# Making a pop valve?



## Jack - Freshwater Models (Feb 17, 2008)

I am starting to build a loco. Years ago I was able to easily buy safety valves from Fyne Fort Fittings but now I can't find anyone with a safety valve to suit my needs. I made a safety valve yesterday and sadly I couldn't get the .156dia ball to seat in the .125" hole well enough to hold air at the desired pressure. Always a minor leak.

Any advice on making safety valves?

Jack


----------



## DKRickman (Mar 25, 2008)

Get another ball, mount it rigidly on a rod, and use that to lap the seat. 

Place a spare ball in the hole and hit it with a hammer to form the seat. 

Use a high temperature plastic ball, which will deform slightly to the seat.


----------



## Two Blocked (Feb 22, 2008)

In my experience the key ingrediant is to pre-drill the steam passage from the direction of the steam flow and then to ream the hole to size from the same direction. Most steam relief/safety valves are drilled from the other direction. What is over looked in this intuitive approach is that a two lipped twist drill tends to describe cyclodial arcs upon entering the parent material. This will result in a tri-cornered hole at the surface which will never provide a uniform sealing ring at its tangent with the spring loaded ball. Think about the last time you used a two lipped twist drill to drill a hole in thin sheet metal. Do you remember that funny triangular hole that you produced? If a hole is deep enough the drill will slowly become a gun drill of sorts and the deeper part of the hole will become darn round in shape, but the entry point retains the tri-corner shape. 
This is the point where most folks resort to the-beat-it-with-a-ball-bearing approach to attempt to "round out" the seat; it has never worked for me. It's best to do it right the first time around. Drill and ream in the direction of the steam flow whether you C-bore first or last; I perfer first.


----------



## Alan Wright (Jan 9, 2008)

There have been several very good articles that would lead you through the process. There have been several in the G1MRA NL & J that many of us refer to when making these items. Saves allot of frustating trial and error.


----------



## Jack - Freshwater Models (Feb 17, 2008)

Posted By Two Blocked on 08 Mar 2010 06:49 AM 
In my experience the key ingrediant is to pre-drill the steam passage from the direction of the steam flow and then to ream the hole to size from the same direction. Most steam relief/safety valves are drilled from the other direction. What is over looked in this intuitive approach is that a two lipped twist drill tends to describe cyclodial arcs upon entering the parent material. This will result in a tri-cornered hole at the surface which will never provide a uniform sealing ring at its tangent with the spring loaded ball. Think about the last time you used a two lipped twist drill to drill a hole in thin sheet metal. Do you remember that funny triangular hole that you produced? If a hole is deep enough the drill will slowly become a gun drill of sorts and the deeper part of the hole will become darn round in shape, but the entry point retains the tri-corner shape. 
This is the point where most folks resort to the-beat-it-with-a-ball-bearing approach to attempt to "round out" the seat; it has never worked for me. It's best to do it right the first time around. Drill and ream in the direction of the steam flow whether you C-bore first or last; I perfer first. 


Two Blocked,

Thanks for your reply. Useful reply! I will approach from the bottom of my valve in the next try. 

Do you think diameter in the seat in relationship to the ball diameter makes a difference. I realize that the size of the hole determines the amount of force to hold the ball down due to the area of pressure. I am mainly concerned with seating.

Jack


----------



## David BaileyK27 (Jan 2, 2008)

I agree about the Reaming, but if you are trying to make a pop valve then you need a double seat to get the pop action, the size of the second seat needs to be larger than the ball and the depth is a matter of trial and error, the gap left between the second seat and the ball is the criticle factor also the ball holder and the inside diameter of the valve body is also another factor which will alter the pop action. 
So its not as easy as it seems, I have been making pop valves for a long time and although we have our parts CNC machined they sill need "tuning" to get a decent pop action. 
David Bailey www.djbengineering.co.uk


----------



## Kovacjr (Jan 2, 2008)

Take a look at the article by Kozo in Live Steam on safetys. Very helpful.


----------



## Jack - Freshwater Models (Feb 17, 2008)

Jason, 

If I had the article I would! 

Jack


----------



## steamboatmodel (Jan 2, 2008)

It is in his Building the New Shay Book. He also has articles on Safety of Copper Boilers, the one on Safety Valves, Tube Joints, O-rings for Live Steam Service and Small Hexagonal Head Screws. Even If Shays are not you thing it is a book worth picking up for the ideas, charts and methods in it. 
Regards, 
Gerald.


----------



## Jack - Freshwater Models (Feb 17, 2008)

Gerald, 

Thanks for the reference to the book! Probably easier than finding the magazine. 

