Lots of different check valves in saws / carbys. using the same principle, I made my own for a vintage 2 stroke engine from the 50’s for a non return valve for the fuel system. However I made this one fully serviceable from brass.
Check valves
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Tom , nice work. How long you have the lathe?
Could you draw a schematic of the parts/assy to better understand the workings?
Looks like the screen is held in with a piston pin clip, and the stem was soldered in place?
Could you draw a schematic of the parts/assy to better understand the workings?
Looks like the screen is held in with a piston pin clip, and the stem was soldered in place?
Hey mate, I’ve had the lathe about 6 months. For $500 USD it’s incredible. I had to do a number of tweaks and mods, but It holds within a micron over 10cm. I did a review on it here:
My drawing sucks, but this is the concept:
A pickup body which I put a step in to register the clip / filter-screen against. Inside that and about 2/3 up the pickup body I installed the valve seat. The was 0.02mm interference fit. The ball rests onto the seat. The pick up tube was machined with another interference fit of 0.02mm onto the seats outer diameter and pressed together. That assembly was soldered as a single, airtight unit.
I intended on being able to unthread it (hence the threads) but the parts so small and to thread them together tight enough while ensuring they stayed air tight was fiddly with smooth surfaces to hold and therefore that I decided to just solder them. When my knurling tool arrives in a few days I’ll be able to add texture and therefore friction which will help a lot for future projects that need to be threaded and unthreaded by hand.
That valve seat taper and width, distance to the outer wall and the horizontal platform between the two seemed to be really important. If the taper is too deep the ball doesn’t unseat easily and re-seats too tight requiring more vacuum to unseat again. If it’s not wide or deep enough the ballbearing rocks off too easily and won’t locate quickly and if the horizontal platform between the outer wall and taper is too wide, the ball can get easily dislodged into the corner and again reduces the speed it reseals.
In its current configuration I can have the valve nearly horizontal and it still seals in use while is easy to dislodge under vacuum and quickly reseals. It took me 3 tries to get the seat and ball to work well together.
Inside the pickup tube is a second screen a few millimeters up which retains the ball, allows is to unseat and the fuel to flow up the pickup body.
To clean it, you take the c-clip out and the first main screen comes out, then using a thin punch, you push up on the ball and that and the second screen travels up the pickup tube together and out the other end.
You can get long cotton swabs in the brass tubing and down to the seat for cleaning, the ball can be cleaned or replaced and the two screens can be cleaned or replaced too.
The circlip is a snug fit and makes a subtle satisfying click when installed, but I purposely didn’t create a notch for its circumference to locate in which would make this style impossible to remove without damage and easy enough to install with a pick and firm pressure.
My drawing sucks, but this is the concept:
A pickup body which I put a step in to register the clip / filter-screen against. Inside that and about 2/3 up the pickup body I installed the valve seat. The was 0.02mm interference fit. The ball rests onto the seat. The pick up tube was machined with another interference fit of 0.02mm onto the seats outer diameter and pressed together. That assembly was soldered as a single, airtight unit.
I intended on being able to unthread it (hence the threads) but the parts so small and to thread them together tight enough while ensuring they stayed air tight was fiddly with smooth surfaces to hold and therefore that I decided to just solder them. When my knurling tool arrives in a few days I’ll be able to add texture and therefore friction which will help a lot for future projects that need to be threaded and unthreaded by hand.
That valve seat taper and width, distance to the outer wall and the horizontal platform between the two seemed to be really important. If the taper is too deep the ball doesn’t unseat easily and re-seats too tight requiring more vacuum to unseat again. If it’s not wide or deep enough the ballbearing rocks off too easily and won’t locate quickly and if the horizontal platform between the outer wall and taper is too wide, the ball can get easily dislodged into the corner and again reduces the speed it reseals.
In its current configuration I can have the valve nearly horizontal and it still seals in use while is easy to dislodge under vacuum and quickly reseals. It took me 3 tries to get the seat and ball to work well together.
Inside the pickup tube is a second screen a few millimeters up which retains the ball, allows is to unseat and the fuel to flow up the pickup body.
To clean it, you take the c-clip out and the first main screen comes out, then using a thin punch, you push up on the ball and that and the second screen travels up the pickup tube together and out the other end.
You can get long cotton swabs in the brass tubing and down to the seat for cleaning, the ball can be cleaned or replaced and the two screens can be cleaned or replaced too.
The circlip is a snug fit and makes a subtle satisfying click when installed, but I purposely didn’t create a notch for its circumference to locate in which would make this style impossible to remove without damage and easy enough to install with a pick and firm pressure.
This gives you a look of the valve in use with fuel in the tube. This was just testing it before I pressed the valve into the pickup body. Note the slight lip at the bottom. Unnecessary as I used solder, but it was a thin skirt that was intended to increase the seal between the valve and pickup body. 
Thanks Tom.
Sounds like it took some experimentation and tinkering to get the engineering right, but the final design turned out well.
Curious what sort of engine this is for? I fix up old stuff too!
Thanks mate, yes lots of tweaking, especially as the designed changed a number of times throughout the project haha. It’s interesting how a design can work in your head, but in practise you come across reasons why it’s not so plain sailing lol.
The ball and the socket is one of the simplest check valves and utter simplicity. I see the frustration in getting the socket sized properly. The design is nice as it's also easily serviceable.
One of the reasons I like old machines is you can fix them with simple tools; I hate the new cars and trucks horror show to work on.
I’m beginning to understand how even the simplest of parts have a lot of r&d behind them though lol.
Sometimes I will try and fix / simplify something to quickly find out that there is often a lot more of thought and care gone into the design than I realised.
I agree, I love things that can be disassembled, repaired and rebuilt. With that said though, also a design that is conducive to doing so is where the elegance really is. That’s why I enjoy making things from scratch, I can make them how I want lol.
Of course all the things I make are simple and anyone can do it, real engineering and skill that Allen Millard has is what inspires me! Check his YouTube channel out
Sometimes I will try and fix / simplify something to quickly find out that there is often a lot more of thought and care gone into the design than I realised.
I agree, I love things that can be disassembled, repaired and rebuilt. With that said though, also a design that is conducive to doing so is where the elegance really is. That’s why I enjoy making things from scratch, I can make them how I want lol.
Of course all the things I make are simple and anyone can do it, real engineering and skill that Allen Millard has is what inspires me! Check his YouTube channel out
I'm basically a parts replacer. But, this is a really interesting thread.
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