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Water Gauge tapered cock details

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Brian Abbott19/03/2021 22:35:17
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491 forum posts
93 photos

I am looking at making a new set of water gauges.

Would anyone know of an article to point me in the right direction to make the tapered cocks accurately so they seal?

Also, I notice many are advertised as having PTFE deals, does anyone have a design?

Thanks

Paul Kemp19/03/2021 23:27:45
710 forum posts
27 photos

I made my own and shortly to make another for my half size engine. Tapered plugs in bronze bodies I have never had much luck with, full size tend to have sleeve packings but they can still be tight to operate. I have made mine (2 sets for the Ruston SD 4" plus the drain cocks) with parallel stainless plugs running in a PTFE sleeve. No particular mystery to them I just make the OD of the sleeve 2 - 3 thou bigger than the bore in the body, the latest set of drain cocks have a nominal plug size of 1/4" and an OD of 11/32. I make a press dolly the OD of which is 5 thou under 1/4" to support and guide the PTFE sleeve and press in with the bench vice. Once pressed in obviously the bore of the sleeve reduces and I turn the plug to be a neat push fit. As PTFE has a high expansion rate if you make them too tight they are hard to turn when hot! The Ruston has 2 gauges and they have been in service for 9 years now and have so far never needed any attention and they close off dead tight with no leakage. If you are on TT you can see pictures there.

Paul.

Brian Abbott20/03/2021 13:03:35
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491 forum posts
93 photos

Hello Paul,

Thanks for the reply, do you have a user name on Traction Talk i can use to find you?

Paul Kemp20/03/2021 15:54:00
710 forum posts
27 photos

Hi,

Paul30013. There is some stuff on there from around 2012 for the ones I did for the Ruston and only a week ago for the 6" LS drain cocks.

Paul.

fizzy20/03/2021 16:21:04
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1840 forum posts
120 photos

I tried for years to get mine to seal using a 10 degree taper, then one day changed the taper to 2 or 3 degrees and never had one leak since. It takes a bit of practise but they work great now. Mine are brass in brass.

Brian Abbott20/03/2021 21:51:23
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491 forum posts
93 photos

Thanks both for the replies, and thanks Paul, I will have a look.

Martin Kyte20/03/2021 22:38:07
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2721 forum posts
48 photos

Turn the taper on the plugs and then at the same setting turn a piece of silver steel to make a tapered reamer to cut the seatings.

That way the plugs and the seating have to be the same and you always have a reamer to reseat a worn valve.

regards Martin

Paul Kemp20/03/2021 23:04:29
710 forum posts
27 photos

Generally slow tapers (sub around 10 degrees) are considered locking tapers (Morse etc) so I am slightly surprised fizzy's at 2 - 3 degrees do not grab. I played around with taper plugs (yes I made reamers too) and yes I have one on the pump bypass of the 6" engine which is yet to be proven in service over time. In that application a small degree of leakage even when closed - internally is not a major issue but even having turned the plug and reamer at the same setting I had to lap it afterwards and fit an o ring at the gland nut to prevent external leakage under pressure. Comversely all the parallel plug valves with PTFE sleeves I have made so far (over a dozen) have been leak tight right from the off with no fiddling around. They are so easy to make I won't be changing any time soon. Also easy to repair in the future, just knock the sleeve out if ever needed, machine a new one and press in. I made the pair of sleeves for the 6" drain cocks in less than 10 minutes.

Paul.

Brian Abbott20/03/2021 23:34:59
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491 forum posts
93 photos

Hello Paul.

How do you get on with turning the PTFE?, just very sharp tooling i guess ?

Paul Kemp21/03/2021 01:09:00
710 forum posts
27 photos

Brian,

For the bores I started out reaming but when I realised the compression changes the bore on installation anyway I just drill it. Run at about 800rpm for say the 1/4" hole. I usually put a pilot in first I think I used 3/32 for the latest ones (not critical). Turn the outside with a HSS knife style tool around 4 degrees front and side clearance, minimal top rake (sideways if you get my drift), never fussed about the actual angles just grind to what looks right! Swarf comes off in coiled ribbons, just keep it away from the job as it will tangle if you give it chance. Surface finish is a dull polish but it's not that important as it tends to shave when you press it in anyway. I find it really easy to machine but watch the fumes. One tip, if you pressure test straight after assembly (air in water) you will get a few bubbles. If you boil it in water for 5 mins or so it will be tight. On the Ruston when doing a cold hydraulic you get a couple of drips of water but in steam it's as tight as a drum. I broke a glass on the Ruston with the shovel! It shut off completely and I carried on using the other glass to get back to base! Drill the passage for the steam / water after you have pressed it in.

Paul.

D.A.Godley22/03/2021 16:20:23
120 forum posts
39 photos

Would a look at Engineering In Miniature ( Mods please excuse) Dec 2005 page 176 help you at all ? .

Brian Abbott22/03/2021 16:29:58
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491 forum posts
93 photos

Hello D.A.Godley.

I think Paul has set me off in the right direction so hopefully i should be ok.

Unfortunately i don't take Engineering in Miniature, if there an article ?

D.A.Godley22/03/2021 17:21:14
120 forum posts
39 photos
Posted by Brian Abbott on 22/03/2021 16:29:58:

Hello D.A.Godley.

I think Paul has set me off in the right direction so hopefully i should be ok.

Unfortunately i don't take Engineering in Miniature, if there an article ?

There is an article by Doug Hewson , I have tried to upload photos to a folder but failed . If you pm me an email address, I will forward it to you .

regards

David

Brian Abbott22/03/2021 22:39:45
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491 forum posts
93 photos

Thanks David,

Pm sent.

Brian Abbott05/04/2021 18:40:44
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491 forum posts
93 photos

Hello Paul.

Dropped you a PM if you get chance.

Thanks

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