Air Pump D Valves

[Builder01]

Another material to explore is 4301 Torlon. It is very expensive, but affordable scraps of it show up occasionally on Ebay. I have some and hope to make some experiments with it. Here is the product description:

Torlon 4301 Stronger and Tougher than PEEK and polyimide from cryogenic to 500°F

Torlon 4301 is a high modulus polyamide-imide containing graphite and PTFE for improved wear resistance. It is the general purpose wear grade of Torlon with an excellent balance of strength and impact resistance. It offers a wear rate that is 10% that of non-reinforced Torlon 4203 and has a CLTE that approaches that of many metals.

Torlon 4301 is ideal for:

Bushings(highly loaded)
High temperature wear pads
Thrust washers

Seems this material might be good for a slide valve.

[Bill Shields]

Be aware that this PEEK needs to be contained in a frame. You cannot push it back and forth with a spool like BvB designed...hence making a 3/4" scale pump is tough since all the necessary parts will not fit.

The recent design in LSORR is a masterpiece of ingenuity

[daves1459]

I was unaware of the Torlon 4301 and will look into it. Thanks for the tip. Same for the PEEK material. I'll look into that also. Being that it is carbon fiber impregnated I thought it not an issue. I've heard that those using virgin Teflon have to use a frame. As I recall the spec. sheet gave the PEEK stuff a strength of 12,000 psi at room temperature and 2,000 at 400F. I thought that enough too. The spec. sheet specifically states water and steam compatible.

Oh well I'll give it a try, Dave

[Bill Shields]

2000 psi, being shoved back and forth by a narrow shoulder will quickly end up with a dimple and lose valve travel.

by all means try it...but don't be surprised if you lose functionality..

[DMetzger]

My company uses Torlon for some high performance components. It is great stuff, and could be very good for steam and high heat. When made properly, I have seen some Torlon properties meet many metals, especially strength and wear.

But study the specs very carefully. Most of the time, Torlon needs to be heat treated after machining. Some part shapes have to be premachined, with about 0.010 stock remaining, then heat treated, then finished machined. It depends on the Torlon grade, the shape of the part, and how much material is removed. From my memory, the heat treat process is usually done in steps, with the highest temp around 500F. But check the spec sheets for your specific grade of Torlon.

We had a long series of problems, where our customer specified Torlon on some specific parts, with no heat treat. That grade was very sensitive to moisture, and the material properties would change dramatically with small changes in temperature and humidity. Lots of finger pointing where it works fine here, but a total disaster there. Once both companies figured out the heat treating and machining processes, all was well.

[Fender]

Would glass-filled PTFE have the same problems as the Torlon?

[Bill Shields]

you do not want to use glass filled anything as a slide valve surface....

[Builder01]

Yes, glass filled anything will work just like sandpaper! 4301 Torlon does not absorb moisture and may be worth experimenting with for slide valves. It is impregnated with Teflon and graphite. As Bill has mentioned, it is not clear if any material other than metal for a slide valve will keep sharp corners well enough from the abuse from the valve rod. If the valve material starts to deform in any way, your timing will be lost.

[daves1459]

2000 psi, being shoved back and forth by a narrow shoulder will quickly end up with a dimple and lose valve travel.

by all means try it...but don't be surprised if you lose functionality..

I get your point. Especially designs like I'm considering where over travel between the piston and valve call for free play between the valve rod and valve resulting in impact. Your doing a good job of talking me out of this PEEK stuff! I'll have to wait for the next issue of LSORR to find out how the designer handled the problems.

The Torlon is incredibly expensive. There is a point where cost exceeds value.

Dave

[Fender]

I found this item on ebay. PEEK 1.0 in. diameter, 3.0 in. long.

[Bill Shields]

i would suggest as an alternative:

Make the steam chest (where the post surface is) out of phosphor bronze.

Make the valves out of brass

note;

ever see a Raritan in native form? (or am i giving away my age???)

Brass on brass and nary a lubricator in site....

our steam is generally so wet that it is self lubricating

[Builder01]

Hi Bill, that is exactly what I did on my Van Brocklin pump, but the reverse. Brass port face, (cylinder block) with phosphor bronze slide valves. So far, so good!