Safety valves

[nigelh]

Hi folks,
I have made the safety valves for my Simplex as per the drawings and, although they work (on compressed air) reasonably well, I cannot get them to seal completely at low pressure.
I have "dinked" a sacrificial 1/4" ball onto the cone seat but they are still leaking slightly (bubble test in water), even at 20psi.
My question is how can I get them to be 100% air/steam tight - is it necessary to lap the ball onto its seat and, if so, what lapping medium is best ?
Or am I expecting too much?  I'm sure I've seen locos in action without any whisp of steam from their safety valves!

Any hints/tips would be most welcome!
Thanks
Nigel

[jma1009]

hi nigel,

my proceedure is pretty much the same as for check valves. the safety valve is drilled through a tad undersize and the inside opened up then the seat is formed by a pin drill or boring tool BUT when at depth i stop the carriage and pull the lathe round by hand to avoid a partly formed seat leaving tool marks or any chatter. the hole through is then reamed. a bad seat wont be cured by 'biffing' a ball on the seat. for the 'biffing' i have a selection of hardened steel balls i use. if the safety valve is made in two parts and you can get at the seat easily then the finish on the seat can be inspected easily, and if ok can be burnished with a ball as per the late bill carter's method (see laurie lawrence's articles in ME on his standard injectors). never use the same stainless ball you may have used to biff the seat as the ball for the valve!

absolutely essential that the push rod that the acts on the ball via the spring doesnt have a tendency to tilt and that the ends of the springs are flat. i hand grind the ends of my springs then soften in the end of a lighter to red then press down on a piece of plate.

cheers,
julian

[nigelh]

Hi Julian,
many thanks for your help and advise.
I did "cheat" and make the valve in two parts so that the seat is removable - it was the best way I could think of to ensure that the seat was properly formed!
I have inspected it and it looks OK to me so a bit of burnishing may well help. Could you advise which issue of Model Engineer Bill Carters method is described in please? I don't have all issues of ME, sadly and google hasn't, yet, thrown up the relevant articles but I will continue to search meanwhile.
Thanks again,
regards
Nigel

[RGR 60130]

If making safety valves with removeable seats please look at the design very carefully to make sure the seat can't lift with the ball, thus closing off the escape path for steam.

This happened on a full size boiler and blew the arse out of it.

Please beware.

Reg

[nigelh]

Thanks Reg - very good point.
My seats screw in (5/16" x 32) from the bottom (inlet end) of the safety valve and have a larger dia (7/16") at the bottom so they cannot creep upwards to prevent just what you describe.
I guess, in theory, they could unscrew downwards (into the boiler) but that would result in dropping the blow off pressure, I guess.
Many thanks for the warning though - that would be a real disaster in the making!
Regards
Nigel

[jma1009]

for burnishing get a ball bearing of the same size as your safety valve ball, and using newspaper underneath the ball move the upturned seat on your valve around in a circular motion pressing gently.

tip - if you cannot suck through the bottom of the valve with the stainless ball in place by gravity then there some misallignment of the push rod and or spring when these are added. in theory with a round ball this shouldnt happen but it can! open out the hole in the top of the valve spring retainer/adjuster so the push rod is a sloppy fit. these days the push rod should be longer than the top of the valve with a slight recess cut into it so the push rod can be lifted with a pair of pliers. i think the SUPER SIMPLEX drawings show this.

it isnt unusual to get 'dud' batches of stainless balls from our suppliers which arent quite as circular as they should be. you may need to order some more.

cheers,
julian

[nigelh]

Thanks Julian - useful info and tips!
Regards
Nigel

[jma1009]

hope you have success after a few adjustments!

[jarin2]

hello friend safety valvas is most important thing of any machine this give support of any machine and nigelh thanks for this tips.
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TIPS FOR LOGO DESIGN

[Deleted]

Is this yet ANOTHER SPAMMER ?

[ronhancock]

Jul 15, 2013 8:57:20 GMT jma1009 said:

hi nigel,

my proceedure is pretty much the same as for check valves. the safety valve is drilled through a tad undersize and the inside opened up then the seat is formed by a pin drill or boring tool BUT when at depth i stop the carriage and pull the lathe round by hand to avoid a partly formed seat leaving tool marks or any chatter. the hole through is then reamed. a bad seat wont be cured by 'biffing' a ball on the seat. for the 'biffing' i have a selection of hardened steel balls i use. if the safety valve is made in two parts and you can get at the seat easily then the finish on the seat can be inspected easily, and if ok can be burnished with a ball as per the late bill carter's method (see laurie lawrence's articles in ME on his standard injectors). never use the same stainless ball you may have used to biff the seat as the ball for the valve!

absolutely essential that the push rod that the acts on the ball via the spring doesnt have a tendency to tilt and that the ends of the springs are flat. i hand grind the ends of my springs then soften in the end of a lighter to red then press down on a piece of plate.

cheers,
julian

Hi Julian you have so much amazing tips surprised how much is possible for us new bee's to learn big thank you
Ron

[pault]

Hi Nigel
You say "cone seat" does the ball sit in a countersink?

Regards
Paul