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Pneumatic Bell Ringer

The solenoid bell ringer solution (previous page) wasn't loud enough and didn't want to revisit that solution.  A pneumatic bell ringer would be much nicer.  I looked at many bell ringer plans from others but found nothing that moved the clapper “inside” the bell.  Most of the existing plans were ones that swung the bell back and forth with the clapper hanging freely inside the bell.  Unfortunately, the only option available was to see if I could design and make one myself.  The first thing to consider was the size of the ringer.  It had to fit inside the bell I had which is 3" high with 3-3/4" mouth and an inside upper diameter of 1-3/4".

At first, I tried dozens of homemade designs with tiny sliding pistons, elaborate air passages, needle valves, etc.  All failed.  The picture below is what persistence is about.  Actually, the picture below shows only a small portion of the failed attempts as parts were reused to fit other designs.  Need I say a ton of time was spent making this scrap.

The large object at the top is a full size ringer. 



I was wondering how the heck did the full scale ones work?  The only way to find out was to get one and take it apart.  Well, it wasn't that easy.  The full scale ringers only have a few parts but still confused me to no end.  After more time, I began to figure it out at least enough to build a smaller scale one.  Still not sure 100% how it works.  What was different than all my previous designs was that it used an air chamber to regulate the timing.  Since the air chamber could not be scaled down (like the piston/cylinder/clapper) a larger area than planned would be needed.

Finally, after more tinkering, I settled on a design that worked great.  It only required a few parts but the machining/fitting was the key.  The overall size (1-1/2" diam) of the ringer just about filled the upper portion of the bell.






Here's what the ringer looks like all assembled.  The upper portion houses the piston/cylinder and air chamber.  The clapper's length and weight is purposely oversized.  That will be explained later.  The total length from the casing to the clapper is just over 4 inches.








Before getting started on building the ringer, here's an explanation (my best guess) of how it works.  It is similar to the full scale units which use an ingenious design.  Knowing how it works will help in getting it to run properly after the machining is done.



No matter what your application and size requirements, the operation is the same.


Now that you know how this thing works, lets start making chips...






Brass was used on all parts unless otherwise noted.  If you’re good at drilling small holes in stainless steel, use it for the piston.  I’m not, and used brass which worked fine.  There are only a few parts but machining is critical for proper operation.  Here's the finished ringer disassembled.  A parts list is at the end of this page.



This ringer is a finicky bugger.  I felt like a clock maker fiddling with it to get it to run properly.  Industry standard o-ring groove specs do not work with this ringer.  They are too tight fitting.  You may need to sand, file, etc. just to get the right fit.  The dimensions for this ringer will get you close, but after the machining is done, the work begins.  The geometry of the clapper's pivot point, arm angle/position, length and weight ALL have to be taken into consideration.  Unless your bell is exactly like mine, you will need to make changes.  To let you know what you're dealing with, I took apart a perfectly working ringer and re-assembled it.  It wouldn't run until I "broke it in" again for a few seconds.  If this was easy, I think there would be many variants of this ringer out there.  I haven't found any in this scale.

The full scale unit is CNC made.  If that option was available to me I think none of the fiddling around with clearances would have been necessary.  I did the best I could do with the equipment and talent level I have.










The casing is made from 1-1/2” diameter brass rod cut to length with the ends cleaned up.  A portion inside the casing is hollowed out for the air chamber which is needed for timing the activation.   The dimensions for the air chamber are not that critical as long as the total area stays about the same.  The air chamber limits how small this ringer can be made.

A 1/16” drill is used to make the air passages in the casing (both vertical and horizontal).  After drilling the horizontal air passage, plug the entrance hole by either soldering or tapping/plugging. 






The piston needs to hold tight tolerances.  Many small holes need to be drilled (#78, #65, #57, etc.).  I would have used SS for the piston but trying to drill tiny holes in SS is beyond my talent level so brass was used which worked fine.  The O-rings fit looser than normal as friction needs to be minimized.  The piston (without the o-rings) should move up/down in the cylinder using gravity only.




Casing Cover

The top casing cover uses a 5/16-18 stainless steel threaded rod to mount the bell/ringer when assembled.  The SS rod is drilled out using a 1/16” drill then threaded on to the brass cover using thread locker.  The top of the rod was tapped 10-32 to accommodate an air connection.   Ten 1-72 screws are used to attached the cover. 



The passages on the bottom of the top cover are to allow the air to flow into the air chamber when the piston moves upward against the cover.  You'll need to make a gasket also.







The clapper arm was cut from ¼” steel plate.  A brass weight was used to strike the bell and was threaded onto the clapper stem.  Since this is a scaled down version of the original, the clapper needed to be longer and heavier than wanted.  The weigh was needed to have gravity reset the ringer.  In previous versions, a spring was used with a smaller clapper.  The spring required very fine adjustments to get it to work.  The spring was nixed and decided on gravity which was more reliable.

