Fixing leaky steam valve

[HobbsParticipant @edwardhobbs3]

Hallo Folks,

I have a leaky injector steam valve on my Polly 1 that I need to fix, I was going to purchase a straight replacement but with Polly being halfway through transfer to a new owner they don't have any in stock and so I figured I'll try fix it myself.

I've highlighted the issue in the picture, but short version is there's a ding in the valve sealing surface and it's allowing steam to pass through.

The valve is made of a stainless steel cone which is screwed in and seals against the round hole.

I can make a fixture with the correct threads to get it mounted in the lathe, and my current plan is to remove material from the face very slowly until i get a clean circle all the way around – this means i don't have to worry about concentricity too much as I'm not making new holes.

My question:

Does this hole need to be chamfered to better fit the cone, or is a sharp edge the way to go for the best sealing surface? If a burr is raised on the inside of the hole, how would you go about removing it while keeping that edge? deburring tools seem to leave an uneven finish which i'm not sure would seal properly.

Thanks,
Ed

[HobbsParticipant @edwardhobbs3]

[BazParticipant @baz89810]

If you face from the centre outwards you should not get a burr, I would leave a sharp edge and let the stainless bed in to it.

[BazParticipant @baz89810]

Just bumping this up. Thought loads of you would have some advice on this.

[HobbsParticipant @edwardhobbs3]

Hi Baz,

Sorry for the delay, I'm terrible at remembering to check back on these posts – thank you for the advice, it seems obvious in retrospect but I completely missed it.

I re-faced the valve a week or so ago, using your tip and facing from the inside out and leaving the sharp edge to allow the cone to bed itself. I used a piece of acetal plastic i had and threaded it to hold the valve in place, then took very light cuts around .001" at a time until i couldn't see the dent.

I finally was able to test my repair yesterday and it seems to have worked well, no more steam coming out the injector! (unless I want it to ).

[Author]

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