between blowoff and shutoff was about perfect at ~5P.S.I. on air, and the first one or two pops on steam. After those initial pops on steam the pressure differential gradually rises to ~20P.S.I. At this point its not clear to me if I'm losing tolerances as the parts heat up or if its a fundemental design flaw. Will have to do more research and order more stock as these were just made from scraps.
 

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To save you hassles in the future, keep a sacrificial ball just for seating then when you have done that drop in a brand new fresh one. S/S balls are available for about $2 for 10 from Maidstone Engineering Service who give a fabulous mail-order service by return, I will order on a Monday and usually get the package here in Canada within 5 business days.

David M-K
Ottawa
 

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Discussion Starter #4
Thanks Jack. Having large engines in 1:20 and 1:13 (the main scales I'm building in) I don't see why we shouldn't have close-to-correct size parts that look and work well.

Thanks for the tip too Dave. I do have a few balls around somewhere. Had i found them I would have done just that but the group of them pulled a dissapearing act. I wonder if having a rough ball is giving me some of the problems as well.
 

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Also try Cole's Power Models for SS (and bronze) balls.

Larry
 

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Justin,

For 3mm stainless balls...I've found www.smallparts.com to be some of the best prices on the East coast. $7.00 for a bag of 100, in sizes from 1mm to 5mm. Accucraft uses 3mm balls in their safeties, so I think that's what you want for yours. The balls come in varying hardnesses, from 302-440c stainless.
 

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Discussion Starter #7
Thanks guys. I have (or had, they may have been accidentally thrown out in a cleanup) a bag of 1/8" balls that I had ordered from Small Parts. I do have a 3/32" ball that I may try instead. It seems to be more of an approriate size for the diameter of the hole in the bottom housing.
 

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High tech plastics in steamers. Nitrile balls appeal in clack or check valves, conform to seat better than SS. Another high tech polymer, Teflon PTFE (polytetrafluoroethylene), alternative(?) to SS in safety valve, temperatures to 550F. (description see Small Parts Catalogue.)
 

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Justin
If and when you have some in stock, I'll purchase three for the AC-11!!
Excellent work and hope the progress continues to develop the safeties into more of true scale offering
 

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Also try Mc Master-Carr, they have some precision ground SS balls. If we had the safety on top of the steam dome, that would leave more space for a whistle, right Jason....:rolleyes:" border=0>
 
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