Jack


----------



## Jack - Freshwater Models (Feb 17, 2008)

Posted By Two Blocked on 08 Mar 2010 06:49 AM 
In my experience the key ingrediant is to pre-drill the steam passage from the direction of the steam flow and then to ream the hole to size from the same direction. Most steam relief/safety valves are drilled from the other direction. What is over looked in this intuitive approach is that a two lipped twist drill tends to describe cyclodial arcs upon entering the parent material. This will result in a tri-cornered hole at the surface which will never provide a uniform sealing ring at its tangent with the spring loaded ball. Think about the last time you used a two lipped twist drill to drill a hole in thin sheet metal. Do you remember that funny triangular hole that you produced? If a hole is deep enough the drill will slowly become a gun drill of sorts and the deeper part of the hole will become darn round in shape, but the entry point retains the tri-corner shape. 
This is the point where most folks resort to the-beat-it-with-a-ball-bearing approach to attempt to "round out" the seat; it has never worked for me. It's best to do it right the first time around. Drill and ream in the direction of the steam flow whether you C-bore first or last; I perfer first. 


Of all the posts this was the most useful. I just finished popvalve MK2 and it sort of works. The seat seems to seal though when the valve pops it seems to need a nudge to reseat. 

Time to try again! This time I will be drilling against the steam and reaming with the steam. 

Jack


----------



## Steve Shyvers (Jan 2, 2008)

Jack, 

Regarding valve seat diameter to ball diameter several sources that I've come across indicate that it should be about 80% for a pop valve. In a pop valve the ball sits down in a counterbore, and the botom of the counterbore should be flat or slightly convex so that the ball seats against a sharp edge. A concave bottom such as a regular twist drill makes isn't what you want. After drilling the counterbore part way with a regular twist drill use a "d-bit" to cut the counterbore to depth. I've made d-bits for cutting brass from the shanks of stainless steel bolts. The stainless is hard enough for limited use with brass if you use plenty of lubrication with it, and the stainless avoids having to harden the bit. Fabrication is simple turning to diameter, hand filing to profile the "d" portion, and final touch up of the edges on a sharpening stone. 

As David Bailey said, the counterbore diameter and depth are critical, to which I'll add the spring tension and the back pressure above the ball when the ball lifts. I think Kozo covers the recommendations for sizing the counterbore diameter ( I cannot remember right now) and he discusses tuning the back pressure. With the counterbore diameter fixed you are left with counterbore depth, spring tension, and back pressure to play with. I modified a commercial safety valve to a pop valve, and to do the final tuning I was making milli-inch adjustments to the counterbore depth, with steam tests between each cut on the lathe. Fun! My goal was to get the safety to lift at 60 psig and then to close after dropping the boiler pressure by about 10%. It works but there are still times when it will pop twice rapidly in succession or refuse to seat properly. Sounds pretty interesting though. Sort of a "strawberry" sound instead of a sharp "pop". 

Steve


----------



## xo18thfa (Jan 2, 2008)

Here's an idea I want to try. It eliminates the ball valve and uses an O ring instead. It says to use bronze for the valve body, but brass works fine











I took another look at Kozo's article. There is some real brain surgery machine work to do in the garden RR size. You almost need a rotary table and mill with a tilting head to do the adjusting plug.

Bob


----------



## Jack - Freshwater Models (Feb 17, 2008)

Posted By Steve Shyvers on 09 Mar 2010 09:49 AM 
Jack, 

Regarding valve seat diameter to ball diameter several sources that I've come across indicate that it should be about 80% for a pop valve. In a pop valve the ball sits down in a counterbore, and the botom of the counterbore should be flat or slightly convex so that the ball seats against a sharp edge. A concave bottom such as a regular twist drill makes isn't what you want. After drilling the counterbore part way with a regular twist drill use a "d-bit" to cut the counterbore to depth. I've made d-bits for cutting brass from the shanks of stainless steel bolts. The stainless is hard enough for limited use with brass if you use plenty of lubrication with it, and the stainless avoids having to harden the bit. Fabrication is simple turning to diameter, hand filing to profile the "d" portion, and final touch up of the edges on a sharpening stone. 

As David Bailey said, the counterbore diameter and depth are critical, to which I'll add the spring tension and the back pressure above the ball when the ball lifts. I think Kozo covers the recommendations for sizing the counterbore diameter ( I cannot remember right now) and he discusses tuning the back pressure. With the counterbore diameter fixed you are left with counterbore depth, spring tension, and back pressure to play with. I modified a commercial safety valve to a pop valve, and to do the final tuning I was making milli-inch adjustments to the counterbore depth, with steam tests between each cut on the lathe. Fun! My goal was to get the safety to lift at 60 psig and then to close after dropping the boiler pressure by about 10%. It works but there are still times when it will pop twice rapidly in succession or refuse to seat properly. Sounds pretty interesting though. Sort of a "strawberry" sound instead of a sharp "pop". 