The angle of the upper portion (which I'll call the "arm") is absolutely critical to the geometry of the ringer.  It is also important that the "arm" is above the pivot point for maximum leverage.  The clapper also needs to be at least 1/16" away from the bell after striking it so it doesn't muffle the ringing.  A 1/8" pin was used to secure it to the bracket.



Clapper Mounting Bracket

The mounting bracket is fairly simple.  The one in the picture is different as I was using it to try different hole locations. 



Here it is, all put together.



You only need to do these first few steps once all the clearances are obtained. 

All surfaces need to seal with minimal friction.  The piston (without the o-rings installed) should slide up down from its own weight.

- Install the large Dash 011 o-ring on the piston and install in the casing.  Make sure the fit can slide as free as possible without leaks.  This might take sanding, filing, honing, etc.  Take the large o-ring off.

- Install the smaller Dash 006 o-ring.  Re-install in the casing and do the same thing as in previous step.  Reduce all friction as much as possible. 

- Install both o-rings on the piston and re-install in casing (use a small amount of pneumatic lubricant).  Make sure the piston/o-rings move smoothly.

- Install the Dash 010 o-ring in the bottom of the casing and cover with the clapper bracket.  The clearance for this o-ring does not follow "standard" o-ring groove specs.  It is only 0.063" deep and the o-ring is 0.070" thick.  The clapper bracket squeezes the o-ring when installed.  I found that doing this reduces the chance of any air leaks and allows the air to exhaust more precisely.   Modify as necessary to allow the piston to slide easily.

- Once everything is moving freely, attach the casing cover and gasket to the casing using ten 1-72 screws.  It is important the INPUT air passages do not leak between the cover and the casing. 

Next step is testing...



THE RINGER WILL PROBABLY NOT WORK THE FIRST TIME!!!   I don't know how much clearer I can make this.  Here's what you will need to do to get it running. 

- Assemble the ringer per above (without the clapper).  Use pneumatic oil on the o-rings.

- Apply air supply (about 80psi for initial testing)

- The piston should pop through the bottom.  You should hear a burst of air exhaust through the 4 piston holes

    - If you hear/feel air continuing to leak, the issue is most likely a leaky bottom o-ring.  Fix it.

    - If the piston doesn't pop through he bottom, a couple things can be the issue.

            - Any (or all) of the 3 o-rings are leaking

            - The seal between the cover and the casing is leaking

            - The piston can't freely move

            - The 0.016" diam hole at the top of the piston is plugged

- With the piston fully extended, push the piston in about a 1/16".  The piston should then pop back inside the rest of the way.

    - If the piston doesn't retract with a slight nudge, similar issues may be the cause.

             - Any (or all) of the 3 o-rings are leaking

            - The piston can't freely move

Once the ringer casing/piston is operating properly, install the clapper onto the bracket using a 1/8” diameter pin.  The clapper design provided is "fine" tuned meaning the length, weight, angle and placement are all linked together for a properly running ringer.   Install the ringer assembly into the bell.  It will be secured using a 5/16-18 nut/washer when mounted.  Install an appropriate 10-32 air fitting onto the 5/16 stud.

The bell operates from 30-100 psi.  I use 50 psi since that is my brake supply pressure.  Running with a higher pressure will beat the crap out of the clapper/bell and will wear out sooner.  With the air pressure applied, the piston should push down pressing against the clapper arm.  There should be about a 1/16” space between the clapper and the bell when the piston is in the fully extended position.  This space allows the clapper to strike the bell and move back to avoid muffling the ringing.  You'll find that this space is critical to getting the ringer to reset also.  The weight, length and angle of the upper clapper arm all contribute to resetting the ringer.  All these will need to be customized to your application if size changes are made.  During testing, the bell/ringer assembly can be angled so the clapper is in a more horizontal angle.  This way gravity helps reset the ringer.  Once the ringer is broken in, it should work perfectly level and with lower (down to 30 psi) pressure.  Plan on spending some time doing this!


After running the ringer for a while, it may stop if you don’t lubricate it.  A squirt of good old pneumatic oil before running should last the day.



To activate the ringer I used a pneumatic switch from Clippard.





Here it is all done and working beautifully. 




Watch it in action here...


Was playing around with Fusion 360 and made this 3D animation of the bell ringer...




The ringer described above has been working every time I turn it on without any issues.  It even works better than the prior unit which used a spring to return the clapper.  We'll see how well it runs once it gets out in the elements for a few months and the temperature changes.

Well, after being outside for a year+ the ringer stopped working.  To see what was wrong, it was taken apart.  Two things were found...  The pneumatic oil used to lubricate the ringer got "sticky" and the clapper needed to be heavier to reset the piston.  After cleaning the ringer, WD-40 was used for lubrication instead of pneumatic oil.  A weight was also added to the clapper. These changed helped alot to get it to run more reliable.  We'll see after another year or so in the elements.



Here's a material list if interested.

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Last modified: 11/22/2021.