Steve 

The one I built this am is very close to working. The ball seats but needs just a touch of pressure on the stem to get it to shut. I will try another with a shorter lift. On air this valve makes a rasberry sound when it opens.

I made a square end bit that does nicely for cutting the square bottom holes. First I drill the hole with a regular bit. Then I drill with a squared off bit. The squared off bit is just a regular bit sharpened to a square shape rather than a pointed shape. I have a poor mans DRO on my lathe tailstock so I can easily measure the depth of cut.

Jack


----------



## Jack - Freshwater Models (Feb 17, 2008)

Posted By xo18thfa on 09 Mar 2010 11:10 AM 
Here's an idea I want to try. It eliminates the ball valve and uses an O ring instead. It says to use bronze for the valve body, but brass works fine




I took another look at Kozo's article. There is some real brain surgery machine work to do in the garden RR size. You almost need a rotary table and mill with a tilting head to do the adjusting plug.

Bob 



Thanks for that drawing!

Jack


----------



## Steve Shyvers (Jan 2, 2008)

I meant "raspberry" instead of "strawberry" in my earlier post. Sorry. Too many distractions here in the spaceship while trying to communicate intelligently with earth. 

Steve


----------



## Semper Vaporo (Jan 2, 2008)

Posted By Steve Shyvers on 09 Mar 2010 01:29 PM 
I meant "raspberry" instead of "strawberry" in my earlier post. Sorry. Too many distractions here in the spaceship while trying to communicate intelligently with earth. 

Steve 



Well, there's yer problem... 'communicate intelligently with earth" indeed! Haa haa haa! You know what Kirk said when he landed here... "Beam me up, Scotty, there is no intelligent life here."


----------



## Dan Rowe (Mar 8, 2009)

Very interesting thread.

The point has been made but to clarify it a bit there are two types of valves used as a pop valve. 

In techinical terms one is a relief valve and the other is a safety valve. A relief valve is a simple spring loaded valve that will relieve and set at a pressure set by the spring. A safety valve is a bit more complicated. The force of the steam escaping is used to help hold the valve open after it has opened. This makes the valve close below the lift pressure.

Kozo describes a true safety valve with blow down. Full size valves and larger model valves have a adjusting ring for the blow down. Kozo's design has a machined ring that has to be adjusted as described. 

The other thing Kozo adresses is the relieving capacity of the valve. This is one of the only sources of this infromation I have seen. The capacity of the valve should be able to relieve the boiler when the throttle is closed and at full firing rate. It is nice to use engineering for this calculation insterad of guess work.

The drawing Bob posted is a relief valve with no provision for blow down but it is a simple design.
Dan


----------



## Jack - Freshwater Models (Feb 17, 2008)

It is nice to use engineering for this calculation insterad of guess work.



I prefer an "educated guess" insterad of "guess work" or "engineering" (since I'm not a real engineer) for this sort of thing. So many successful models have been built and their safety valves seem to work fine. For general size we can look to the work of LBSC, Poulter/Hines, Applegate, Martin Evans, etc.  or the various manufacturers like Aster, Accucraft, etc.

Jack


----------



## Jack - Freshwater Models (Feb 17, 2008)

Now about 1/4-40 ME threads. One problem I am having is making nice fitting ME threads. I can't get the adjusting screw to fit the threads in the valve body nicely. I am using a British made tap and a British made die. The die is the split type and I have forced it open as much as I can and it still cuts threads that are too small to fit the taped threads snugly. I am thinking it may be just a lousy tap/die and I need to replace them. 

Any ideas? 

Jack


----------



## rkapuaala (Jan 3, 2008)

What a great discussion. I feel like I'm right in there building a pop valve!


----------



## Steve Shyvers (Jan 2, 2008)

Jack, 

I've had the same experience. Things to try: teflon tape around threads, cut male threads to a slightly larger diameter on a lathe, pipe dope on threads (mostly softens and is removed by steam but enough might remain to keep adjusting screw from rotating), try a dab of paint on the adjusting nut after tuning the safety, lock ring around adjusting nut. 

Steve


----------



## Dan Rowe (Mar 8, 2009)

Posted By Jack - Freshwater Models on 09 Mar 2010 03:22 PM I prefer an "educated guess" insterad of "guess work" or "engineering" (since I'm not a real engineer) for this sort of thing. So many successful models have been built and their safety valves seem to work fine. For general size we can look to the work of LBSC, Poulter/Hines, Applegate, Martin Evans, etc. or the various manufacturers like Aster, Accucraft, etc.

Jack














Jack, Kozo used the safety valve designed by William Morewood for all his engines I do not have the Raritan book so I can not say if the tables Kozo presents are from there or not. He did modify the design in the New Shay book to add a replacable orifice. This makes it possible to adjust the blow down under pressure by changing the orifice. This makes dialing in the blow down pressure a much simpler operation than remachining the valve.

It is not required to be an engineer to read Kozo or any of the other engineers you mentioned.








Dan


----------



## xo18thfa (Jan 2, 2008)

Posted By Dan Rowe on 09 Mar 2010 02:41 PM 
Very interesting thread.

The point has been made but to clarify it a bit there are two types of valves used as a pop valve. 

In techinical terms one is a relief valve and the other is a safety valve. A relief valve is a simple spring loaded valve that will relieve and set at a pressure set by the spring. A safety valve is a bit more complicated. The force of the steam escaping is used to help hold the valve open after it has opened. This makes the valve close below the lift pressure.

Kozo describes a true safety valve with blow down. Full size valves and larger model valves have a adjusting ring for the blow down. Kozo's design has a machined ring that has to be adjusted as described. 

The other thing Kozo adresses is the relieving capacity of the valve. This is one of the only sources of this infromation I have seen. The capacity of the valve should be able to relieve the boiler when the throttle is closed and at full firing rate. It is nice to use engineering for this calculation insterad of guess work.

The drawing Bob posted is a relief valve with no provision for blow down but it is a simple design.
Dan

I wonder at what point the calculations Kozo does start to break down. Some things just don't scale.


----------



## xo18thfa (Jan 2, 2008)

Posted By Jack - Freshwater Models on 09 Mar 2010 03:27 PM 
Now about 1/4-40 ME threads. One problem I am having is making nice fitting ME threads. I can't get the adjusting screw to fit the threads in the valve body nicely. I am using a British made tap and a British made die. The die is the split type and I have forced it open as much as I can and it still cuts threads that are too small to fit the taped threads snugly. I am thinking it may be just a lousy tap/die and I need to replace them. 

Any ideas? 

Jack 
I do not to put the "potty mouth" on our U.K. friends, but I have trouble with U.K. made dies in 40 TPI. The taps work fine. 40 TPI is not unusual. It is a special instrument thread available from a number of tool companies. MSC Industrial Supply, Victor Machinery Exchange, and Traver's Tool have all the "M.E." sizes. Victor, for example carries 1/4" in 17 different pitches from 16 TPI to 80 TPI.

I am going to trade up to Victor or Traver's


----------



## xo18thfa (Jan 2, 2008)

Posted By Steve Shyvers on 09 Mar 2010 01:29 PM 
I meant "raspberry" instead of "strawberry" in my earlier post. Sorry. Too many distractions here in the spaceship while trying to communicate intelligently with earth. 

Steve 


Steve: You are getting cranberry juice in the works again.


----------



## Dan Rowe (Mar 8, 2009)

Posted By xo18thfa on 09 Mar 2010 07:10 PM 
I wonder at what point the calculations Kozo does start to break down. Some things just don't scale. Good question Bob, I do not have a good answer. The safety valve designs in the New Shay book use 1/8", 5/32" 3/16", 1/4", 5/16" 3/8" & 7/16" balls. The smallest one with the 1/8" ball is smaller than the one in the drawing you posted. The one with the 5/32" ball is nearly the same size as your posted drawing. There will be as Kozo states a lot of variance in performance due to machining even if you go by his design exactly so the graph is only a starting point.

The only other place I have seen any extensive information about sizing a safety valve is the Australian Boiler code. It is covered in both AMBSC Part 1 Copper boilers and AMBSC Part 2 Steel boilers.
Dan


----------



## Jack - Freshwater Models (Feb 17, 2008)

Posted By xo18thfa on 09 Mar 2010 07:22 PM 
I have trouble with U.K. made dies in 40 TPI. The taps work fine. 





Bob,

Thanks for your input. I was beginning to think I was doing something wrong. The taps I have are kind of tired but not all that bad. The die I have is in a word crude so I placed an order with MSC which I have always had good luck with.

Regards,

Jack


----------



## Jack - Freshwater Models (Feb 17, 2008)

Regarding cutting threads for safety valves- 

I just opened the 1/4-40 taps/dies from MSC and tried them. I was amazed in the varience of thread size. The standard 4 flute taps are only available in H2 limits (I would have preferred H1) and are usually .2535 diameter. These make for a loose fit. 

However, I also bought a 2 flute gun tap with unknown H limits and it is .2515 dia and makes for a very nice fit. I will grind back the business end so as to get deeper into a blind hole. 

Jack


----------

